AMERICAN JOURNAL OF HUMAN BIOLOGY 20:510–529 (2008) Original Research Article Climate Variables as Predictors of Basal Metabolic Rate: New Equations ANDREW W. FROEHLE Department of Anthropology, University of California, San Diego, California 92093-0532 ABSTRACT Estimation of basal metabolic rate (BMR) and daily energy expenditure (DEE) in living humans and in fossil hominins can be used to understand the way populations adapt to different environmental and nutritional circumstances. One variable that should be considered in such estimates is climate, which may influence between-population variation in BMR. Overall, populations living in warmer climates tend to have lower BMR than those living in colder climates, even after controlling for body size and composition. Current methods of estimating BMR ignore climate, or deal with its effects in an insufficient manner. This may affect studies that use the factorial method to estimate DEE from BMR, when BMR is not measured but predicted using an equation. The present meta-analysis of published BMR uses stepwise regression to investigate whether the inclusion of climate variables can produce a generally applicable model for human BMR. Regression results show that mean annual temperature and high heat index temperature have a significant effect on BMR, along with body size, age and sex. Based on the regression analysis, equations predicting BMR from body size and climate variables were derived and compared with existing equations. The new equations are generally more accurate and more consistent across climates than the older ones. Estimates of DEE in living and fossil humans using the new equations are compared with estimates using previously published equations, illustrating the utility of including climate variables in estimates of BMR. The new equations derived here may prove useful for future studies of human energy expenditure. Am. J. Hum. Biol. 20:510–529, 2008. ' 2008 Wiley-Liss, Inc. The use of reference equations to estimate basal metabolic rate (BMR), the energy required for body maintenance and growth in the absence of digestion and physical activity, is common practice in human biology and biological anthropology when measurement is not feasible (Ulijaszek, 1995). Subsequent use of these BMR values to estimate daily energy expenditure (DEE) using the factorial method also occurs frequently. Factorial method studies of DEE are useful to understanding energy balance in living human populations, and adaptations to different environmental and nutritional circumstances (e.g. Gamboa and Garcia, 2007; Leonard et al., 1997, 2005; McNeill et al., 1988; Panter-Brick, 1993), informing agricultural and nutritional policy-making by government agencies (FAO, 1950, 1957; FAO/WHO, 1973; FAO/WHO/UNU, 1985), and investigating the energetic correlates of events in hominin evolution (Churchill, 2006; Froehle, 2007; Leonard and Robertson, 1994; Sorensen and Leonard, 2001; SteudelNumbers, 2006). This approach requires careful consideration of the sample from which any particular equation was derived, with regard to a number of variables that influence variation in BMR within humans. One must ensure that the equation to be used either controls for these variables, or was derived from a sample that, in terms of these variables, closely resembles the group to which the equation will be applied (Ulijaszek, 1995). Available equations often control for many of the relevant variables, but as will be seen below, none controls for all of them in a systematic and generally applicable manner. Incomplete consideration of these variables in an equation’s sample and also in the population under study can lead to inaccuracies in BMR estimates, which can further produce considerable error in DEE estimates using the factorial method. The factorial method, in its simplest form, uses the following equation: C 2008 V Wiley-Liss, Inc. DEEðkcal=dÞ ¼ BMRðkcal=dÞ 3 PAL where PAL stands for physical activity level and represents a coefficient that accounts for energy expenditure above basal conditions. Note that PAL can have a substantial influence on the error of DEE estimates, and that even when using measured BMR, the use of PAL can provide inaccurate DEE, especially in highly active populations (Leonard et al., 1997; Spurr et al., 1996a). The use of focal follows and scan sampling as opposed to subject activity recall diaries can improve PAL, and thus DEE, estimates, but this is not always the case (Durnin, 1990; Leonard et al., 1997; Spurr et al., 1996a). Although PAL plays an important role in the accuracy of DEE estimates, the present study focuses on the effect BMR values have on DEE accuracy with the factorial method. The use of measured instead of estimated BMR, for instance, can improve DEE accuracy by up to 19% (Leonard et al., 1997; Alfonzo-Gonzalez et al., 2004). Obviously this calls for the use of measured values, but field conditions can often make measurement impractical or impossible, requiring the use of predictive equations (Ulijaszek, 1995). As the above finding indicates, currently used equations to estimate BMR are not particularly good, at least for some populations. In the absence of measured BMR, then, the use of improved equations could increase Correspondence to: Andrew W. Froehle, Department of Anthropology, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 920930532, USA. E-mail: [email protected] Received 4 June 2007; Revision received 9 January 2008; Accepted 13 January 2008 DOI 10.1002/ajhb.20769 Published online 6 May 2008 in Wiley InterScience (www.interscience. wiley.com). CLIMATE AND BMR IN HUMANS the accuracy of subsequent DEE estimates. The magnitude of such improvements may be small, on the order of 200 kcal/d, and thus seemingly unimportant (Durnin, 1990). Nevertheless, as an example of the potential uses of this small quantity of energy, some have found the daily energy requirements of gestation to be 170 kcal/d (Thongprasert et al., 1987), and on average 200 kcal could meet the daily growth needs of 1.4 children between birth to 4 years old (Butte, 1996). Furthermore, small imbalances in energy intake over expenditure can over time affect overweight and obesity (Levine, 2003), two major health issues in population-level nutritional studies. Thus, errors in DEE estimates on the order of 200 kcal/d can represent the equivalent of bringing a child to term and subsequently providing for its normal growth, or the difference between normal, healthy weight and the health problems that accompany excessive weight. Concerns of this nature are quite relevant to applications of the factorial method in human biology and biological anthropology. In attempting to minimize inaccuracy in BMR and DEE estimates by choosing a population-appropriate predictive equation, one must consider several relevant variables. Body mass and body composition have been shown together to exert the largest influence on BMR, both on an interspecific scale and within humans (Cunningham, 1980, 1991; Kleiber, 1961; Nelson et al., 1992; Ravussin et al., 1986; Webb, 1981; Weinsier et al., 1992). These variables are almost universally controlled for in predictive equations by using body mass or fat-free mass (FFM) as the independent variable from which BMR is estimated. Some evidence suggests that BMR in humans also varies with sex and age, though considerable debate surrounds the precise nature of these relationships (Buchholz et al., 2001; Calloway and Zanni, 1980; Ferraro et al., 1992; Froehle and Schoeninger, 2006; Henry, 2000; Holliday, 1986; Keys et al., 1973; Klausen et al., 1997; Nichols et al., 1990; Piers et al., 1998; Sathyaprabha, 2000; Vaughan et al., 1991). To control for these variables, many past BMR meta-analyses have derived equations estimating BMR from body mass that are specific to each sex and to age groups. Climate is another variable thought to influence BMR in humans, and it is possible that the modern pattern of BMR variation in humans represents, at least partially, a series of evolved responses to changes in global climate and migration into new climatic zones (Leonard et al., 2005; Wallace, 2005). Nevertheless, no existing predictive equations deal with this variable’s potential effects in a systematic manner that is applicable across human populations. According to a great deal of research, climate’s influence can be summarized as follows: when BMR is normalized for differences in FFM (henceforth BMRadj), tropical populations tend to have lower average BMR than temperate populations, who in turn have lower average BMR than those living in circumpolar regions or at high elevation (Christin et al., 1993; Galloway et al., 2000; Henry et al., 1987; Lawrence et al., 1988; Leonard et al., 2005; Minghelli et al., 1990; Rode and Shephard, 1995; Soares and Shetty, 1986; Spurr and Reina, 1988, 1989; Spurr et al., 1992; Ulijaszek and Strickland, 1991). As a general trend, BMR decreases with increasing mean annual temperature (TMEAN) when body mass is controlled for (Roberts, 1978). Additional support for this overall pattern comes from studies showing that standard reference equations based on a temperate sample (FAO/WHO/UNU, 1985; Schofield, 511 1985) tend to overestimate BMR in tropical populations by 3–13% (Cruz et al., 1999; Kashiwazaki et al., 1995; Leung et al., 2000; McNeill et al., 1987b; Nhung et al., 2005; Soares and Shetty, 1988; Soares et al., 1993; Spurr and Reina, 1988; Spurr et al., 1992, 1994), and underestimate BMR in circumpolar or high elevation populations by 2–10% (Beall et al., 1996; Leonard et al., 2005; Rode and Shephard, 1995; Snodgrass et al., 2005). Other studies, however, find good agreement between temperate-based estimates and measured BMR in nontemperate groups (Alam et al., 2005; Ferro-Luzzi et al., 1997; Galloway et al., 2000; Lawrence et al., 1988). Such findings support claims that variation in BMR between populations is better attributed to factors other than climate. In many tropical populations, the metabolic consequences of undernourishment or high-carbohydrate diets are cited as potential explanations for lower BMR relative to Europeans and North Americans (Shetty, 1996). With regard to circumpolar populations, elevated BMR is often attributed to high-protein diets (Kormondy and Brown, 1998), whereas morphological and behavioral traits are emphasized as adaptations to cold, as opposed to evolutionary explanations for the role of elevated BMR in maintaining body temperature (Beall and Steegmann, 2000; Kormondy and Brown, 1998). Contrary to these arguments against climate’s influence on BMR, however, temperate-based reference equations overestimate BMR by 3–12% in populations of partial or completely European descent consuming ‘‘western’’ diets, but that live in warmer subtropical climates (Piers et al., 1997; Valencia et al., 1994; van der Ploeg et al., 2001, 2002). Moreover, many circumpolar groups that exhibit higher BMR than expected from temperate standards do not consume an especially high-protein diet compared with adults in the United States (Leonard et al., 2005). Additional research suggests that BMRadj may not differ between marginally nourished and well nourished segments of the same population (Ferro-Luzzi et al., 1997; McNeill et al., 1987b; Shetty et al., 1990; Soares and Shetty, 1991; Spurr and Reina, 1988, 1989; see Shetty, 1999, for a review), suggesting that nutritional differences between populations may not affect BMR comparisons if body composition is controlled. An exception to this, however, would be in cases of semi-starvation, where physiological changes resulting from severe energy deficiency may also be related to a decline in BMR (Grande et al., 1958; Shephard, 1991; Shetty, 1999). Finally, research on mitochondrial DNA demonstrates an association between migration into current and recently cold/glacial climates and the presence of mutations that uncouple oxidative phosphorylation from ATP production (Mishmar et al., 2003; Wallace, 2005). Such mutations have the effect of directing a higher portion of food energy toward heat production rather than toward storage in ATP, possibly contributing to the maintenance of core body temperatures in colder environments. These mutations are more common in populations that have encountered glacial or arctic conditions over the past 50,000 years (i.e. circumpolar, European and indigenous North and South American) than in people living in areas of the Old World that have maintained tropical or temperate climates (Mishmar et al., 2003; Wallace, 2005). This may provide evidence for at least a partial genetic and evolutionary basis for the frequently observed correlation between BMR and climate in living humans. American Journal of Human Biology 512 A.W. FROEHLE If one accepts that climate may exert an important influence on human BMR, then the use of climate-inappropriate BMR equations to estimate DEE using the factorial method becomes potentially problematic. The main issue is that any initial errors in BMR are magnified in absolute terms in DEE estimates using the factorial method. Currently, no available equations deal with climate in a broadly applicable manner while also incorporating the other relevant variables of body mass/composition, sex and age. One current way of dealing with climate defines climate groups by latitude (e.g. tropical is defined as residing between the Tropics of Cancer and Capricorn), ignoring variation in climate that occurs even at the same latitude (consider, for example, the climates of San Diego, CA, Baghdad, Iraq, and Amdo, Tibet, all of which lie within one degree latitude of each other). Another approach is to incorporate continuous climate variables, such as TMEAN, into an analysis of BMR. One such study does examine the relationship between TMEAN and BMR, but does not include body composition as a predictor of BMR (Roberts, 1978), thereby ignoring an important factor known to vary between human groups living in different environments (Shephard, 1991). Also, TMEAN alone may be a poor indicator of climate, as it ignores other factors such as humidity and wind (FAO, 1957; FAO/WHO, 1973). The present study consists of a meta-analysis of BMR investigating the effects of several continuous climate variables, as opposed to broad latitude-based climate categories, meanwhile incorporating the influence of body mass/ composition, sex and age. This meta-analysis employs stepwise-regression in an attempt to elucidate a general pattern, should one exist, of the manner in which climate variables affect BMR, and expands beyond TMEAN to examine the effects of other aspects of climate. If any pattern does emerge, the study is set up such that it will reflect the relationship between climate and BMR on a global scale, applicable to human populations in general. Corresponding new predictive equations for the estimation of BMR will be derived, and will be compared with existing equations that do not incorporate climate variables in the manner used here. The consequences of including climate variables in estimating BMR will be discussed in terms of using the factorial method to derive DEE, with additional consideration of how these new equations might affect studies of living humans and of fossil hominins. Before describing the methods of this study, a brief review of commonly used and recently developed equations is warranted. EXISTING EQUATIONS FOR ESTIMATING BMR The number of equations discussed here is necessarily limited, because nearly 100 years of research has produced a large number of predictive equations for BMR (see Schofield, 1985, for a review). The most commonly used equations in human biology and biological anthropology in the recent past have been those of Kleiber (1961), the FAO/WHO/UNU (1985), also known as the Schofield (1985) equations, and the tropical-population-specific equations of Henry and Rees (1991). More recently developed, the Oxford Brookes equations (Cole and Henry, 2005; Henry, 2005) have not been widely used or validated (Weekes, 2007), but they deal with many of the problems associated with earlier meta-analyses; thus they provide a American Journal of Human Biology potentially better alternative to previous equations. All equations discussed here can be found in Appendix A. The oldest of the equations discussed here is the groundbreaking work of Kleiber (1961: referred to as K below). This equation is still commonly used, especially in fossil studies, and was derived from a taxonomically diverse sample of mammals. This study’s importance lies in its demonstration that body mass, not surface area, is the major determinant of BMR across mammals, and its establishment of the [3/4] exponent as the factor by which BMR scales to body mass, recently the subject of renewed interest (West and Brown, 2005). Despite its great influence on biology, this equation includes only two humans from North America, and thus does not account for any potential climate effects. Accordingly, the equation overestimates BMR in some subtropical populations by 14– 20% (Liu et al., 1995; Scalfi et al., 1993). The next oldest, and the most commonly used equations are from the FAO/WHO/UNU (1985), first developed in slightly different form by Schofield (1985) (referred to as FAO/S below). These equations are derived from a sample composed mainly of European and North American subjects from temperate climates, and present unique equations for each of 6 age divisions within each sex. This allows the investigator to estimate BMR from body mass where sex and age are known. The equations published in 1985 represent the latest output from a long-term program of the Food and Agriculture Organization (FAO) of the United Nations researching the energy needs of different populations worldwide. In early FAO investigations (1957), the effects of climate were considered, with the recommendation that energy expenditure estimates be reduced by 5% for every 108C increase in TMEAN over a temperate reference standard of 108C. A similar recommendation was made to elevate energetic estimates by 3% for every 108C drop in TMEAN from the reference standard (FAO, 1957). In a later report (FAO/WHO, 1973), however, climate’s effects were reconsidered, with the assertion ‘‘that there is no quantifiable basis for correcting the [basal] . . . energy requirements according to the climate.’’ The 1985 FAO/WHO/UNU report echoed the 1973 report, but recommended further study into the subject. The 1985 report also noted that a small sub-sample of Indian subjects exhibited average BMR 10% lower than the majority European/North American sample, but refrained from proposing climate correction factors. The FAO/S equations have been widely tested, and provide accurate BMR estimates in some colder temperate populations (Buccholz et al., 2001; Curtis et al., 1996; Henry et al., 1999; Lawrence et al., 1988; Seale and Conway, 1999; but see Müller et al., 2004); but, as noted above a large number of studies find them inaccurate with regard to tropical, circumpolar and warmer temperate populations. Criticisms of the FAO/S equations focus on a number of problems with sampling bias, including the fact that of roughly 6,000 males aged 10–60 years included in the study, more than half were members of the Italian military, a rather homogeneous group (Hayter and Henry, 1994; Shetty et al., 1996). Some have suggested that Italians as a population have abnormally high BMR on the whole (Henry, 2005; Schofield, 1985), but this view is based on old data. More recent work shows that the FAO/ S equations overestimate BMR in various groups of Italians (Censi et al., 1998; Maffeis et al., 1993; Scalfi et al., 513 CLIMATE AND BMR IN HUMANS Fig. 1. Geographic distribution of the un-weighted sample. 1993). It may be that the Italian portion of the FAO/S database is simply composed of inaccurate measurements. Other critiques focus on the sample’s lack of tropical subjects, which restricts the evaluation of climatic influences on BMR (Hayter and Henry, 1994; Henry and Rees, 1991; Shetty et al., 1996). To deal with the FAO/S climate limitations, Henry and Rees (1991: referred to as H&R below) produced age- and sex-specific equations similar to those of FAO/S, but derived from an entirely tropical sample. Their BMR estimates are 8% lower on average than those of FAO/S, and though not as extensively tested, the H&R equations provide accurate BMR estimates in some tropical subjects (Soares et al., 1993). But, like FAO/S, the H&R equations are limited by their geographically restricted sample, significantly underestimating BMR in Europeans by 5% (Soares et al., 1993). Less easily explained, the H&R equations also overestimate BMR by 6–8% in some tropical groups, while giving underestimates of 4–11% in others (Spurr et al., 1996b; Yamauchi and Ohtsuka, 2000). These equations also estimate BMR to within 0.5% in North Americans from the decidedly non-tropical climates of Philadelphia and Montreal (Soares et al., 1993). Thus, questions as to the accuracy of H&R remain. Much more recently, the Oxford Brookes BMR database was developed and analyzed to provide updated and more broadly applicable equations (Cole and Henry, 2005; Henry, 2005: referred to as OB below). This sample included a large number of subjects living over a wide geographic range, and although some of the same data used in the FAO/S equations were included, the Italian subjects were excluded as outliers. The primary analysis produced age- and sex-specific equations similar in approach to those of FAO/S and H&R. Further analysis focused on the relationship between age and BMR, integrating adult and juvenile data into a ‘‘seamless’’ approach to estimating BMR (Cole and Henry, 2005). In other words, rather than producing age-group-specific equations, this analysis aimed to produce a single equation incorporating the effects of age, which eliminated the increased error inherent at the margins of age categories in the former approach. Following this idea, a simpler seamless approach will be used in part in the present analysis. Again, the OB equations remain untested (Weekes, 2007). MATERIALS AND METHODS Published BMR studies were obtained using the ISI Web of Knowledge Internet search engine, with each of the following search terms: BMR, RMR, REE, basal metaboli*, resting metaboli*, resting energy expenditure, metaboli* (asterisks indicate truncated searches). The variety of search terms reflects the lack of standardization between studies, where appropriate BMR measurement methods are used but the variable is referred to as resting energy expenditure (REE) or resting metabolic rate (RMR). Standardized BMR values in humans are measured after a 10–12-h fast (i.e. postabsorptive), with the subject lying supine and relaxed, under thermoneutral conditions (20–248C). This is in contrast to the standard protocol for RMR/REE, which allows measurement after only a three-hour fast, thus including some energy expenditure associated with digestion which is excluded from BMR (Blaxter, 1989; Ulijaszek, 1995). Each study was screened for adherence to standard BMR protocol, regardless of how the authors labeled the variable. Studies were also screened to ensure that they used a measurement method validated against other proven methods (Alam et al., 2005; Borghona et al., 2000; Butler et al., 2004; González-Arévalo et al., 2003; Kato et al., 2002; McLellan et al., 2002; McNeill et al., 1987a; Murgatroyd et al., 1993; Stewart et al., 2005; Tissot et al., 1995). Where reported, data from women measured during the luteal phase of menstruation or taking oral contraceptives were excluded, because these factors may elevate BMR American Journal of Human Biology 514 A.W. FROEHLE TABLE 1. Characteristics of the two samples N (Total) Tropical Temperate Circumpolar Age (years) Male:female ratio Body mass (kg) FFM (kg) BMR (kcal/d) Absolute Latitude (8) Elevation (m) TMEAN (8C) LWCT (8C) HHIT (8C) MTR (8C) ATR (8C) Un-weighted Weighted 329 78 225 26 32.7 6 1.0 (3–97) 0.495:0.505 60.5 6 0.9 (12.2–125.1) 46.1 6 0.7 (9.8–92.7) 1445 6 14.9 (624–2972) 36.140 6 0.93 (1.293–70.637) 401.6 6 48.3 (0–5150) 14.3 6 0.5 (211.1–29.0) 225.0 6 1.3 (278.3–17.8) 40.7 6 0.4 (24.0–60.0) 45.6 6 0.8 (11.0–70.0) 26.3 6 0.4 (12.5–42.3) 10,512 3,012 7,182 318 35.3 6 0.2 (3–97) 0.458:0.542 62.2 6 0.2 (12.2–125.1) 45.9 6 0.1 (9.8–92.7) 1427 6 2.4 (624–2972) 33.910 6 0.17 (1.293–70.637) 274.5 6 4.9 (0–5150) 15.7 6 0.1 (211.1–29.0) 224.5 6 0.2 (278.3–17.8) 41.5 6 0.1 (24.0–60.0) 45.8 6 0.1 (11.0–70.0) 25.3 6 0.1 (12.5–42.3) All values are mean 6 SEM, range in parentheses. TMEAN, mean annual temperature; LWCT, lowest monthly windchill temperature; HHIT, highest monthly heat index temperature; MTR, maximum monthly temperature range; ATR, average monthly temperature range. (Anantharaman-Barr et al., 1990; Curtis et al., 1996; Diffey et al., 1997; Ferraro et al., 1992; Piers et al., 1997; Solomon et al., 1982, but see Piers et al., 1995). It should be noted that the majority of studies did not comment on these subject characteristics, and therefore may have included such women. Additionally, only data from normal, healthy subjects were included (e.g. control subjects in disease studies), and pregnant and lactating women were excluded. Where possible, data from obese subjects were excluded, but the manner in which the database was assembled (see below) makes it likely that at least some obese subjects were included in the overall sample. After screening, data from 159 different studies were used (see Appendix B) representing 103 different locations worldwide (see Fig. 1). All BMR data were converted to kcal/d, and corresponding data on FFM (kg), body mass (kg), age (y) and sex (female 5 0, male 5 1) were included. For each study’s measurement site(s), latitude, longitude, and elevation were obtained from a free online geographic database (http://www.heavens-above.com/countries.aspx) that compiles information from the United States Geological Survey and the United States National Imaging and Mapping Agency. Using these data, the nearest World Meteorological Organization (WMO) weather station for each site was located using an online database of the United States National Oceanic and Atmospheric Administration (http://www1.ncdc.noaa.gov/pub/data/ inventories/STNLIST-SORTED.TXT). Climate data for these weather stations are publicly available via the United States National Centers for Environmental Prediction’s Climate Prediction Center. Monthly summaries of data are maintained and made accessible online [http:// dss.ucar.edu/datasets/ds512.0/data/ (free registration required)] by the United States National Center for Atmospheric Research/University Corporation for Atmospheric Research. Weather stations were located an average of 14.5 km from each study site (measured by great circle distance), and within 45 km for 97 of the 103 measurement sites. The distance of 45 km was accepted as reasonable (i.e. climate data did not require independent verification), since for some study sites (e.g. Beijing, Tokyo, New York) measurement could have occurred this far from the weather station, but still within the same large metropolitan area. No studies provided details about where subjects came American Journal of Human Biology from within such metropolises, aside from naming the region broadly. Thus, a similar standard was applied to the entire data set. For six sites the nearest weather station lay outside of the 45 km boundary (range: 52–427 km); in these cases the weather station data were checked against other independent sources for consistency (Beall et al., 1996; Goldstein and Beall, 1990; Huq and Asaduzzaman, 1999; Snodgrass et al., 2005). Climate records for each site were obtained from January 1987 through November 2005, when this study’s data collection began. To standardize across studies and examine general climate patterns (as opposed to annual outliers), data across this entire period were used for each study site. For 46 sites, complete datasets of 227 months were available, and the majority of sites (77) had 192 months (16 years) of available data. Of the remaining 26 sites, 23 had only 6–15 years of data. These sparser datasets were not clustered geographically, however, so they were kept in the study. Three sites with 3 years of data were dropped from the study (not included in the totals above). Five climate variables were included. Following Roberts (1978), TMEAN was used, and was calculated by averaging all monthly mean temperatures from the available data. To expand the treatment of climate, extremes in temperature and the effects of humidity and wind were also of interest. Thus, for each site monthly low wind chill temperature (LWCT) and monthly high heat index temperature (HHIT) were obtained; the lowest extreme value of LWCT and the highest extreme value of HHIT for each site were used. Two variables expressing temperature range were also included by subtracting LWCT from paired HHIT values for each month. The mean of all such values for each dataset was calculated to arrive at average temperature range (ATR), and the maximum monthly temperature range was also obtained (MTR). Absolute latitude was included, as was membership in one of three latitude-based climate groups, defined using standard boundaries: tropical <23.4558 absolute latitude; temperate >23.4558 and <60.0008 absolute latitude; circumpolar >60.0008 absolute latitude. Elevation was included as a continuous variable and also as a categorical variable (0–1150 m, 1150–2300 m, >2300 m above sea level). See Table 1 for descriptive data on each dataset. CLIMATE AND BMR IN HUMANS Fig. 2. 515 Geographic distribution of the weighted sample. Potential caveats in the meta-analysis Two main issues relevant to this meta-analysis merit brief discussion. The first is that most studies included in the database do not report individual data, but rather means for groups of subjects. Thus, all of the data used here represent group means (where individual data were reported, means were calculated and incorporated into the database). This departs from more recent meta-analyses of BMR data (Cole and Henry, 2005; Henry and Rees, 1991; Henry, 2005), but was useful in that it allowed a considerable expansion of the sample from a geographical and climatic standpoint. Studies were scrutinized to ensure that all such group means included in the database came from closed groups. A group was considered closed when all relevant data came from only one sex, a single age group (<18 years, 18–50 years, and >50 years), and a single study locale. For every study, means for the smallest reported closed groups were used, resulting in an overall sample size of n 5 329 group means (breakdown by latitude: n 5 78 tropical, n 5 225 temperate, n 5 26 circumpolar). The group means used here each represent samples of between 2 and 521 individual subjects, with an average sample size of n 5 32. The wide variation in sample size represented by each group mean, and the use of group means in general, has the potential to artificially decrease the observed variance of the sample. In other words, a sample of 100 group means may have decreased variance compared with a sample of 100 individual measurements, which is relevant to the interpretation and validity of this study’s sample. To investigate whether this was a problem, standard error of the mean (SEM) for this study’s sample was compared with SEM reported for similarly sized samples of individuals. The basis for this approach lies in the relationship between variance (r2) and SEM (r/ n0.5), where samples of similar size with similar SEM will also have similar variance. This comparison showed no bias towards decreased variance in this study’s sample as compared with samples of individual subjects. As an additional precaution, however, two separate analyses were performed: one using the group means as individual data points, and a second, weighted approach based on the sample size represented by each group mean. In the weighted analysis, a group mean representing 100 subjects would be counted 100 times, whereas it would be counted only once in the un-weighted analysis. Figure 2 shows the geographical distribution of the weighted sample. The second potential caveat regards pooling data from widely dispersed populations that may live very different lifestyles. Such data compilation incorporates a number of variables that could confound the effects of climate on BMR, including body composition, ethnicity, nutritional status, varying work habits and exposure to the elements, and seasonal fluctuations in climate and caloric intake. Body composition (i.e. body fat percentage) varies with climate and between populations, and indeed some have suggested that the observed effects of climate on BMR are simply an artifact of body composition variation (Cunningham 1980, 1991; Nelson et al., 1992). This suggestion is based on the observation that adipose tissue has little to no metabolic activity and thus contributes little to BMR (Cunningham, 1980, 1991). Therefore, when comparing populations that vary in terms of body fat, the effects of other variables may be masked or artificially shown to be significant when body fat variation is not controlled. This is not a major problem for the present study because FFM is used as the primary body size variable (though a secondary analysis is conducted using body mass in place of FFM). Body fat is omitted from FFM, thus controlling for population-level differences in body composition and including only metabolically active tissue. Differences in body composition may underlie other possible confounders of climate’s effects on BMR, and thus American Journal of Human Biology 516 A.W. FROEHLE use of FFM to normalize BMR may minimize their statistical interference. For example, although Roberts (1978) uses body mass to normalize BMR and finds ethnic clines in the BMR/TMEAN relationship, other studies using FFM find that different ethnic groups living in similar climates have similar BMRadj (Christin et al., 1993; Henry et al., 1987; Lawrence et al., 1988; Minghelli et al., 1990; Soares and Shetty 1986; Spurr and Reina, 1988, 1989; Spurr et al., 1992; Ulijaszek and Strickland, 1991; males in Galloway et al., 2000). Other studies, however, find that ethnically different groups living in the same location do exhibit significantly different BMRadj (Galloway et al., 2000; Rode and Shephard, 1995), or that ethnically similar populations living in different climates nonetheless have similar BMRadj (Luke et al., 2000, 2002). These findings coupled with possible evidence for a genetic basis to at least some variation in BMR related to climate (Wallace, 2005) indicate that ethnicity and climate likely interact to produce average BMR in any population. Because the ethnicity of most subjects included here is unknown, these issues unfortunately cannot be tested using this sample. Differences in nutrition between populations should not confound climate’s influences, since many studies find no difference in BMRadj between well-nourished and undernourished subjects (Ferro-Luzzi et al., 1997; McNeill et al., 1987b; Shetty et al., 1990; Soares et al., 1991; Spurr and Reina, 1988, 1989; Spurr et al., 1992). Seasonality of climate likewise should not pose a major problem for this study, because many find no significant daily or seasonal variation in BMRadj in a variety of environments (Ategbo et al., 1995; Beall et al., 1996; Schultink et al., 1990; Spurr et al., 1994; Tohori et al., 1988). Plasqui et al. (2003), however, report a small (62.3% of the mean) but significant seasonal fluctuation in sleeping metabolic rate, with no corresponding change in FFM. A number of Japanese studies have also demonstrated seasonal variation in BMR, with summer lows and winter highs (Kashiwazaki, 1990), though only one controls for changes in body composition (Tashiro, 1961). Seasonality was impossible to control in the present study, because the season during which each subject’s BMR was measured was not often reported. Finally, lifestyle differences related to exposure to extreme conditions appear not to influence BMRadj (Rode and Shephard, 1995; Snodgrass et al., 2005; Yamauchi and Ohtsuka, 2000), nor do differences in level of physical activity (Armellini et al., 2000; Bingham et al., 1989; Gilliat-Wimberly et al., 2001; Pullicino et al., 1996; Smith et al., 1997; Taaffe et al., 1995). Based on each regression analysis, equations were derived that estimate BMR from any variables shown to have a significant effect on BMR. In addition to these equations, equation sets divided according to sex and age and similar to those presented in previous studies (FAO/S; H&R; OB) were derived using the significant independent variables. The present study’s equation sets differ in the way age groups are divided, using 18 years and 50 years as borders and resulting in only three age groups per sex (juveniles <18 years of age, reproductive-age adults 18–50 years of age, and older adults >50 years of age) as opposed to more in previous studies. Estimates of BMR using new and previously published equations were then compared for accuracy using two samples. One was the un-weighted sample of group means used in this study, which provided a test of the equations’ accuracy in populations. The other sample (n 5 463) consisted of all individual subject data from published reports included in this study’s sample, along with a set of individual data from the Yakut of Siberia, previously published only as group means (Snodgrass and Leonard, personal communication; Snodgrass et al., 2005). The frequency of predicted values within 65% and 610% of measured BMR in each sample was assessed for each equation, and was broken down by climate to examine inter-climate consistency in the equations. In addition, root mean square (RMS) error, which indicates the precision of an equation’s estimates (Freedman et al., 1997), was calculated for each equation. RESULTS See Table 2 for all regression results and significance. For the un-weighted sample using FFM as the body size variable, FFM alone was the primary predictor of BMR (P < 0.001, r2 5 0.776). With FFM and age as predictors, the equation improved (P < 0.001, r2 5 0.803), and improved further when FFM, age and TMEAN were all included (P < 0.001, r2 5 0.815). Finally, adding sex to FFM, age and TMEAN as predictors, the equation significantly improved (P < 0.001, r2 5 0.821). None of the other variables had a significant effect on BMR when the above four were included in the analysis. TABLE 2. Stepwise regression resultsa Dataset Un-weighted Size variableb FFM Statistical analysis Stepwise regression, with BMR as the independent variable, was used to analyze both the un-weighted (n 5 329; 78 [24%] tropical, 225 [68%] temperate, 26 [8%] circumpolar) and weighted (n 5 10,512; 3012 [29%] tropical, 7182 [68%] temperate, 318 [3%] circumpolar) samples. For each sample, two separate analyses were conducted, one using FFM as the body size variable, and the other using whole body mass. In addition to the body size variable, each analysis included numerical age, the climate variables (TMEAN, LWCT, HHIT, ATR, MTR), absolute latitude, latitude-based climate group, elevation, and elevation group. American Journal of Human Biology Body mass Weighted FFM Body mass a Significant variablesc r2 FFM FFM, age FFM, age, TMEAN FFM, age, TMEAN, sex Mass Mass, sex Mass, sex, age Mass, sex, age, TMEAN FFM FFM, age FFM, age, HHIT FFM, age, HHIT, sex Mass Mass, age Mass, age, sex Mass, age, sex, HHIT 0.776 0.803 0.815 0.821 0.612 0.730 0.798 0.827 0.781 0.813 0.829 0.831 0.619 0.751 0.826 0.836 Where BMR is the dependent variable. FFM included in analysis to the exclusion of body mass and vice versa. Significance for all variables P 0.001. b c 517 CLIMATE AND BMR IN HUMANS TABLE 3. New equations Dataset Un-weighted Eq. (1) Eq. (2) SET A SET B Weighted Equationa P r2 All All M <18 F <18 M 18–50 F 18–50 M >50 F >50 M <18 F <18 M 18–50 F 18–50 M >50 F >50 BMR 5 [17.4 (61.3)3FFM] 2 [2.4 (60.8)3A] 2 [3.8 (61.5)3TMEAN] 1 [50.6 (630.9)3SEX] 1 752 (661) BMR 5 [13.1 (60.93M] 1 [168 (626)3SEX] 2 [4.5 (60.8)3A] 2 [5.3 (61.4)3TMEAN] 1 791 (657) BMR 5 [22.4 (65.1)3FFM] 1 [1.7 (67.1)3TMEAN] 1 565 (6246) BMR 5 [17.7 (65.6)3FFM] 2 [1.9 (65.4)3TMEAN] 1 720 (6215) BMR 5 [23.3 (62.7)3FFM] 2 [4.1 (62.2)3TMEAN] 1 392 (6168) BMR 5 [12.3 (63.7)3FFM] 2 [3.6 (62.5)3TMEAN] 1 879 (6171) BMR 5 [9.8 (66.9)3FFM] 2 [10.9 (64.9)3TMEAN] 1 1124 (6401) BMR 5 [18.9 (65.7)3FFM] 2 [2.8 (65.9)3TMEAN] 1 529 (6249) BMR 5 [16.9 (64.1)3M] 2 [3.1 (66.9)3TMEAN] 1 703 (6231) BMR 5 [12.2 (63.8)3M] 2 [3.0 (65.3)3TMEAN] 1 779 (6198) BMR 5 [14.7 (61.7)3M] 2 [5.6 (62.3)3TMEAN] 1 735 (6131) BMR 5 [9.2 (62.1)3M] 2 [3.8 (62.2)3TMEAN] 1 852 (6137) BMR 5 [8.0 (63.9)3M] 2 [11.9 (64.1)3TMEAN] 1 1089 (6292) BMR 5 [10.6 (65.3)3M] 2 [4.9 (67.6)3TMEAN] 1 656 (6338) 0.003 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 0.001 0.821 0.827 0.859 0.766 0.755 0.370 0.641 0.643 0.838 0.760 0.742 0.474 0.723 0.395 All All M <18 F <18 M 18–50 F 18–50 M >50 F >50 M <18 F <18 M 18–50 F 18–50 M >50 F >50 BMR 5 [18.0 (60.2)3FFM] 2 [2.4 (60.1)3A] 2 [5.5 (60.3)3HHIT] 1 [26.7 (64.8)3SEX] 1 897 (616) BMR 5 [13.6 (60.13M] 2 [4.8 (60.1)3A] 1 [147 (64)3SEX] 2 [4.3 (60.3)3HHIT] 1 857 (616) BMR 5 [23.8 (60.7)3FFM] 1 [2.7 (61.5)3HHIT] 1 437 (671) BMR 5 [22.0 (60.8)3FFM] 1 [0.7 (60.9)3HHIT] 1 548 (650) BMR 5 [22.5 (60.4)3FFM] 2 [8.6 (60.5)3HHIT] 1 731 (635) BMR 5 [19.3 (60.6)3FFM] 2 [4.6 (60.5)3HHIT] 1 726 (637) BMR 5 [13.6 (60.9)3FFM] 2 [19.8 (61.2)3HHIT] 1 1547 (667) BMR 5 [18.9 (61.0)3FFM] 2 [11.1 (61.5)3HHIT] 1 925 (673) BMR 5 [18.5 (60.6)3M] 1 [0.9 (61.6)3HHIT] 1 543 (675) BMR 5 [15.0 (60.6)3M] 1 [1.0 (61.0)3HHIT] 1 597 (657) BMR 5 [14.2 (60.3)3M] 2 [9.8 (60.5)3HHIT] 1 1061 (631) BMR 5 [11.6 (60.3)3M] 2 [4.8 (60.5)3HHIT] 1 842 (632) BMR 5 [10.0 (60.9)3M] 2 [11.4 (61.5)3HHIT] 1 1224 (6106) BMR 5 [14.3 (60.8)3M] 2 [5.4 (61.6)3HHIT] 1 522 (691) <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 0.831 0.836 0.877 0.828 0.805 0.540 0.683 0.643 0.856 0.721 0.792 0.564 0.578 0.615 Group (s) Eq. (3) Eq. (4) SET C SET D a BMR is in kcal/d, FFM and body mass in kg, age in years, and TMEAN and HHIT in 8C. Sexes are assigned the following numerals: male 5 1, female 5 0. For each parameter, 95% confidence intervals are in parentheses. For the un-weighted sample using body mass as the body size variable, body mass alone was the primary predictor of BMR (P < 0.001, r2 5 0.612). With body mass and sex as predictors, the equation improved (P < 0.001, r2 5 0.730), and improved further when body mass, sex and age were all included (P < 0.001, r2 5 0.798). Finally, adding TMEAN to body mass, sex and age as predictors, the equation significantly improved (P < 0.001, r2 5 0.827). None of the other variables had a significant effect on BMR when the above four were included in the analysis. For the weighted sample using FFM as the body size variable, FFM alone was the primary predictor of BMR (P < 0.001, r2 5 0.781). With FFM and age as predictors, the equation improved (P < 0.001, r2 5 0.813), and improved further when FFM, age and HHIT were all included (P < 0.001, r2 5 0.829). Finally, adding sex to FFM, age and HHIT as predictors, the equation significantly improved (P < 0.001, r2 5 0.831). None of the other variables had a significant effect on BMR when the above four were included in the analysis. For the weighted sample using body mass as the body size variable, body mass alone was the primary predictor of BMR (P < 0.001, r2 5 0.619). With body mass and age as predictors, the equation improved (P < 0.001, r2 5 0.751), and improved further when body mass, age and sex were all included (P < 0.001, r2 5 0.826). Finally, adding HHIT to body mass, age and sex as predictors, the equation significantly improved (P < 0.001, r2 5 0.836). None of the other variables had a significant effect on BMR when the above four were included in the analysis. For each of the four analyses, a single equation was derived that predicted BMR from all of the significant variables. Un-weighted sample: Eqs. (1) and (2); weighted sample: Eqs. (3) and (4). Based on the regression results, each sample was also divided by sex, and each sex into three age categories. For each of these subdivisions, an equation was derived using the remaining significant body size and climate variables, resulting in four sets of equations similar to those of previous publications (unweighted sample: Equation Sets A and B; weighted sample: Equation Sets C and D). All new equations are found in Table 3 along with r2 values and significance. The predictive power of the new equations was compared with the K, FAO/S, H&R, and OB equations (Figs. 3 and 4). With regard to individuals, none of the new equations was particularly accurate, which was also true for the previously published equations. Accuracy to within 65% of measured BMR was particularly low, with the highest proportion of estimates in this range (0.41) coming from the new Eq. (1) and Set A, and the lowest from K (0.25). Within 610% of measured BMR, the best equation was Eq. (1) (0.67), with Set A and OB a close second (0.65). Again K was the least accurate with only 0.44 of predictions to within 610%. Between climate zones, the new equations were relatively consistent in their accuracy in temperate and circumpolar individuals (with the exceptions of Sets C and D), but were considerably less accurate in tropical individuals. Equation (2), for example, was equally accurate in temperate and circumpolar individuals, but accurate 0.20 less often in tropical individuals. None of the previous equations demonstrated this much inconsistency between climates, with the OB equations having an average between-climate discrepancy of only 0.07. Equation Set C, however, had the lowest average discrepancy in accuracy between climates of just 0.05, both within 65% and 610%. American Journal of Human Biology 518 A.W. FROEHLE Fig. 3. Predictive accuracy of equations in a sample of individuals. Bars represent the proportion of estimates for each equation within 65% or 610% of measured BMR. The lower two graphs divide the sample by climate to show which equations provide the most consistent results from region to region. Fig. 4. Predictive accuracy of equations in a sample of populations (group means). Bars represent the proportion of estimates for each equation within 65% or 610% of measured BMR. The lower two graphs divide the sample by climate to show which equations provide the most consistent results from region to region. The findings on prediction accuracy in populations are quite different from those in individuals. Overall accuracy was much higher, with all of the new equations estimating BMR to within 65% over half of the time (highest: Set A, 0.59). Of the previous equations, both FAO/S and OB were near the 0.50 mark (0.49 and 0.51, respectively), while again, K was accurate least frequently (0.29). To within 610% of measured BMR, the new equations’ accuracy ranged from 0.84 to 0.88 (highest: Set A), whereas the previous equations’ values were not as high (K: 0.50; FAO/S: 0.75; H&R: 0.77; OB: 0.81). More importantly, the new equations were substantially more consistent between climate regions when used with populations, as compared with the previous equations. To within 65%, the most consistent equation was new Eq. (3) (0.03 average discrepancy between climates), although K came in a close second (0.05). The remaining new equations had average between-climate discrepancies of 0.05– 0.17, whereas the other previous equations ranged from 0.11 to 0.29. To within 610% of measured BMR, the most consistency came from new Equation Set D (0.01), whereas the remaining new equations had between-climate discrepancies between 0.03 and 0.09. The previous equations were far more inconsistent here, with betweenclimate discrepancies ranging from 0.09 to 0.26. In the individual sample, mean error, a measure of overall estimation accuracy, was slightly lower on average in the new equations (range: 263 kcal/d to 110 kcal/d) than in the previous equations (range: 2130 kcal/d to 122 kcal/ d) (see Fig. 5). The lowest-magnitude mean error was for Eq. (3), which was 27 kcal/d, whereas the highest came from K (2130 kcal/d). When these two equations were excluded, both the new and old equations had very similar average absolute mean error (29 kcal/d vs. 31 kcal/d, respectively). In populations, again the situation was different, with the new equations showing considerably more accurate mean error (range: 21 kcal/d to 123 kcal/d than the previous equations (range: 262 kcal/d to 72 kcal/d). The lowest-magnitude mean error was shared by Eq. (2) and Set B (21 kcal/d), whereas the largest was from H&R (72 kcal/d). The average absolute mean error for the new equations was 10 kcal/d, and 42 kcal/d in the previous equations. Root mean square (RMS) error is a measure of the precision with which an equation estimates a dependent variable. Theoretically, 68% of all estimates should fall within 61 RMS error of the actual value, and 95% within 62 RMS errors. Smaller RMS error values indicate American Journal of Human Biology 519 CLIMATE AND BMR IN HUMANS DISCUSSION Fig. 5. Mean error 6 1 root mean square (RMS) error for the equations’ BMR estimates in both the individual and population samples. Mean error is the average of all raw residual values, and indicates whether or not each equation contains an overall positive or negative bias. RMS error indicates the magnitude of difference from zero for a typical residual. In general, 68% of all residuals fall within 61 RMS error of zero, and 95% within 2 RMS errors (Freedman et al., 1997). Smaller RMS error values indicate a higher degree of precision with respect to an equation’s estimates. greater precision, whereas higher values mean a regression is less precise with regard to a particular sample. For the individual sample, the largest RMS error value was for K (286 kcal/d), whereas the lowest (183 kcal/d) was shared by Equation Sets A and B. None of the other equations, new or old, however, differed from this low value by more than 25 kcal/d (FAO/S), suggesting that with the exception of K, all of these equations have relatively the same level of precision with regard to estimates for individuals (see Fig. 5). In the population sample, again K had the highest RMS error (212 kcal/d), whereas the lowest belonged to Equation Set A (105 kcal/d-Set B was a close second at 107 kcal/d). Within the other new equations, RMS errors were between 7 and 13 kcal/d higher than this low value, whereas in the previous equations (excluding K), this range was between 21 and 51 kcal/d. This suggests that the new equations may be slightly more precise with regard to populations, but it may partially be an artifact of using the sample from which the new equations were derived to test their precision. In any case, with the exception of K, the new and previous equations again appear to have relatively similar degrees of precision in this sample. The above analysis demonstrates that climate variables can be significant predictors of BMR, and that their inclusion in equations can improve the accuracy of BMR estimates, at least in populations. Although idiosyncratic variation likely overpowers any effects of climate in the analysis of individuals, it appears that factorial method investigations of DEE at the population level may benefit from the inclusion of climate factors, especially when BMR is estimated rather than measured. The overall effect of climate found here is that for every 18C drop in TMEAN, BMR increases by roughly 4–5 kcal/d, when controlling for the effects of body size, age and sex. A similar 4–5 kcal/d increase in BMR occurs per 18C decrease in HHIT, when body size, age and sex are also controlled. This study’s climate-based adjustments in BMR fall in the lower range of those which the earliest report of the FAO (1957) recommends (64–8 kcal/d per 18C above or below TMEAN of 108C: see FAO, 1957, pp 24–26, 54). The biological meaning of the significance of either TMEAN or HHIT is not clear. Both variables are highly correlated with one another, and with the majority of the other climate and geographic variables included in the study (see Table 4). Indeed, there is so much significant correlation between the different climate variables that it is impossible to tease out what might be underlying the overall pattern as it relates to BMR. There are highly significant correlations between absolute latitude and all of the climate variables, and the highest r-value is between absolute latitude and TMEAN in both the un-weighted and weighted samples. The latitude/HHIT relationship, although highly significant in both samples, is not as close to unity, and other variables that were not significant in either stepwise regression analysis have higher r-values in correlation with latitude. Thus, examination of the correlation results does not do much to explain why TMEAN and HHIT are significant predictors of BMR whereas other variables are not. More importantly, because TMEAN was the only significant climate variable in one analysis, and HHIT the only one in the other, this study does not answer the question of TABLE 4. Pearson correlation for climate and geographical variables* ABSLAT Elevation Un-weighted Elevation 20.223** TMEAN 20.865** LWCT 20.771** HHIT 20.572** MTR 0.526** ATR 0.635** Weighted Elevation 20.238** TMEAN 20.888** LWCT 20.731** HHIT 20.478** MTR 0.453** ATR 0.662** TMEAN LWCT HHIT MTR 20.108 NS 20.070 NS 0.875** 20.083 NS 0.700** 0.412** 0.172*** 20.668** 20.910** 20.157*** 0.085 NS 20.744** 20.918** 20.257** 0.900** 0.023**** 0.024**** 0.862** 20.071** 0.583** 0.287** 0.074** 20.621** 20.900** 20.030**** 0.064** 20.756** 20.895** 20.104** 0.825** ABSLAT, Absolute latitude; TMEAN, mean annual temperature; LWCT, lowest monthly windchill temperature; HHIT, highest monthly heat index temperature; MTR, maximum monthly temperature range; ATR, average monthly temperature range. NS, Not significant. * Pearson correlation r-values. ** Significant at level of P < 0.001. *** Significant at level of P < 0.01. **** Significant at level of P < 0.05. American Journal of Human Biology 520 A.W. FROEHLE TABLE 5. Comparison of new BMR and DEE estimates to previous estimates and measurements Reference Leonard et al., 1995 Locality (population) Sex Age (y) Body mass (kg) TMEANa PALb BMR1c BMR2d BMR3b DEE1c DEE2d DEE3b Salcedo, Ecuador (highland) M F M F M F M F M F M F M F 32 40 49 34 18–50 18–50 18–50 18–50 32 31 36 33 10–18 10–18 61.3 55.7 55.6 47.8 59.6 51.8 46.0 41.0 53.9 51.0 72.4 64.7 45.1 42.5 12.9 12.9 24.9 24.9 20.0 20.0 19.6 19.6 21.0 21.0 21.0 21.0 26.1 26.1 2.38 1.96 1.58 1.62 2.00 1.50 1.68 1.56 1.48 1.59 1.39 1.53 1.79 1.66 1,601 1,252 1,529 1,226 1,591 1,394 1,383 1,099 1,507 1,266 1,749 1,417 1,440 1,265 n/a n/a n/a n/a n/a n/a n/a n/a 1,634 1,288 1,892 1,302 n/a n/a 1,564 1,315 1,413 1,197 1,499 1,253 1,301 1,155 1,533 1,325 1,805 1,451 1,384 1,219 3,127 2,145 2,188 1,916 3,186 2,085 2,319 1,712 2,129 1,794 2,363 2,026 2,605 2,105 3,808 2,458 2,415 1,992 n/a n/a n/a n/a 2,387 2,019 2,609 1,973 n/a n/a 3,722 2,577 2,233 1,939 2,998 1,880 2,186 1,802 2,269 2,107 2,509 2,220 2,477 2,024 Jipijapa, Ecuador (coastal) Leonard and Robertson, 1997 Leonard et al., 1997 Gamboa and Garcia, 2007 Eastern Paraguay (Ache) Kalahari Desert, Botswana (!Kung) Surinda area, Russia (Evenki) Surinda area, Russia (Russian) Calakmul, Mexcio a Obtained from the UCAR database according to this study’s methods, except for Ache and !Kung. Ache and !Kung estimated from published temperature ranges (Hill et al., 1984; Bentley, 1985). b As estimated using this study’s Equation Set B for BMR, with PAL from previous studies used for DEE estimates. c As estimated using FAO/S for BMR in the original studies. All reported values converted to kcal/d. d As measured in the original studies. All reported values converted to kcal/d. whether climate-related variation in BMR associates more with climate norms or climate extremes. This leaves questions as to the best climate variable to use in BMR prediction (see FAO, 1957; FAO/WHO, 1973), but does to some extent support past uses of TMEAN as a BMR predictor (FAO, 1957; Roberts, 1978). Moreover, for the sake of convenience, TMEAN is a more widely accessible parameter than some of the other climate variables, with particular regard to fossil hominins and extant human groups living in remote regions (i.e. those areas not covered by WMO meteorological stations). In general, the results of accuracy testing here show that when attempting to develop broad models of DEE in populations, the use of BMR equations that include climate variables may indeed produce substantial differences in estimates as compared with equations that do not. In addition to greater overall accuracy, this study’s new equations are considerably more consistent between populations living in different climate regions. This is important to consider when comparing subsistence strategies and nutritional status among various living human groups, or in comparisons of various groups to established reference standards. The influence of climate is also important to studies of adaptation and competition in fossil hominins, where arguments using energetics are becoming increasingly important (e.g. Aiello and Wheeler, 2003; Churchill, 2006; Sorensen and Leonard, 2001; SteudelNumbers et al., 2006). To demonstrate the manner in which these new climateinclusive equations may alter DEE estimates in both living and fossil humans, two subsequent analyses were conducted. Both studies used Equation Set B as an example, both because of the set’s relatively high degree of accuracy and precision, and because the equations predict BMR from the most easily obtained variables (body mass and TMEAN, requiring age group rather than numerical age). First, DEE in several recently studied subsistence-level populations (Gamboa, and Garcia, 2007; Leonard and Robertson, 1997; Leonard et al., 1995, 1997) was re-estimated using Equation Set B and data available in the original publications (see Table 5). New DEE estimates were compared with previous values using FAO/S to estimate BMR, and were also compared with DEE measureAmerican Journal of Human Biology ments where available (see Fig. 6). Second, BMR and DEE were estimated for hypothetical average male and average female early Homo sapiens, living in three different climate zones based on this study’s living human data: HOT corresponds to tropical, MILD to temperate, and COLD to circumpolar/glacial. Fossil body mass and PAL data were drawn from the literature (see Table 6), and Equation Set B’s results were compared with previous equations’ estimates (see Fig. 7). In living humans, the new equations in general provide different BMR values than FAO/S, which also lead to different estimates for DEE. The largest discrepancies between current and past estimates of DEE are 19% and 20% in highland Ecuadorians, where the new estimates are 432–595 kcal/d higher than using FAO/S. Compared with measured DEE for this population, new estimates differ by only 86–119 kcal/d, or 2–5%. This runs counter to the idea that good BMR estimates will only improve DEE estimates by 10% (Durnin, 1990), and provides support for the use of these equations in living humans. A difference of 500 kcal/d is roughly equivalent to daily lactation costs in some subsistence-level populations (Butte et al., 1997), illustrating that the magnitude of such differences could have important consequences for the interpretation of DEE estimates. A similarly large discrepancy (17%; 313 kcal/d) is found in Evenki (herders) women, and again, the new DEE is far more similar to the measured value (4% difference; 88 kcal/d). The remaining differences in predicted values using the new and previous equations are somewhat more modest (on average 6%; 125 kcal/d; range of 23–205 kcal/d), and in one case (coastal Ecuadorean males) the previous DEE estimate is actually 6% closer to the measured value than the new estimate. Even so, this analysis suggests that at least in some cases, the inclusion of climate variables can have important consequences for estimating population-level DEE values and for the study of energy balance. Further improvements in DEE estimates might come through the use of FFM instead of body mass as the body size variable, which would better control for regional variation in body composition. The analysis of hypothetical early Homo sapiens suggests that the systematic incorporation of climate varia- CLIMATE AND BMR IN HUMANS 521 Fig. 7. Estimates of BMR and DEE in male and female early Homo sapiens using the new Equation Set B and the four previously published equations. Three different climate scenarios are used with Equation Set B, based on average TMEAN for tropical (HOT), temperate (MILD) and circumpolar (COLD) groups in this study’s sample. Values above each column are DEE estimates in kcal/d. Body mass, PAL, and temperature values are shown in Table 6 along with references. Fig. 6. Comparison of past DEE results of factorial method studies with new results using this study’s BMR Equation Set B. See Table 5 for references and data. Percent differences were obtained by dividing new DEE estimates by previous estimates: (DEE3/DEE1)-1. New DEE values were also compared with measured DEE, where available, in the same manner: (DEE3/DEE2)-1. Absolute differences in DEE were obtained by subtracting previous values from new estimates, whether the previous values were estimates: (DEE3-DEE1); or measurements: (DEE3-DEE2). TABLE 6. Data used for BMR and DEE estimates in early Homo sapiens a Body mass (kg) PALb TMEAN (HOT) (8C)c TMEAN (MILD) (8C) TMEAN (COLD) (8C) M F 65.0 1.84 54.0 1.53 25.0 14.0 26.0 a Average body mass for early Homo sapiens from McHenry (1992). Average physical activity level (PAL) for !Kung and Ache foragers from Leonard and Robertson (1997). c Temperatures derived from modern sample used in this study’s analyses. TMEAN (HOT) is mean of tropical, TMEAN (MILD) is mean of temperate, and TMEAN (COLD) is mean of circumpolar. b bles into energetics estimates in fossil hominins may be important. The advantage of the new equations is the ability to account for the effects of climate using a single model. The previous equations can only provide a single estimate for any body mass value, regardless of geographic origin. Correspondingly, the new and old equations’ estimates differ considerably. For example, com- pared to this study’s model, K overestimates DEE in females from all three climate regions, from a low of 34 kcal/d in COLD, to a high of 215 kcal/d in HOT. H&R is the opposite, underestimating female DEE by 32 kcal/d in HOT, up to 213 kcal/d in COLD. Both FAO/S and OB provide reasonably similar estimates to the new equations for females in HOT and MILD climates (within 50 kcal/d), but underestimate DEE in COLD-climate females by 150 kcal/ d. In males, all four previous equations underestimated DEE in COLD, from a low of 93 kcal/d (FAO/S) to a high of 338 kcal/d (H&R). In MILD-climate males, most of the previous equations underestimated DEE by 18 kcal/d (K) to 132 kcal/d (OB), whereas FAO/S provided a DEE estimate higher than that of Equation Set B by 113 kcal/d. In males from the HOT climate, H&R gave a quite similar DEE estimate to Equation Set B (219 kcal/d), whereas the others overestimated DEE (63 kcal/d in OB, to 226 kcal/d in FAO/S). The consequences of such discrepancies for studies of fossil hominin energy ecology can be demonstrated by considering that FAO/S, for example, would predict that a male and female pair living in glacial Upper Pleistocene Europe would require the same amount of energy each day, 5,046 kcal/d, as a similarly sized couple in East Africa. Meanwhile, using climate data and Equation Set B provides a slightly higher estimate in Europe of 5,271 kcal/d, and a much lower value for tropical East Africa of 4,771 kcal/d. Not only do both values differ from FAO/S, they differ from one another by the substantial figure of 500 kcal/d. In terms of studying foraging efficiency, the availability of energy for reproduction, and other such comparisons between populations, the incorporation of climate’s effects on BMR can provide a substantially different picture than exists without a consideration of climate. This holds both in living populations and as applied to fossil hominins. This study suggests that in the future, where BMR cannot be measured, assessments of energy expenditure may benefit from the incorporation of climate variables in preAmerican Journal of Human Biology 522 A.W. FROEHLE dicting BMR. The new equations presented here provide a systematic way to incorporate climate’s effects on BMR variation, so that different populations can be compared using the same methods and incorporating the same underlying assumptions. Given the large inaccuracies that can result from using previous equations such as those of the FAO/WHO/UNU (1985)/Schofield (1985), improved estimates using climate variables could prove very useful to understanding variation in human energy expenditure. ACKNOWLEDGMENTS I thank Margaret J. Schoeninger for helpful comments and advice. I also thank Josh Snodgrass and Bill Leonard for their comments, and for sharing their data on the Yakut of Siberia. Josh Snodgrass and an anonymous reviewer also provided very helpful comments. Climate data were provided by the Data Support Section of the Scientific Computing Division at the National Center for Atmospheric Research. NCAR is supported by grants from the National Science Foundation. 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Age (y) Males Females Kleiber (1961) (KLE) BMR 5 703(M) FAO/WHO/UNU (1985) (FAO) <3 BMR 5 59.5(M) 2 30.3 BMR 5 58.3(M) 2 31.1 3–10 BMR 5 22.7(M) 1 504.1 BMR 5 20.3(M) 1 485.7 10–18 BMR 5 17.7(M) 1 657.9 BMR 5 13.4(M) 1 692.3 18–30 BMR 5 15.1(M) 1 691.9 BMR 5 14.8(M) 1 486.4 30–60 BMR 5 11.5(M) 1 872.7 BMR 5 8.12(M) 1 845.2 >60 BMR 5 11.7(M) 1 609.0 BMR 5 2.76(M) 1 658.2 Henry and Rees (1991) (H&R) 3–10 BMR 5 27.0(M) 1 403.5 BMR 5 15.1(M) 1 589.1 10–18 BMR 5 20.1(M) 1 506.9 BMR 5 11.2(M) 1 705.0 18–30 BMR 5 13.4(M) 1 668.9 BMR 5 11.5(M) 1 612.1 30–60 BMR 5 11.0(M) 1 754.9 BMR 5 11.5(M) 1 584.8 Oxford Brookes (Henry, 2005) <3 BMR 5 61.0(M) 2 33.7 BMR 5 58.9(M) 2 23.1 3–10 BMR 5 23.3(M) 1 514 BMR 5 20.1(M) 1 507 10–18 BMR 5 18.4(M) 1 581 BMR 5 11.1(M) 1 761 18–30 BMR 5 16.0(M) 1 545 BMR 5 13.1(M) 1 558 30–60 BMR514.2(M) 1 593 BMR 5 9.74(M) 1 694 >60 BMR 5 13.5(M) 1 514 BMR 5 10.1(M) 1 569 0.75 Terms converted so that all BMR values are in kcal/d. Body mass (M) is in kilograms. TABLE B1. Geographic, climate and demographic details of this study’s sample with references. Locality Latitude Longitude Elevation TMEAN HHIT Nu (M,F) Adelaide, Australia 234.933 138.600 72 17.0 41.7 6 (4,2) Adelaide, Australia Alderly Park, England Aldershot, England Anaktuvuk Pass, AK Ann Arbor, MI Auckland, New Zealand Austin, TX 234.933 138.600 53.258 22.995 51.247 20.761 68.143 2151.736 42.271 283.726 236.867 174.767 30.267 297.743 72 172 76 683 261 13 163 17.0 10.2 10.1 28.8 10.5 15.6 20.4 41.7 32.8 33.3 29.4 43.9 30.6 47.2 2M 2M 2M 1M 4 (2,2) 2F 5 (4,1) Nw (M,F) Age class* Reference(s) 119 (95,24) 2 24 M 16 M 34 F 6M 162 (70,92) 48 F 146 (109,37) 3 2 2 2 1 2 2 Clark et al., 1993; Smith et al., 1997; van der Ploeg et al., 2001; van der Ploeg et al., 2001 Smith et al., 1999 Goldberg et al., 1995 Ulijaszek and Strickland, 1991 Milan et al., 1962 Katch et al., 1990 Rush et al., 1999 Broeder et al., 1992; Wilmore et al., 1998 Lemmer et al., 2001 Lemmer et al., 2001 Soares et al., 1993; Piers et al., 1995; Ferro-Luzzi et al., 1997; Borgonha et al., 2000; Sathyaprabha, 2000 Davies et al., 1997 Livingstone et al., 1991 Seale and Conway, 1999 Snodgrass et al., 2005 Calloway and Zanni, 1980 Treuth et al., 1998 Hunter et al., 2001 Gower et al., 2000 Fukagawa et al., 1990; Roberts et al., 1991; Grinspoon et al., 1998 Fukagawa et al., 1990; Bathalon et al., 2001 Van Pelt et al., 1997; Van Pelt et al., 2001 Van Pelt et al., 1997; Van Pelt et al., 2001 Dionne et al., 2004 Dionne et al., 2004 Spurr et al., 1992 Spurr et al., 1994; Dufour et al., 1999 Baltimore, MD Baltimore, MD Bangalore, India 39.290 39.290 12.983 276.613 276.613 77.583 2 2 917 13.1 13.1 24.4 45.6 45.6 41.1 Beijing, China Belfast, Northern Ireland Beltsville, MD Berdygestiakh, Russia Berkeley, CA Birmingham, AL Birmingham, AL Birmingham, AL Boston, MA 39.900 116.413 54.583 25.933 39.035 276.908 62.117 130.633 37.872 2122.272 33.521 286.803 33.521 286.803 33.521 286.803 42.358 271.060 59 5 32 161 56 173 173 173 11 13.3 9.6 13.1 25.6 14.6 17.2 17.2 17.2 10.9 47.2 28.3 45.6 36.7 37.8 55.0 55.0 55.0 40.0 2 (1,1) 2 (1,1) 2 (1,1) 2 (1,1) 1M 2F 1F 1F 3 (2,1) 12 (6,6) 32 (16,18) 69 (41,28) 125 (50,75) 6M 24 50 19 64 (38,26) 1 2 2 2 3 1 2 3 2 Boston, MA 42.358 271.060 11 10.9 40.0 3 (1,2) 70 (24,46) 3 Boulder, CO 40.015 2105.270 1646 10.5 38.3 4 (2,2) 96 (71,25) 2 Boulder, CO 40.015 2105.270 1646 10.5 38.3 5 (2,3) 106 (66,40) 3 Burlington, VT Burlington, VT Call, Colombia Call, Colombia 44.476 44.476 3.447 3.447 273.213 273.213 276.516 276.516 68 68 745 745 8.6 8.6 24.2 24.2 43.3 43.3 39.4 39.4 1F 1F 16 (8,8) 2F 19 F 12 F 528 (339,189) 135 F 2 3 1 2 2 (1,1) 16 (9,7) 2 (1,1) 19 (9,10) 15 (11,4) 259 (156,103) 2 3 2 APPENDIX B American Journal of Human Biology 528 A.W. FROEHLE TABLE B1. (Continued) Locality Cambridge, England Latitude Longitude Elevation TMEAN HHIT Nu (M,F) Nw (M,F) Age class Reference(s) Prentice et al., 1986; Bingham et al., 1989; Goldberg et al., 1993; Goldstone et al., 2002 Beer et al., 1989 Kashiwazaki et al., 1995 Luke et al., 2004 Lazzer et al., 2003 Meunier et al., 2005 Pratley et al., 1994 Thomas et al., 1994 Astrup et al., 1996; Klausen et al., 1997 McCrory et al., 1998 Kriketos et al., 2000 Burke et al., 1993; Cordain et al., 1997 Luhrmann et al., 2002 Kinabo and Durnin, 1990; Lawrence et al., 1990 Arvidsson et al., 2005 Pullicino et al., 1996 Nhung et al., 2005 Curtis et al., 1996 Valencia et al., 1994; Haggarty et al., 1997 Li et al., 1999 Butte et al., 2001; Butte et al., 2003 Luke et al., 2004 Luke et al., 2000 Rode and Shephard, 1995 Rode and Shephard, 1995 Rode and Shephard, 1995 Peng et al., 2005 Peng et al., 2005 Stettler et al., 1998 Lawrence et al., 1988; Singh et al., 1989; Minghelli et al., 1990; Diaz et al., 1991; Frigerio et al., 1992; Benedek et al., 1995; Heini et al., 1996 Benedek et al., 1995 Illner et al., 2000 Singhal et al., 2002 Singhal et al., 1997 Henry et al., 2005 Aleman-Mateo et al., 2006 Minghelli et al., 1990 Dolezal and Potteiger, 1998 Lof and Forsum, 2006 Kerckhoffs et al., 1998; Spaanderman et al., 2000 Kerckhoffs et al., 1998 Ategbo et al., 1995 Alam et al., 2005 Luke et al., 2000 Diffey et al., 1997; Piers et al., 1997 Sanchez-Castillo et al., 2001 Keys et al., 1973 Keys et al., 1973 Cagnacci et al., 2006 Schultink et al., 1990 Jobin et al., 1996; Boivin et al., 2000 Scalfi et al., 1993; Marra et al., 1998; Rizzo et al., 2005 Rizzo et al., 2005 Buchowski et al., 2000 Buchowski et al., 2000 Segal and Dunalf, 1990; Myerson et al., 1991; Ratheiser et al., 1998; Wang et al., 2005 Garby et al., 1987 Puggaard et al., 2002 Henry et al., 1999; Henry et al., 2005 Henry et al., 1989; Hayter and Henry, 1993; Henry et al., 1999 52.205 0.144 40 9.4 32.8 5 (1,4) 62 (3,59) 2 42.358 217.483 41.850 45.783 45.783 38.981 38.952 55.667 271.106 269.467 287.650 3.083 3.083 276.937 292.334 12.583 11 4086 178 391 391 28 232 0 10.9 6.1 11.3 11.9 11.9 13.1 12.8 9.5 40.0 31.1 47.2 37.2 37.2 45.6 43.3 33.3 2M 2 (1,1) 1M 2 (1,1) 2 (1,1) 1M 1M 3 (1,2) 17 M 19 (7,12) 172 M 50 (23,27) 70 (35,35) 13 M 7M 341 (78,283) 2 2 2 1 3 3 2 2 Davis, CA Denver, CO Fort Collins, CO 38.545 2121.739 39.739 2104.984 40.585 2105.084 15 1596 1525 16.5 10.5 10.5 47.8 38.3 38.3 2 (1,1) 2 (1,1) 4 (1,3) 19 (11,8) 94 (49,45) 37 (14,23) 2 2 2 Glessen, Germany Glasgow, Scotland 50.583 55.862 8.650 24.245 167 68 10.2 9.0 35.0 27.8 2 (1,1) 3F 286 (107,179) 153 F 3 2 Goteborg, Sweden Guarda Mangla, Malta Hanol, Vietnam Headington, England Hermosillo, Mexico 57.717 11.967 35.891 14.492 21.033 105.850 51.763 21.210 29.067 2110.967 3 1 22 76 195 8.9 19.4 24.9 10.5 25.3 31.7 46.1 51.1 33.3 60.0 2 (1,1) 4F 4 (2,2) 2F 4M 33 (17,18) 50 F 188 (98,90) 12 F 37 M 1 2 2 2 2 Hong Kong, China Houston, TX Ibadan, Nigeria Igbo-Ora/Idere, Nigeria Igloolik, Canada Igloolik, Canada Igloolik, Canada Kagoshima, Japan Kagoshima, Japan Keneba and vicinity, Gambia Keneba and vicinity, Gambia 22.283 29.763 7.388 7.458 69.400 69.400 69.400 31.600 31.600 13.329 13.329 114.150 295.363 3.896 3.267 281.800 281.800 281.800 130.550 130.550 216.015 218.015 89 15 239 148 1 1 1 89 89 32 32 23.8 20.8 25.5 25.5 211.1 211.1 211.1 19.0 19.0 26.6 26.6 50.0 44.4 42.8 42.8 25.0 25.0 25.0 42.2 42.2 47.8 47.8 1F 4F 2 (1,1) 2 (1,1) 2 (1,1) 6 (3,3) 3 (2,1) 1F 1F 1F 9 (5,4) 19 F 140 F 996 (475,521) 89 (50,39) 16 (14,2) 23 (11,12) 7 (5,2) 12 F 16 F 7F 189 (119,70) 2 2 2 2 1 2 3 2 3 1 2 Keneba and vicinity, Gambia Kiel, Germany Kingston, Jamaica Kingston, Jamaica Kuala Lumpur, Malaysia Las Terrazas, Cuba Lausanne, Switzerland Lawrence, KS, US Linkoplng, Sweden Maastricht, Netherlands 13.329 54.550 18.000 18.000 3.167 22.764 46.533 38.972 58.417 50.850 216.015 9.167 276.800 276.800 101.700 283.242 6.667 295.235 15.617 5.683 32 24 42 42 64 51 857 259 33 64 26.6 10.4 28.3 28.3 28.3 25.5 11.2 13.1 6.9 10.6 47.8 30.6 44.4 44.4 50.6 39.4 35.6 42.8 34.4 38.3 1M 2 (1,1) 2 (1,1) 1M 1F 2 (1,1) 1M 3M 1F 2 (1,1) 28 M 26 (13,13) 31 (17,14) 16 M 51 F 10 (5,5) 16 M 30 M 23 F 23 (11,12) 3 2 1 2 1 3 2 2 2 2 50.850 10.350 23.328 41.879 237.817 19.400 44.962 44.962 44.667 6.930 45.500 40.833 5.883 1.117 90.675 287.843 144.967 299.150 293.179 293.179 10.917 1.717 273.583 14.250 64 228 3 190 58 2224 247 247 25 64 113 0 10.6 27.5 26.5 11.3 16.1 16.6 9.3 9.3 14.5 28.1 7.0 16.8 38.3 48.3 49.4 47.2 41.7 41.7 42.8 42.8 42.8 51.7 38.3 44.4 1M 1F 1F 1M 3M 1F 1M 1M 1F 1F 2M 3F 9M 34 F 37 F 65 M 108 M 34 F 168 M 205 M 12 F 17 F 30 M 158 F 3 2 2 2 2 2 2 3 3 2 2 2 Naples, Italy Nashville, TN Nashville, TN New York, NY 40.833 36.166 36.166 40.714 14.250 286.784 286.784 274.008 0 151 151 2 18.8 15.5 15.5 13.3 44.4 42.2 42.2 44.4 2F 2 (1,1) 2 (1,1) 6 (2,4) 55 F 20 (11,9) 17 (11,6) 97 (31,64) 3 1 2 2 Odense, Denmark Odense, Denmark Oxford, England Oxford, England 55.400 55.400 51.754 51.754 10.383 10.383 21.254 21.254 10 10 66 66 8.9 8.9 10.5 10.5 33.9 33.9 33.3 33.3 2 (1,1) 3F 3 (1,2) 5M 59 (38,21) 80 F 268 (78,190) 68 M 2 3 1 2 Cambridge, MA Charana, Bolivia Chicago, IL Clermont-Ferrand, France Clermont-Ferrand, France College Park, MD Columbia, MO Copenhagen, Denmark Maastricht, Netherlands Manta, Benin Matlab, Bangladesh Maywood, IL Melbourne, Australia Mexico City, Mexico Minneapolis, MN, US Minneapolis, MN, US Modena, Italy Mono Province, Benin Montreal, Canada Naples, Italy American Journal of Human Biology 529 CLIMATE AND BMR IN HUMANS TABLE B1. (Continued) Locality Latitude Longitude Elevation TMEAN HHIT Nu (M,F) Paine, Chile Palo Alto, CA 233.187 270.750 37.442 2122.142 368 29 14.9 15.8 36.7 41.7 2 (1,1) 4F Phala, Tibet Phala, Tibet Phala, Tibet Philadelphia, PA Philadelphia, PA Phoenix, AZ 30.500 N/A 30.500 N/A 30.500 N/A 39.952 275.164 39.952 275.164 33.448 2112.073 5150 5150 5150 8 8 343 3.4 3.4 3.4 13.3 13.3 24.0 38.9 38.9 38.9 48.3 48.3 47.8 2 (1,1) 3 (2,1) 2 (1,1) 2 (1,1) 1M 5 (2,3) 16 (7,9) 18 (12,6) 5 (1,4) 59 (31,28) 13 M 357 (128,229) 1 2 3 2 3 2 Pollgus and vicinity, Russia Pollgus and vicinity, Russia 61.842 61.842 95.550 95.550 213 213 21.0 21.0 33.9 33.9 1F 9 (5,4) 2F 127 (62,65) 1 2 Port Moresby, PNG Porto Alegre, Brazil Providence, RI Pune City, India 29.483 230.033 41.824 18.533 147.183 251.200 271.413 73.867 19 34 3 570 26.7 20.1 10.9 24.7 45.6 49.4 41.1 55.0 2 (1,1) 1F 1F 4 (2,2) 17 (9,8) 60 F 10 F 98 (44,64) 2 2 2 2 Quebec City, Canada Quebec City, Canada Rio de Janeiro, Brazil Rochester, MN Rochester, NY 46.800 46.800 222.900 44.022 43.155 271.250 271.250 243.233 292.470 277.618 71 71 1 322 155 6.2 6.2 24.2 8.4 9.4 37.8 37.8 41.7 44.4 41.1 2 (1,1) 2 (1,1) 1F 2 (1,1) 3 (1,2) 359 (154,205) 319 (146,173) 50 F 253 (100,153) 59 (26,33) 2 3 2 2 2 41.900 12.483 41.900 12.483 32.715 2117.156 32.715 2117.156 14 14 26 26 15.9 15.9 17.7 17.7 40.0 40.0 40.0 40.0 3 (2,1) 2 (1,1) 2M 4 (3,1) 68 (46,22) 108 (56,52) 14 M 47 (37,10) 2 3 2 3 37.775 2122.418 223.533 248.617 37.567 127.000 1.293 103.856 20.150 298.917 46.783 271.300 40.793 277.860 25.017 121.450 30.438 284.281 25.950 143.000 63.137 2142.524 35.700 139.767 60 637 34 1 2335 73 359 6 54 1634 547 20 14.6 20.6 13.2 28.2 14.7 8.2 10.7 23.2 19.9 18.5 22.7 16.7 37.8 45.6 43.9 46.1 42.8 37.8 44.4 50.0 42.8 24.0 28.9 42.8 1F 4 (2,2) 2M 1M 1F 1M 1M 2 (1,1) 1F 2 (1,1) 1M 2 (1,1) 17 F 58 (30,28) 96 M 20 M 12 F 24 M 12 M 223 (102,121) 10 F 16 (9,7) 8M 30 (15,15) 2 1 2 1 2 2 3 2 2 2 2 2 113 F 58 (30,28) 11 M 15 M 52 F 58 M 130 (62,68) 24 F 125 (12,113) 3 2 2 2 2 2 1 2 2 Rome, Italy Rome, Italy San Diego, CA San Diego, CA San Francisco, CA Sao Peulo, Brazil Seoul, South Korea Singapore Solis, Mexico Ste.-Foy, Canada State College, PA Taipei, Taiwan Tallahassee, FL Tari Basin, PNG Tetlin, AK Tokyo, Japan Tokyo, Japan Toronto, Canada Trenton, NJ Tsukuba Ibarakl, Japan Ubon, Thailand Vellore, India Verona, Italy Verona, Italy Wageningen, Netherlands 35.700 43.667 40.217 36.200 15.233 12.933 45.450 45.450 51.967 139.767 279.417 274.743 140.100 104.863 79.133 11.000 11.000 5.667 20 119 11 87 121 205 95 95 14 16.7 8.9 13.7 14.3 27.7 29.0 13.6 13.6 10.1 42.8 44.4 44.4 42.2 52.2 53.3 46.9 48.9 37.8 1F 2 (1,1) 1M 2M 1F 1M 4 (2,2) 1F 4 (1,3) Wageningen, Netherlands Wainwright, AK Zeist, The Netherlands 51.967 5.667 70.637 2160.038 52.100 5.233 14 7 5 10.1 210.8 10.5 37.8 25.0 36.1 1F 1M 2M Nw (M,F) 16 (8,8) 72 F 28 F 6M 24 M Age class 3 3 3 2 2 Reference(s) Aleman-Mateo et al., 2006 Taaffe et al., 1995; Thompson et al., 1997 Beall et al., 1996 Beall et al., 1996 Beall et al., 1996 Owen et al., 1986; Owen et al., 1987 Owen et al., 1987 Ferraro et al., 1992; Christin et al., 1993; Tataranni et al., 1994 Katzmarzyk et al., 1994 Katzmarzyk et al., 1994; Galloway et al., 2000 Yamauchi and Ohtsuka, 2002 Wahrlich and Anjos, 2001 Cullinen and Caldwell, 1998 Chiplonkar et al., 1992; Kanade et al., 2001 Loos et al., 2006 Loos et al., 2006 Magalhaes et al., 1999 Nielsen et al., 2000 Welle and Nair, 1990; Welle et al., 1992 Censi et al., 1998; Polito et al., 2000 Meunier et al., 2005 Nichols et al., 1990 Nichols et al., 1990; Morales et al., 1998 Bronstein et al., 1996 Hoffman et al., 2000 Kim et al., 2001 Stensel et al., 2001 Sanchez-Castillo et al., 2002 Deriaz et al., 1992 Williamson and Kirwan, 1997 Liu et al., 1995 Moffatt and Owens, 1991 Yamauchi and Ohtsuka, 2002 Milan et al., 1962 Yamauchi et al., 2004; Shinagawa et al., 2005 Ozeki et al., 2000 Buccholz et al., 2001 Schmidt et al., 1996 Doi et al., 2001 Lawrence et al., 1992 McNeill et al., 1987 Maffeis et al., 1993 Armellini et al., 2000 van Raaij et al., 1989; Weststrate et al., 1990; Voorrips et al., 1993; Spaaij et al., 1994 Voorrips et al., 1993 Milan and Evonuk, 1967 Velthuis-te Wierik et al., 1995 *Age class: 1, <18 years; 2, 18–50 years; 3, >50 years. 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