Editorial
Expanding Evidence for the Multiple Dangers of Epidemic
Abdominal Obesity
Adrian J. Cameron, MPH; Paul Z. Zimmet, MD, PhD, FRACP, FRCP
T
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he waistline of America has been expanding now for
decades,1 largely as a consequence of an obesogenic
environment, with a car-worshipping culture and take-away
lifestyle par excellence.2 No upper limit to the prevalence or
extent of obesity is yet apparent, and many countries and
communities worldwide are busily following the American
lead. Accumulating research evidence suggests that the personal and economic costs of the obesity epidemic are immense,3 driven by the obesity-related increases in risk for
conditions such as type 2 diabetes mellitus, the metabolic
syndrome, cardiovascular disease (CVD), kidney disease,
arthritis, cancer, asthma, and sleep-disordered breathing. In
addition, decreases are apparent in self-esteem and quality of
life.
related premature mortality because of the changing associations between obesity and mortality with age.13,14
In the present paper, the authors have demonstrated among
US women nurses a clear step-wise increase in risk for each
of cancer, CVD, and overall mortality with increasing quintiles of waist circumference or waist:hip ratio. The J-shaped
curve commonly seen in appropriately adjusted studies of
BMI and mortality (which results largely from increased
respiratory disease death among underweight individuals and
increased CVD and cancer death among the overweight and
obese) was not seen in this study. This demonstrates the
difference in outcomes from overall obesity as compared with
abdominal adiposity. Even though the results presented here
suggest a roughly linear association between waist circumference and mortality, it needs to be acknowledged that a
limit exists to the recommendation that a reduced waist
circumference decreases mortality risk. Diseases such as
anorexia and bulimia in more affluent societies, and the
chronic malnutrition still present in much of the developing
world, remind us that in another context, “underweight” can
and does also present an increased mortality risk.
The important debate as to which measure of obesity, waist
circumference, waist:hip ratio, or BMI, is “better” is probably
best divided into clinical and research perspectives. In the
busy clinical setting, the importance of this question relates to
whether the time-consuming burden of multiple measures of
obesity is indeed justified. Various practical and scientific
considerations are relevant here. First, the simplicity of the
message delivered by measurement of waist circumference to
the individual or patient is of paramount importance. For
example, who is unable to relate to the experience of a pair of
jeans that is feeling a little tight, or the belt that no longer
quite fits? Both BMI and waist:hip ratio are abstract concepts
in comparison. Second, and just as important, abdominal
obesity is a stronger predictor of obesity-related outcomes, as
demonstrated once again here by Zhang et al. Third, and the
only practical drawback to waist circumference, it is not easy
to obtain an accurate waist measurement, with no standardized protocol practiced, and different studies use different
locations to take the measurement.15 Even with a standard
protocol, clinicians will differ in the measurement of an
individual’s waist. Having said this, it is also true that
obtaining an accurate weight measurement is also surprisingly difficult because of inaccuracies in scales used, changes
with time of day, and variation in the amount of clothing
removed before measurement. Height measurement is also
not always entirely accurate. Finally the question arises of
whether the measurement of waist in addition to BMI helps to
identify an additional subset of the population at increased
risk. The findings from Zhang et al clearly demonstrate that
Article p 1658
Numerous very large cohort studies have also firmly
established obesity as being a strong and robust predictor of
both overall and CVD mortality in men and women.4 – 8 In
most of the studies reported to date, waist circumference was
not measured, with obesity measured using the body mass
index (BMI), a crude measure of overall obesity that, as
multiple studies have now shown, is often not the best
predictor of obesity-related outcomes.9 –11 In the current issue
of Circulation, Zhang et al expand on the already considerable evidence suggestive of a strong positive relationship
between overall obesity (using BMI) and mortality with a
report from the large Nurses’ Health Study examining the
impact of abdominal obesity (using waist circumference) on
all-cause, cancer, and CVD mortality in US women.12 The
study is well powered to examine such associations, with over
3500 deaths during the 16 years of follow-up. As noted by the
authors, this is one of only a handful of studies to examine the
association of waist circumference and mortality, with most
of the others also showing strong associations. Two studies
failed to show an association between waist circumference
and mortality, but these were conducted in much older
populations that, although they may have substantial mortality, were less likely to present the full picture of obesityThe opinions expressed in this article are not necessarily those of the
editors or of the American Heart Association.
From the International Diabetes Institute and Baker Heart Research
Institute, Melbourne, Australia.
Correspondence to Paul Zimmet, AO, MD, PhD, FRACP, FRCP,
FTSE, Director International Diabetes Institute, 250 Kooyong Rd,
Caulfield VIC 3162, Australia. E-mail [email protected]
(Circulation. 2008;117:1624-1626.)
© 2008 American Heart Association, Inc.
Circulation is available at http://circ.ahajournals.org
DOI: 10.1161/CIRCULATIONAHA.108.775080
1624
Cameron and Zimmet
Multiple Dangers of Epidemic Abdominal Obesity
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among those women classified as “normal” after measurement of BMI, the risk of mortality (and CVD mortality in
particular) increases if they are also classified as obese by
waist circumference. The same is true among those classified
as normal by waist circumference but obese by BMI. This
would appear to suggest that in women both BMI and waist
circumference provide important components of mortality
risk.
Does this mean that measurement of both central and
overall adiposity in the clinical setting is justified? On the
surface, it would appear so. However, to answer this question
fully requires both an analysis of whether models that include
both waist circumference and BMI are significantly better
than those that contain waist circumference alone (for example, comparing the area under the receiver operating characteristic curve for both models) as well as an examination of
the implications in a population setting. The correlation
between continuous BMI and waist variables in the Nurses’
Health Study was high, reported as 0.81 by Zhang et al. Yet,
the concordance of waist and BMI in categorizing the
population into normal, overweight, and obese using established cut points is not nearly so high. In the national
Australian Diabetes, Obesity and Lifestyle (AusDiab)
study,16 95% of women who were classified as obese by BMI
were also classified as obese by waist circumference, but
conversely, only 58% of those deemed obese by waist
circumference were also obese by BMI. Similarly, 85% of
those classed as overweight by BMI are either overweight or
obese by waist circumference, but only 63% of those overweight by waist are classified similarly or worse by BMI. The
upshot of this is that even though BMI and waist are largely
colinear,17 someone classified as overweight, or even more
particularly obese, by BMI is overwhelmingly likely to be
similarly classified by waist circumference, but not vice
versa. The main reason for this is that using the cut points
suggested for Europids, obesity defined using waist circumference identifies a much larger proportion of the population
than does obesity defined by BMI. So, even though the
mortality risk may be higher in those identified as obese by
both waist and BMI, in reality, measuring BMI in addition to
waist will not identify a large additional population at higher
risk (at least using currently recommended cut points18),
whereas using waist circumference alone will identify both
those already identified by BMI as obese, plus a significant
additional high-risk population.
Summarizing all of these arguments leads to the conclusion
that monitoring changes in waist size (whether or not the cut
points are taken into consideration) is as important, or even
more important, than monitoring changes in weight and BMI.
The findings of Zhang et al confirm the importance of this, at
least for women (analysis of similar male cohorts is therefore
also required to confirm these findings for both sexes). The
simple measurement of waist circumference should be
strongly encouraged in the clinical setting and also as a health
promotion message to encourage prevention of the multiple
obesity-related outcomes such as type 2 diabetes mellitus,
CVD, and also death.
An interesting and controversial facet of the relationship
between obesity and mortality that was not addressed in the
1625
report of Zhang et al is the changes in this relationship that
occur with age. Obesity has different implications not only
based on the degree of severity, but also on the age at which
it develops. This is a reality and an issue that is seldom
addressed, usually because of the absence of lifetime data or
numbers of subjects and events that are inadequate for
analyzing mortality by age group. Stevens et al addressed this
question in their analysis of the relationship between age,
BMI, and mortality in the large American Cancer Prevention
Study, demonstrating that the strength of the relationship
between mortality and BMI declined with age (even though it
remained significant up to age 74 years).8 This conclusion
could explain the absence of an association between waist
circumference and mortality seen in those 2 studies that only
included elderly subjects13,14 and suggests that, whereas
obesity needs to be recognized as an important risk factor for
mortality (and other outcomes), the message of its health
implications needs to be particularly directed at younger
populations. The heightened risk of obesity in younger
populations is 2-fold: firstly, they have a lifetime in which the
consequences of their obesity can be played out, and secondly, they have a longer time in which their adiposity can
further increase. For these reasons, a push to curb childhood
and adolescent obesity is of paramount importance.
A final mention of the novel findings on the strong
relationship between central obesity and cancer mortality in
the present study should be made. These results are of great
importance and serve to further highlight the multifaceted
nature of the consequences of an obesity epidemic. The
multiple important messages on the consequences of obesity
presented in this paper come at an opportune time, with little
evidence to date of the paradigm shift in thinking required to
prevent a worsening of the obesity-related crisis and to attack
the environmental and behavioral issues that are creating the
obesogenic environment that surrounds us.
Disclosures
None.
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KEY WORDS: Editorials 䡵 mortality 䡵 obesity
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Expanding Evidence for the Multiple Dangers of Epidemic Abdominal Obesity
Adrian J. Cameron and Paul Z. Zimmet
Circulation. 2008;117:1624-1626
doi: 10.1161/CIRCULATIONAHA.108.775080
Downloaded from http://circ.ahajournals.org/ by guest on June 17, 2017
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