Milk Consumption, Calcium Intake, and
Decreased Hypertension in Puerto Rico
Puerto Rico Heart Health Program Study
M A R I O R. GARCIA-PALMIERI, M.D.,
MERCEDES C R U Z - V I D A L , M.D.,
RAUL COSTAS, J R . ,
PAUL D. SORLIE, M.S.,
AND RICHARD J. HAVLIK,
M.D.,
JEANNE TILLOTSON,
M.A.,
M.D.
Downloaded from http://hyper.ahajournals.org/ by guest on June 17, 2017
SUMMARY The baseline observations in the Puerto Rico Heart Health Program during 1965-1968
involved blood pressure determinations, other measurements, and a 24-hour dietary recall in 7932
men aged 45-64 years. This extensive data base provided an opportunity to test the hypothesis that low
calcium intake is related to increased blood pressure level. Among men without baseline coronary
heart disease and not taking antihypertensive medication, there was an inverse relationship between
milk consumption and definite hypertension in urban Puerto Rican men and older rural men. When
data from all age and area groups had been averaged, a twofold increase in hypertension was found in
subgroups who drank no milk compared to those who consumed over 1 quart of milk a day. Similar
trends were found when an estimate of total calcium intake from food, principally from milk, was
used. With multivariate analysis while known correlates of blood pressure were simultaneously
considered, an independent effect persisted between milk consumption and blood pressure. These
results appeared to confirm an inverse association between calcium and hypertension. It was still not
possible to ascribe a causal relationship between calcium and blood pressure, however, due to the
intricate network of covarying food intakes, the factors related to absorption or lack of absorption of
calcium, and the possible role that unmeasured social and cultural factors may play in the observed
relations. (Hypertension 6: 322-328, 1984)
KEY WORDS
• epidemiology
• nutrition
• blood pressure
R
cohort of 8000 Japanese-American men in Hawaii,
milk intake was inversely associated with high systolic
and diastolic blood pressure.4 Analysis of dietary calcium intake and blood pressure in the first National
Health and Nutrition Examination Survey5 revealed a
significant inverse correlation, but this correlation was
of a low order of magnitude. A separate investigation6
of the same data set found no relationship between
blood pressure and intake of dairy food, and a positive
relationship between total serum calcium and high
blood pressure. Another inconsistent report in Belgium Army personnel involved a positive relationship
between 24-hour urinary calcium, total serum calcium, and blood pressure.7 In a clinically ill patient, a
relationship has been reported8 between hypercalcemia
and hypertension, with reversibility of hypertension on
lowering of calcium. Because of the availability of
extensive dietary and cardiovascular information on a
large population of urban and rural Puerto Rican men,
it was possible to test the reported hypothesis that dairy
products or dietary calcium potentially may have a
relationship to hypertension.
ECENT reports have suggested that hypertensive individuals consume less calcium in their
diets, especially in the form of cheese, and
have lower ionized serum calcium levels when compared to control subjects.1-2 Consistent with such findings is the observation that certain countries with diets
traditionally high in calcium have a low incidence of
hypertension with pregnancy. 3 In addition, among a
From the Department of Medicine, University of Puerto Rico
Medical School, San Juan, Puerto Rico (Garcia-Palmieri, Costas,
and Cruz-Vidal); and the Division of Heart and Vascular Diseases,
National Heart, Lung, and Blood Institute, Bethesda, Maryland
(Sorlie, Tillotson, and Havlik).
Supported in part by Contracts PH43-63-620 and NO 1 HV 42902
from the National Heart, Lung, and Blood Institute, National Institutes of Health, U.S. Public Health Service, to the University of
Puerto Rico.
Address for reprints: Dr. Mario R. Garcia-Palmieri, Director,
Programa de Salud del Corazon, c/o Department of Medicine, University of Puerto Rico, School of Medicine, G.P.O. Box 5067, San
Juan, Puerto Rico 00936.
Received February 16, 1983; revision accepted September 28.
1983.
322
MILK CONSUMPTION AND BLOOD PRESSURE/Garcia-Palmieri et al.
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Methods
Population and Baseline Characteristics
The Puerto Rico Heart Health Program9 examined
men from four rural and three urban areas during the
years 1965-1968. Rural areas were defined as enumeration districts containing fewer than 25 dwelling
units in a cluster, and urban areas as enumeration districts with 25 or more dwelling units in a cluster. A
house-to-house census of these enumeration districts
was made by the personnel who regularly conducted
the decennial census. All men between 45 and 64 years
of age were invited to participate in the study, and their
ages were verified at the time of the initial visit. The
response rate was 79.9% in the urban and 82.4% in the
rural areas, so that the proportion of urban/rural population in the study was approximately the same as in
the general population. No other method of selection
was used. Thus, the study population consisted of men
aged 45 to 64 years at baseline who were initially free
of coronary heart disease and not taking any antihypertensive medication. The first blood pressure measurements were made by a physician with the patient seated; diastolic pressure was designated by the Phase V
Korotkoff sound. Normal blood pressure was defined
as a systolic level lower than 140 mm Hg and a diastolic level lower than 90 mm Hg. Hypertension was defined as a systolic blood pressure over 160 mm Hg and
a diastolic pressure over 95 mm Hg. All other combinations of values were considered borderline. After
requiring subjects to successfully complete a 24-hour
diet recall, the study had a final population of 7932
men, 30% of whom were from the rural area. Relative
weight was determined as a ratio of the observed
weight at baseline to a standard weight for height from
the Metropolitan Life Insurance tables.10 Education
level was determined by highest grade completed in
school and analyzed by grouping into six categories.
Standard methodology for the 24-hour recall was
utilized. Most interviews were done during one of the
regular 5 work days, so that most diet information
referred to Sundays through Thursdays. However,
some interviews were performed on Saturdays, so
there was information on Friday diets as well. No
interviews were done on Sundays. In all cases, the day
of the week for which the data were taken was identified as Monday-through-Thursday, Friday, Sunday, or
holiday." 1 2 It was necessary to devise a relatively
simple system for dietary data collection and computation that could be administered equally to rural and
urban men of varying degrees of sophistication and
that also could be processed easily using local resources. For this reason, most "basic" foods (milk,
cheese, eggs, meat, and so forth) reported eaten during
the 24-hour recall interview were tallied for entry into
the computer in terms of standard portions; nutrient
intake from these items was determined by computation using a nutrient data base appropriate to the area.
Mixed dishes (involving recipe calculation) and less
frequently eaten basic foods were hand-calculated by
the dietitian-interviewers, and nutrients consumed
323
from these sources were entered into the system in
order to obtain each subject's total 24-hour nutrient
intake. Subjects on special diets were not excluded
from analysis.
Because of the current interest in calcium-containing foods, the original food composition table was
supplemented for this investigation by the addition of
dietary calcium values based on standard American
and Latin American reference sources. 1314 This allowed an estimate of daily calcium intake to be made
for each study participant. While it was possible to add
calcium figures for the basic commonly eaten foods to
the original nutrient data base retrospectively, it was
not possible to estimate dietary calcium intake from the
recipe items eaten. Although approximately 40% of
the diet recalls included foods from recipe sources, the
amount of extra food from the sources was small. On
the average, only 10% of the total kilocalories consumed were from recipe foods. Thus, for this report,
calcium intake from these foods was omitted.
Statistical Methods
Stratification by age and area of residence was maintained during analysis. Relationships between blood
pressure and baseline characteristics were estimated by
product moment correlation coefficients and multiple
linear regression analysis. The statistical analysis system (SAS) was used to calculate these statistics.
Results
The average daily intake of milk for both urban and
rural subjects was about 16 oz per day (Table 1). Milk
was most frequently taken with coffee (a usual proportion would be 1 oz of Puerto Rican coffee to 2 oz of
evaporated milk, equivalent to 4 oz of whole milk).
Relatively small intakes of other dairy products such as
TABLE I. Prevalence Rates ojHypertension by Quantity o]Milk
Consumed by Puerto Rican Men
Urban men
Rural men
Milk consumption:
24-hour recall
None
4 or 8 oz
45-54
yrs
Rate
(%)
7.1
55-64
yrs
Rate
(%)
45-54
yrs
Rate
(%)
55-64
yrs
Rate
(%)
12.7
19.7
26.5
9.0
13.2
15.0
20.3
12 or 16 oz
6.1
11.4
10.8
17.3
20 or 24 oz
5.3
9.0
10.8
13.5
28 or 32 oz
6.0
11.3
7.8
15.8
>32oz
8.8
9.5
4.4
13.4
Population number
Average consumption
(oz/day)
1222
16.0
1144
16.6
3330
15.9
2236
16.0
Data from Examination 1, Puerto Rico Heart Health Program, of
men free of coronary heart disease and not taking antihypertensive
medication. Milk consumption was recorded in 4 oz units/day.
324
HYPERTENSION
TABLE 2. Correlation Coefficients between Milk Consumption
and Other Specified Characteristics for a Population Free ofCHD,
Not on Antihypertensive Medications, and with Known Values of
All Measurements at Examination 1; The Puerto Rico Heart Health
Program
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Rural men
45-54 55-64
Characteristics
yrs
yrs
-0.05
-0.06
Systolic BP (mm Hg)
Diastolic BP (mm Hg)
-0.02
-0.07
0.39
0.46
Protein (g)
0.36
0.40
Fats (g)
0.31
Carbohydrates (g)
0.33
0.14
0.15
Coffee (g)
-0.11
-0.07
Alcohol (g)
0.13
Education (levels)
0.11
Blood glucose (mg/dl)
0.02
0.07
Relative weight (%)
0.01
0.03
Heart rate (bpm)
0.00 -0.04
Cigarettes smoked (no./day)
0.05
0.02
0.02
0.04
Age (yrs)
Population number
1209
1133
Urban
45-54
yrs
-0.12
-0.12
0.37
0.29
0.27
0.23
-0.14
0.04
0.02
-0.08
-0.03
0.05
0.02
3312
men
55-64
yrs
-0.08
-0.07
0.41
0.36
0.29
0.22
-0.14
0.02
0.03
0.01
-0.01
0.02
0.02
2225
Minimum correlation
statistically significant
at p < 0.05
±0.06 ±0.06
±0.04 ±0.05
Data from Examination 1, Puerto Rico Heart Health Program, of
men free of coronary heart disease and not taking antihypertensive
medication. Milk consumption was recorded in 4 oz units/day.
cheese and ice cream were reported, with the lowest
intakes reported by rural men. The average calcium
intake from whole or evaporated milk was 587 mg for
rural and 573 mg for urban men, with the next largest
nondairy calcium source being legumes.
VOL 6, No 3, MAY-JUNE
Individuals who consumed more milk had a lower
prevalence of hypertension than those who consumed
less milk. This relationship was observed in all area
and age groups except in the younger rural group (Table 1). The relationship was strongest in urban men
aged 45 to 54 years, where 20% of those who consumed no milk were hypertensive and only 4% of those
who consumed more than four glasses a day were
hypertensive.
The relationship between milk consumption and
systolic blood pressure can be expressed as a correlation coefficient (Table 2). The magnitude of this correlation ranged from —0.05 to —0.12, depending on
age and geographic area. Correlations with diastolic
blood pressure were similar. Milk consumption was
highly correlated with total protein, fats, and carbohydrates, largely because milk contributed to the overall
levels of these nutrients. Milk consumption was also
positively correlated with coffee drinking since coffee
was usually drunk with milk, and inversely correlated
with alcohol use. There was a small positive association of milk use with higher education and the greater
number of cigarettes smoked. Correlations between
systolic blood pressure and these variables were generally weak except for the known associations of blood
glucose, relative weight, and heart rate.
To correct simultaneously for interrelationships
among milk, other variables, and blood pressure, multivariate regression analysis was used (Table 3). A
significant inverse relationship between milk consumption and systolic blood pressure persisted in three
of the four subgroups. By using the unstandardized
regression coefficients, it was possible, for example,
to estimate that an increment of 16 oz of milk would
theoretically be equivalent to a 2 mm Hg decrease in
systolic blood pressure.
The results of the multiple linear regression model in
Table 3 show the inability of measured characteristics
TABLE 3. Multivariate Regression Coefficients of Systolic Blood Pressure (mm Hg) on Specific Variables
Variable
Milk consumption (4 oz units/day)
Protein (g)
Fats (g)
Carbohydrates (g)
Coffee (g)
Alcohol (g)
Education (levels)
Blood glucose (mg/dl)
Relative weight (%)
Heart rate (bpm)
Cigarettes smoked (no./day)
Age (yrs)
(R2)
*p < 0.05.
tp < 0.01.
Rural men
55-64 yrs
-0.522*
0.012
0.019
-0.009
-0.581
0.028
0.200
0.087t
0.310t
O.387t
-0.066
0.704t
(0.136)
45-54 yrs
-0.350
0.015
-0.019
-0.002
-0.311
0.018
0.003
0.096t
0.282t
0.314t
-0.005
0.5321
(0.157)
1984
Urban men
55-64 yrs
45-54 yrs
-0.557t
-0.414*
0.025
-0.032
-0.011
-0.001
-0.004
-0.001
-0.405*
-0.012
0.034t
-0.191
0.025*
0.25 I t
0.282t
-0.047
0.043t
1.108t
-0.001
0.215t
O.35Ot
-0.115t
0.764t
0.790t
(0.129)
(0.115)
MILK CONSUMPTION AND BLOOD PRESSUREJGarcia-Palmieri et al.
TABLE 4. Comparison of Standardized Multiple Regression Coefficients of Milk in Models Containing Systolic and Diastolic Blood
Pressure Measurements
Rural men
Urban men
Ace
group Regression Std coeff
Std coeff
of milkt
model*
of milkt
t
t
(yrs)
45-54
SBP
-0.0200 -1.66
-0.0298 - 4 .31
DBP
-0.0038 -0.31
-0.0252 - 4 .08
55-64
SBP
-0.0247
-2.05
-0.0188 - 2 .18
DBP
-0.0200 -1.66
-0.0163 - 1 .88
•SBP model: systolic blood pressure (dependent variable); milk,
protein, fats, carbohydrates, coffee, alcohol, education, blood glucose, relative weight, heart rates, cigarettes smoked, age (independent variables). DBP model: diastolic blood pressure (dependent variable); same independent variables as above.
^Coefficient of milk standardized by dividing by standard deviation of SBP or DBP.
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to adequately describe the variation in blood pressure.
The percentage of variation of blood pressure described by this model (R-squared) was between 11.5%
and 15.7% depending on age and geographic area. The
variable, milk consumption, although statistically significant, contributed only slightly to the explanation
since removal of the milk variable reduced the Rsquared by a difference of 0.5% at most. In multiple
regression, there is a possibility that highly correlated
variables may confuse the interpretation of individual
coefficients. In this analysis, the variables of protein,
fats, and carbohydrates were highly correlated with
each other, but when they were dropped from the model, there was little change in the coefficient for milk.
The variables of protein, fats, and carbohydrates had a
low correlation with blood pressure.
325
The results of the regression analysis were nearly the
same when diastolic blood pressure was used in the
model. The results are compared in Table 4 where the
regression coefficient for milk has been standardized
so that its magnitude is roughly comparable in the
models with systolic and diastolic blood pressure. The
magnitude of the effect of milk on diastolic blood pressure was slightly less than on systolic blood pressure,
and in the older age group it did not reach statistical
significance.
The possible effect of coffee use as a confounder
was more carefully investigated. The relationship between coffee and milk consumption, as measured by a
correlation coefficient of about 0.2, could have been an
important confounding factor since coffee has an inverse relationship with blood pressure (Table 3). There
was, however, a considerable range of milk use at each
level of coffee consumption. The prevalence rates of
hypertension by increasing milk use were stratified by
coffee consumption (Table 5). When we controlled for
coffee consumption by stratifying according to ounces
of coffee consumed, we found a decreasing prevalence
of hypertension with increasing milk use. Thus, the
results are consistent with those from the multivariate
analysis. A similar analysis stratifying by alcohol consumption showed an inverse association between systolic blood pressure and milk in both drinkers and
teetotalers (Table 5).
To investigate a possible confounding or interactive
effect of weight, prevalence rates of hypertension by
milk levels were calculated in the leaner group (relative weight less than 110) and in the heavier group
(greater than 110). A relative weight index of 100
means a weight equivalent to the ideal weight stan-
TABLE 5. Age-Adjusted Prevalence of Hypertension by Milk Consumption and Alcohol Use, Coffee Use, and Relative
Weight
Milk consumption
None
4 or 8 oz
12 or 16 oz
20 or 24 oz
28 or more oz
Total
No. with known values
Alcohol use
No
Yes
Coffee use
0-3 oz
4+ oz
8.3
9.6
9.9
12.7
8.6
10.8
Rural men
8.2
12.3
10.1
11.5
5.0
11.2
8.0
6.0
8.7
8.7
8.6
10.6
10.0
10.0
11.3
7.7
6.9
1883
483
1456
7.4
909
Relative weight (%)
2SI10
<110
10.1
9.0
7.9
5.1
18.7
16.4
11 1
17.2
6.2
15.4
5.2
5.3
1625
740
Urban i•nen
None
4 or 8 oz
12 or 16 oz
20 or 24 oz
28 or more oz.
22.9
16.7
12.9
12.0
10.0
22.0
19.8
18.7
13.1
13.6
23.9
18.6
14.9
12.1
11.4
19.9
12.3
11.6
12.2
Total
13.6
17.8
15.7
No. with known values
4127
1439
4099
9.4
19 4
11.9
10.0
6.1
8.0
25.6
20.9
16.5
16.1
12.3
11.7
10.0
17.5
1463
2060
3502
HYPERTENSION
326
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dards published by the Metropolitan Life Insurance
Company10 in 1959. An inverse trend was seen in the
urban area for both relative weight groups, which was
also suggested in the leaner rural group (Table 5).
While milk contributes several unique factors to the
diet, such as lactose, tryptophan, and riboflavin, it is
also the main contributor of calcium. Milk provides
slightly more than 60% of all calcium intake, with peas
and beans contributing the next largest percentage
(around 10%). However, when the amount of calcium
of the specified food groups was correlated with systolic blood pressure, calcium from milk showed the
largest correlation.
An alternative method of displaying the results is to
present mean values of calcium intake by classes of
hypertensive, borderline, and normal. Figure 1 shows
that the mean intakes of calcium from nondairy sources
were nearly identical for all of the blood pressure
groups for each age and area. There was also little
difference in the mean values of calcium from dairy
sources other than milk, such as cheese and ice cream.
The mean value of calcium from milk was less in the
hypertensive individuals.
A further possible confounder in this analysis is that
the urban population was approximately 15% black.
The ethnic classification of black or white in this study
was based on skin color determination, and thus the
groups were subsequently described as dark- or lightskinned. In Puerto Rico, the dark-skinned population
has slightly higher blood pressure and generally a
greater degree of lactose intolerance. When our analysis of the urban area was stratified by skin color, the
correlation between blood pressure and milk consumption was stronger in dark-skinned than light-skinned
individuals (Table 6). Also, the multiple regression
VOL
6,
Milk consumption
None
4 or 8 oz
12 or 16 oz
20 or 24 oz
28 or 32 oz
>32oz
Total
No.
10.4
15.9
1787
1077
-0.12
-0.13
16.0
287
17.1
217
-0.07
-0.05
-0.18
-0.16
-0.14
-0.11
Multiple regression
Standardized coefficient
of milk in*
SBP model b
t
DBP model b
t
-0.033 -0.001
-3.55 -0.10
-0.030
0.006
0.49
-3.28
-0.057
-2.15
-0.048
-1.81
-0.039
-1.27
-0.038
-1.25
•Standardized by dividing by the standard deviation of SBP or
DBP.
NON DAIRY
H
1984
Correlation coefficients
Correlation of milk
with
SBP
DBP
600
I DAIRY-NOT MILK
MAY-JUNE
Dark skinned
Light sskinned
45-54 55-64
45-54
55-64
yrs
yrs
yrs
yrs
Hypertension prevalence (%)
25.0
27.8
18.0
27.1
21.6
25.9
13.9
18.0
9.4
14.6
12.9
10.3
14.4
8.6
6.1
8.8
8.8
9.5
14.3
14.9
16.7
0.0
3.1
12.4
800
I
3,
TABLE 6. Prevalence of Hypertension by Milk Consumption;
Correlation and Regression of Milk Consumption and Blood Pressure in Those with Light and Dark Skin, Urban Area Only
1,000
CALCIUM
FROM:
No
400
c
I
DAIRY-MILK
200
AGE IN YEARS
FIGURE 1. Mean value of calcium intake and two standard errors by
hypertension status (hypertension, borderline and normal). Data from
the Puerto Rico Heart Health Program population free of coronary heart
disease and not on antihypertensive medication.
MILK CONSUMPTION AND BLOOD PRESSVRE/Garcia-Palmieri et al.
coefficients for milk were larger in dark-skinned than
light-skinned Puerto Ricans. An inconsistent finding
in Table 6 is that the multiple regression coefficient in
urban light-skinned men aged 55 to 64 years was not
statistically significant, although for those aged 45 to
54 years it was strongly significant.
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Discussion
The average daily intake of milk of 16 oz per day
reported in our study is comparable to that reported by
Fernandez and coworkers" from an island wide nutrition survey carried out in 1966 on a representative
sample of the entire Puerto Rico population. In that
survey rural adults reported consuming an average of
1.8 cups of milk per day and urban intakes averaged
2.2 cups per day, usually with coffee.
Although Puerto Rico has a coronary heart disease
rate approximately half that of the U.S. mainland,
hypertension is prevalent and is the most important
predictor of subsequent cardiovascular disease.16
Thus, the identification of potential additional blood
pressure correlates has public health implications for
this population. The Puerto Rico Heart Health Program has collected an extensive data set on a large
group of middle-aged Puerto Rican men. Because of
the availability of these 24-hour diet recall data collected in a standardized manner, it was possible to explore, by other methodology, the conclusion in a casecontrol study report1 of an inverse relationship between
dietary calcium and hypertension.
The initial analysis of the data, using correlation
coefficients, suggested a modest inverse association of
milk consumption and blood pressure. From this investigation we cannot be certain if this weak association indicates a true relationship or merely a poorly
measured one. The latter situation is possible since it is
unlikely that a single 24-hour diet recall is adequate to
characterize an individual's usual intake of dairy products or calcium. Unfortunately, multiple 24-hour recall data on the same individual, which would give a
better estimate of usual intake, are not available in this
population.
Further analyses indicated that those drinking no
milk had twice the prevalence of hypertension as those
who drank a quart or more per day. An intensive search
for confounding variables among nutritional and nonnutritional factors was attempted, but with multivariate analysis the relationship persisted in three of four
age/area subgroups. Possible confounding with coffee
and alcohol was explored. The same inverse relationship persisted in separate groups of beverage drinkers
and nondrinkers.
Since the average cheese consumption in this study
was small, a satisfactory comparison with one of the
previously reported studies was not possible.1 However, there was not a major trend toward a lower frequency of hypertension with increasing calcium from nonmilk dairy sources (Figure 1). Most of the difference
appeared to be from calcium in milk. It was not sur-
327
prising that when the various sources of calcium were
combined and participants were classified by hypertensive status, a similar inverse trend was found in
three of the four groups. Generally, the borderline
hypertensive subjects had an intermediary calcium intake. No satisfactory explanation exists for the inconsistent findings in the young rural group.
An important issue that could be addressed somewhat in this particular population was the possibility
that a subgroup with significantly higher blood pressure and a potential lactase deficiency by virtue of
darker skin color might, because of the unpleasant side
effects of milk ingestion, avoid dairy products. Skin
color had previously been assessed in urban men in this
population.17 Although the milk/blood pressure relationship was slightly less consistent in the light- than in
the dark-skinned individuals, this explanation does not
account for the blood pressure/milk relationship. It is
not possible in Puerto Rico to identify subgroups exactly comparable to the designation on the mainland of
black or white.17
Since the mechanism for an association between
milk consumption per se or dietary calcium from milk
and blood pressure is uncertain, the relationship must
be investigated further in diverse populations as well as
in laboratory situations. It will be necessary to determine whether a covariable of milk that affects blood
pressure could be operating. There could be cultural or
social factors associated with milk drinking that have
an unmeasured impact on blood pressure. Other foods
consumed with milk products could be affecting absorption of calcium.18 It is also possible that a high
milk-containing diet might decrease absorption of
trace metals, such as cadmium and lead, which have
been implicated in the pathogenesis of hypertension.19
Some other substances in milk, such as tryptophan,20
lactose, riboflavin, or fortification with Vitamin D,
could also be important factors.
Although the chain of causation has been postulated
to involve decreased dietary calcium intake leading to
lower ionized serum calcium which in turn results in
higher blood pressure,2 the inconsistent findings from
Kesteloot and Geboers7 that increased total serum calcium and urinary calcium are related positively to
blood pressure needs resolution. The known hypotensive effects of calcium-channel blocking drugs must be
considered as well.
Even if a causal relationship is accepted, the public
health implications of the findings must be carefully
considered. Since this is a very large population, statistical significance does not directly translate into a practical program for individuals. For example, from the
multivariate regression coefficients in Table 3, which
relate milk intake to systolic blood pressure, one would
predict that drinking two glasses of milk (16 oz) per
day would be associated with a decrease in systolic
blood pressure of only about 2 mm Hg, as compared to
a nondrinker. Of course, even this modest relationship
is only theoretical and would require a clinical investigation to confirm. In the Puerto Rico population, the
estimated mean intake of calcium is already approxi-
HYPERTENSION
328
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mately 900 mg per day. This is a value well within the
range of the recommended daily dietary allowances for
calcium for adult men established by the Food and
Nutrition Board of the National Academy of Sciences
— National Research Council.21
In addition, while milk consumption is associated
with blood pressure in a beneficial way, milk also
contributes a large amount of saturated fatty acids to
the diet. In this study, the correlation between milk
consumption and total saturated fatty acids in the diet
was about 0.50. Dietary studies generally show low
but positive correlations between saturated fatty acid
intake and serum cholesterol. In the Puerto Rico study,
this translates into a small but consistently positive
correlation between milk consumption and serum cholesterol that is between 0.02 and 0.05 depending upon
age group and geographic area.
The possible implications for the development of
coronary heart disease must be considered. Of course,
skim milk or calcium supplementation might be an
alternative for increasing calcium intake while maintaining a low saturated fat intake. Before major dietary
changes can be recommended, further studies are necessary to clarify the etiological nature of the relationship as well as to define the risks and benefits of any
recommended changes.
Acknowledgment
The authors appreciate the encouragement of Dr. William Zukel
in pursuing the present analysis.
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M R Garcia-Palmieri, R Costas, Jr, M Cruz-Vidal, P D Sorlie, J Tillotson and R J Havlik
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Hypertension. 1984;6:322-328
doi: 10.1161/01.HYP.6.3.322
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