acculturated vegetarians vary widely with respect to diet, social environment, and lifestyle, eg, macrobiotic vegans live in communes and eschew dairy products.
Vegetarian or causal Lawrence
Barrie
diet and blood association?3
J Beilin,
MD;
M Margetts,
Ian
PhD;
L Rouse,
and Robert
PhD;
pressure Bruce
levels:
KArmszrong,
Vandongen,
MB
incidental BS,
DPhil
Oxon;
MD
blood
pressure-lowering
effect
ofa
lactoovovegetarian
diet
with
reversible
changes
of 5-6
mm
Hg systolic and 2-3 mm Hg diastolic occurring over 6-wk periods. Similar dietary effects in mild hypertensive subjects provides impetus for identifying the responsible nutrients. Am JClin
Nutr
KEY
WORDS
l988;48:806-10. Diet,
hypertension,
blood
The possibility that eating a vegetarian diet might be responsible for lowering blood pressure was first suggested in a study in 1926 (1) in which Donaldson asked vegetarian college students to eat meat and observed a blood pressure rise within 2 wk of their doing so. However, as with many other studies of diet and blood pressure, the experiment was uncontrolled and may have been confounded by the stress experienced by students encouraged to eat meat contrary to their beliefs. Subsequently reports describing lower blood pressures in acculturated vegetarians compared with meat-eating populations (2) have included populations as diverse as Benedictine and Trappist Monks, American macrobiotic vegans (3), Seventh-day Adventist vegetarians in the United States (4) and Australia (5-8), and vegetarians in Israel (9). It will be clear from even these reports that the term vegetarian embraces a wide variety ofeating habits, lifestyles, and social environments. All the groups referred to come from so-called acculturated backgrounds and differ in at least one important aspect other than social milieu from nomadic unacculturated vegetarians whose diets are often characterized by a very low intake ofsodium (10). Even acculturated vegetarians vary widely with respect to diet, social environment, and lifestyle, eg, macrobiotic vegans live in communes and eschew dairy products as well as meat, fish, and poultry; Seventh-day Adventists 806
Am
iC/in
Nuir
pressure,
vegetarian
are more aptly described as lactoovovegetanans (ie, consume dairy products but not meat, fish, or poultry) but also avoid alcohol, caffeine, and nicotine; whereas Israeli vegetarians show no such obligate restrictions but nevertheless tend to drink and smoke less, exercise more, and are less obese than their age-matched meat-eating controls (9). Given the now well-established blood pressureraising effect of obesity and alcohol consumption (11, 12) and the blood pressure-lowering effects ofregular exercise (1 3), as well as the more immediate effects of mental state on blood pressure, it is doubtful whether any of the earlier studies on vegetarians’ blood pressures provide conclusive evidence as to the effect of diet per se rather than effects ofother differences in lifestyle. One interesting exception to the reports oflower blood pressures in vegetarians was the study ofHarris et al (14) in which 3 159 children aged 6-16 y attending Seventhday Adventist schools in California showed blood pressures similar to 4681 children from other schools. The I From the University Department ofMedicine, University of Western Australia Medical School, Royal Perth Hospital, Perth, and the NHMRC Research Unit in Epidemiology and Preventive Medicine, University of Western Australia Queen Elizabeth II Medical Centre, Nedlands, Western Australia, Australia. 2 Supported by the National Health and Medical Research Council of Australia, the Australian Kidney Foundation, and the Royal Perth Hospital Research Foundation. 3 Reprints not available.
1988;48:806-lO.
Printed
in USA.
© 1988 American
Society
forClinical
Nutrition
Downloaded from ajcn.nutrition.org by guest on June 6, 2013
ABSTRACI’ Evidence that nutrients other than the major cations may influence blood pressure levels stems from studies ofacculturated vegetarians and from randomized controlled dietary trials. Earlier studies of vegetarians focused on religious groups and on vegans, making it difficult to know whether their lower blood pressures were due to diet per se or to other aspects oflifestyle. Seventh-day Adventist vegetarians showed significantly less hypertension and lower blood pressures compared with Mormon omnivores, effects which were independent ofdifferences in obesity and not due to altered sodium intake. Subsequently, controlled dietary intervention studies in healthy normotensive omnivores provided more direct evidence for a
VEGETARIAN
(a)
180
DIET
(b)
In
170
160 32’
150
a.,
-f,, 140
130
;
120
4’; 50J59
o-g
70-79
30-39 AGE
FIG 1 . Blood pressure omnivores. Data for men tarians; ---, Narrogin and number in each age ence 7.
40-49
50-59
60-69
-79
(YEARS)
(BP)by age in SDA vegetarians and Narrogim are shown in a, for women in b.-SDA vegeomnivores. Results are mean with SEM and diet group is shown. Adapted from refer-
authors suggested that the potential effects of diet or other aspects oflifestyle might not become evident until later life. Some indication of a specific vegetarian-vs-meat dietary effect came from a brief report by Anholm et al in 1975 (15)(abstract only) ofa comparison ofblood pressures in Seventh-day Adventists lactoovovegetarians vs Mormon omnivores; Anholm et al found lower blood pressures in the vegetarians with the differences increasing with age. However no specific details ofpossible confounding factors such as obesity or salt intake were given. Mormons and Seventh-day Adventists are in several ways excellent controls for one another in that both groups avoid alcohol, caffeine-containing beverages, tobacco, and other stimulants and are deeply religious, but their diets contrast markedly with respect to meat, fish, and poultry. As a result ofthis report and the observations of Armstrong et al (7) that West Australian Seventh-day Adventist vegetarians attending a conference had lower blood pressures and less of a blood pressure rise with age than did the local townsfolk (Fig 1), Rouse et al (8) undertook a detailed comparison of blood pressures and lifestyles of Seventh-day Adventists and Mormons in Perth (Table 1). The object ofthis study was to try and determine the relative importance ofdiet and other aspects oflifestyle in determining the cause of any blood pressure differences between the two groups. All the subjects screened completed a lifestyle questionnaire and had blood pressures measured under carefully standardized conditions. Comparisons were made between 98 Seventh-day Adventist (SDA) lactoovovegetarians (eating meat, fish, or poultry less than once a month)
PRESSURE
807
with 82 (SDA) omnivores and 1 1 3 Mormon omnivores, aged 25-44 y. The SDA vegetarians were significantly slimmer than the Mormon omnivores but mean blood pressure adjusted for age, height, and weight were significantly lower in the vegetarians than meat eaters ( 1 15.6/68.7 and 12 1.2/72.2 mm Hg, respectively, in males and 109. 1/66.7 and 1 14.9/72.6 mm Hg, respectively, in females). These differences were not related to past or current use of alcohol, tobacco, tea and coffee, physical activity, personality characteristics, or degree of religious observance. The entire frequency distribution ofblood pressures was shifted to the left in the SDA vegetarians (Fig 2) and the prevalence of mild hypertension ( 140 mmHg systolic or 90 mmHg diastolic) was 10 and 8.5% in the Mormon and SDA omnivores, respectively, compared with 1-2% in SDA vegetarians. Analysis ofdiet records showed that the vegetarians ate significantly more fiber, polyunsaturated fatty acids, magnesium and potassium, vitamin C, and vitamin E and significantly less total fat, saturated fatty acids, cholesterol, Vitamin B-l2 and iron compared with Mormon omnivores. The SDA omnivores had dietary patterns and blood pressures that were intermediate to those of the SDA vegetarians and Mormon omnivores. In a detailed follow-up study of 47 randomly selected pairs of Adventist vegetarians and Mormon omnivores matched for sex, age, and obesity, home blood pressure readings showed consistent blood pressure differences (Table 2) (16). Moreover mean 24-h urinary excretion of Na was similar in the two groups although the vegetarians excreted significantly more K. These results with urinary Na are in accord with those of Arkwright et al (11) and indicate that the blood pressure differences were unlikely to be due to dietary Na. Although these comparisons between Seventh-day Adventist vegetarians and Mormons provide support for a specific blood pressure-lowering effect of a vegetarian diet, cross-sectional population studies cannot prove cause-and-effect relationships, and it is possible that other unidentified factors were contributing to the blood pressure differences. However the issue was resolved beyond reasonable doubt by randomized controlled dietary intervention trials in Perth that involved introducing a vegetarian diet to groups of regular meat eaters. In the first ofthese trials 59 healthy volunteer Hospital employees were assigned to one ofthree dietary groups after matching for age, sex, and obesity (17). After an initial familiarization period the first group in the trial continued their normal meat diet for two consecutive 6-wk penods; the second group ate a vegetarian diet for 6 wk and then reverted to their normal diets for 6-wk and the third group ate these diets in the reverse order. The volunteers had their two main meals a day prepared in the hospital canteen for 5d/wk and for all other meals were given specific advice about a lactoovovegetarian diet typical of that eaten by the West Australian Seventh-day Adventists. Subjects were also encouraged to maintain other aspects of lifestyle constant for the duration of the study, including total calorie consumption, physical activity,
Downloaded from ajcn.nutrition.org by guest on June 6, 2013
::3j
AND BLOOD
808
BEILIN
TABLE 1 Twenty-four-hour
nutrient
intake
ofAdventist
vegetarians:
Adventist
ET AL
ommivores
and Mormon
omnivores
Men Adventist vegetarians Energy (MJ) (kcal) Totalcarbohydrate(g) Dietaryfibre(g)
Protein (g) Total fat (g) Saturated fatty acids(g) Polyunsaturatedfattyacids(g) P:S ratio Cholesterol(mg) Sodium(mmol) Potassium(mmol) Magnesium (mmol) 6
SD. From
t Significantly Significantly
reference different different
10.50 ± 2.71 2510±648 332±91 41.4± 17.5 92.7 ± 26.3 95.5 ± 33.3 37.2 ± 16.7 18.6± 11.5 0.57 ± 0.36f 272±2l7f 163±73 112±38 20.6 ± 8.1
Mormon ommivores
Adventist vegetarians
1 1.62 ± 4.29 2777±1025 321±116 24.3± l6.lt 103.6 ± 39. 1 126.9 ± 57.4 50.3 ± 25.3t 18.4± l4.2f 0.4 1 ± 0.36t 398±2llt 155±67 92±37t 15.5 ± 7.9t
8.55 ± 2.63 2040±629 261±87 32.6± 11.9 72. 1 ± 24.0 83.2 ± 34.8 29.2 ± 13.7 19.0± 12.7 0.77 ± 0.62 208±159 131±56 88±29 16.3 ± 5.5
Adventist ommivores
Mormon omnivores
8.00 ± 2.75 1910±657 240±88 27.1 ±8.9 66.9 ± 24.4 79.9 ± 35.6 31.3 ± 16.5 l3.7±8.3 0.48 ± 0.28 230±166 l09±53f 80±26 14.4 ± 4.7
8.43 ± 3.32 2010±793 224±93 19.7± lO.6t 79.4 ± 29.5 92.2 ± 42.2 35.4 ± 19.7 14.2± l0.7 0.46 ± 0.35t 308±161 76±33 1 1.9 ± S.2t
8. from intakes from intakes
in vegetarians, in vegetarians,
p < 0.002 (protected p < 0.05 (protected
salt intake, alcohol drinking, and smoking habits. Mean systolic and diastolic blood pressures fell significantly during the vegetarian periods in both experimental groups and rose again in the group which reverted to the omnivorous diet (Fig 3) whereas the control group showed no change after the initial familiarization period. Adjustment of the blood pressure changes for age, obesity, heart rate, weight change, and initial blood pressure showed a reversible diet-related decrease of the order of 5-6 mmHg systolic and 2-3 mmHg diastolic. Again, the blood pressure changes were unrelated to urinary Na cxcretion or estimated dietary Na intake. Compliance with
z
least significant least significant
difference difference
test between log-transformed test between log-transformed
intakes). intakes).
the diets
was confirmed by measurement of urinary 3methylhistidine, an amino-acid found predominantly in meat protein. Twenty-four hour dietary diaries obtained each week indicated nutrient changes (Fig 4) corresponding to the diets ofthe Seventh-day Adventist vegetarians(l8). Taken in conjunction with the epidemiological data, this intervention study provides strong cvidence for a direct blood pressure-lowering effect of a lactoovovegetarian diet. One possible confounding factor in this trial was that the subjects were not blind to the dietary changes. Thus theoretically the vegetarian diets may have exercised a placebo-like effect on blood pressures. Although such an effect cannot be excluded, the eagerness with which subjects resumed a meat diet suggests greater stress during the vegetarian periods and mitigates against this possibility. Margetts et al (19) in Perth subsequently demonstrated a blood pressure-lowering effect of a vegetarian diet in untreated mild hypertensive subjects with a study design similar to that described above. The results of this
I TABLE Average
2 home
blood
pressures
z
in
vegetarians
and omnivores*
Men
Systolic A$T0uc seu
Omnivores
(n=23)
(n=23)
111.9±7.0 70. 1 ± 6.7
Diastolic
Women
Vegetarians
Vegetarians
Omnivores
(n24)
(n-24)
98.2±7.3 65.8 ± 8.2
116.1 ±7.3t 71.2 ± 8.6
103.8±9.Ot 73.4 ± 6.9f
sITouc (..-..)
-
S
Average
ofduplicate
determinations
(on rising, at lunch time, on arriving FIG 2. Cumulative frequency distributions ofsystolic and diastolic blood pressure (BP) in SDA vegetarians (-) and Mormon omnivores (---) aged 25-44 y. For study details see Rouse et al (8).
arei±
made
on
home from
four
work,
occasions
during
and on retiring).
the
day
Results
SD.
t 5ignificant difference between omnivores
and
vegetarians,
p
