Vegetarians have lower measured blood pressures and less hypertension than non-vegetarians
By Barry Manembu
LOMA LINDA, Calif. – Diet affects blood pressure levels and vegetarians (vegans and lacto-ovo vegetarians) have less hypertension than non-vegetarians, according to researchers at the Adventist Health Study, Loma Linda University. The results are published in Public Health Nutrition.
Over the last thirty years, many studies have examined the effects of a vegetarian diet on blood pressure. Yet, most of these have been short-term, limited in size, and not on diverse subjects. They also tend to focus on the lacto-ovo vegetarian rather than the vegan diet. This particular study, aimed to evaluate the association between vegetarian dietary pattern and both blood pressure and diagnosis of hypertension, differs from the previous ones – it presents results of a cross-sectional comparison within a relatively large and diverse group, where the vegetarian and non-vegetarian habits were generally long-term, and where vegetarians are divided to vegans and non-vegans.
The researchers analyzed data from calibration study subjects within the Adventist Health Study-2 (AHS-2) cohort. In this particular analysis, the researchers assessed a representative sample of 500 white individuals, randomly selected from the parent cohort (AHS-2) by the church, and then compared their food frequency questionnaire (FFQ) responses about diet to measured blood pressure levels.
Blood pressure and body mass index (BMI) of the calibration study subjects were measured, and urine samples were collected. A food frequency questionnaire was also used to assess dietary pattern; criteria were established for vegan, lacto-ovo vegetarian, partial vegetarian, and omnivorous dietary pattern. The main result: vegan and lacto-ovo vegetarian had lower systolic and diastolic blood pressure than omnivorous Adventists. Moreover, after making adjustment for age and gender, systolic blood pressure was significantly lower in vegans/lacto-ovo vegetarians when compared to non-vegetarians, and results were broadly similar for diastolic blood pressure.
Hypertension was defined as either an average of systolic blood pressure of more than 139 mm Hg or more than 89 mm Hg of diastolic blood pressure. People taking antihypertensive medications were also categorized as having hypertension. Researchers found that the dietary pattern related to hypertension corresponded with their reported blood pressure.
BMI, a measure of body size, also significantly associated with both systolic and diastolic blood pressure, as higher BMI predicted higher blood pressures. The lower chance of hypertension in vegan, lacto-ovo, and partial vegetarians was diminished substantially when BMI was added to the model, suggesting that the effect of diet to reduce BMI was partially responsible for the effects of diet on hypertension.
“Our study extends and supports previous evidence that diet affects measured blood pressure levels, both systolic and diastolic. This appears to be long-lasting as our subjects, coming from a population that includes a wide variety of age, social economic status, and both gender, have maintained these dietary habits over at least one year and will continue to maintain them over many years for the most part,” explains lead researcher Betty J. Pettersen, Ph.D.
"The percent overweight or obese in this population was lower than in the general U.S. population and while our results are adjusted for these factors, it seems likely that the effect of a vegetarian diet to reduce body weight is one mechanism partially responsible for the blood pressure effect," Dr. Pettersen adds. "However, some additional effect probably still remains."
Beyond BMI, which dietary factors in the vegetarian may account for effects on blood pressure levels is not well understood. One thing for sure is that vegetarians have a higher fiber and potassium intake as a result of their greater consumption of fruits, vegetables, nuts, and whole-grain products. Consumption of a potassium-rich diet has a natriuretic effect – causing natriuresis, the excretion of large amounts of sodium in urine – and diets that are high in potassium usually are low in sodium, as long as unprocessed foods are consumed. Sodium (mainly as salt) is known to raise blood pressure.
"Low calcium or dairy intake has also been associated with slightly higher blood pressures by others. Our results are not consistent with this as vegans who avoid dairy products have the least hypertension, although further evidence should be gathered on this group" says Gary Fraser MD, Ph.D., principal investigator of AHS-2. "Americans may benefit from a diet containing more plant foods to lower blood pressure levels."
This research was funded by a grant from the National Cancer Institute (NCI), a division of National Institutes of Health (NIH), the federal agency for health research.
Adventist Health Study-2 (AHS-2) is one of the largest and most exciting health studies of its kind ever designed and will have national importance and international significance. It is a cohort study of over 96,000 Seventh-day Adventists in the U.S. and Canada who enrolled between 2002 and 2007. Adventists, due in part to their unique dietary habits, have a lower risk than other Americans of heart disease, several cancers, and probably high blood pressure, arthritis, and diabetes. This, along with their wide variety of dietary habits, provides a special opportunity for careful research to answer a host of scientific questions about how diet (and other health habits) may change the risk of suffering from many chronic diseases.
Two previous studies on Adventist health involving 24,000 and 34,000 Californian Adventists have been directed from Loma Linda University over the last 40 years. These have been among the first to raise scientific awareness of the close relationship between diet and health. This groundbreaking work has brought visibility and accolades to the lifestyle recommended by Seventh-day Adventists from both the scientific and lay communities. AHS-2 is conducted by researchers at Loma Linda University School of Public Health. For more information, visit www.adventisthealthstudy.org.