A study published online Feb. 24 in JAMA Internal Medicine added yet more ammunition to the argument, “Eat your vegetables.” The meta-analysis found an association between vegetarian diets and lower blood pressure (BP) compared with omnivorous diets.

Yoko Yokoyama, MD, PhD, of the National Cerebral and Cardiovascular Center in Osaka, Japan, and colleagues, noted that randomized clinical trials comparing consumption of the two types of diets have had conflicting results for BP reduction. Observational studies have favored plant-based diets high in vegetable and fruit intake over diets that include meat, but many had small sample sizes and other limitations.

Using MEDLINE and Web of Science, the researchers identified seven clinical trials and 22 observational studies conducted between 1946 and 2013 and 1900 and 2013, respectively, that compared diets and included systolic and diastolic BP measures. The clinical trials enrolled a total of 311 participants and the observational studies included a total of 21,604 participants.

The meta-analysis of clinical trials showed a reduction in mean systolic and diastolic BP of 4.8 mm Hg and 2.2 mm Hg with vegetarian diets compared with omnivorous diets. The reduction was even greater in a separate meta-analysis of observational studies: 6.9 mm Hg and 4.7 mm Hg. They reported lower BP in all subgroups, although the differences were not significant in some subgroups.

Yokoyama and colleagues listed a number of possible reasons for the association between vegetarian diet and lower BP. Compared with omnivores, vegetarians tend to have lower body mass indexes, potassium-rich food sources and diets with less saturated fatty acids and more polyunsaturated fatty acids, for instance.

Their focus on dietary patterns rather than supplements or dietary manipulation makes the findings applicable to the general population, they proposed. “Further studies are required to clarify which types of vegetarian diets are most strongly associated with lower BP. Research into the implementation of such diets, either as public health initiatives aiming at the prevention of hypertension or in clinical settings, would also be of great potential benefit.”