Vegetarian Diets and Blood Pressure - A Meta-analysis

Yokoyama Y, Nishimura K, Barnard ND et al.
JAMA Intern Med. Published online February 24, 2014. doi:10.1001/jamainternmed.2013.14547

Background

The risk of developing hypertension is modifiable by means of changing diet, body weight, physical activity and alcohol intake, among which dietary changes appear particularly effective [1]. Consumption of vegetarian diets has been associated with a lower prevalence of hypertension in observational studies [2,3]. Randomised clinical studies investigating adoption of a vegetarian diet in relation to blood pressure (BP) have yielded conflicting data.
This meta-analysis aims to clarify the nature of the effect of a vegetarian diet on BP. 7 clinical trials and 32 observational studies met the inclusion criteria. A vegetarian diet was defined as a diet generally excluding or rarely including meats.

Main results

• Pooled results of the clinical trials show that consumption of vegetarian diets was associated with a mean reduction in systolic BP (-4.8 mmHg, 95%CI: -6.6 to -3.1, P<0.001) and in diastolic BP (-2.2 mmHg, 95%CI: -3.5 to -1.0, P<0.001) as compared to omnivorous diets.
• In the observational studies, pooled analysis revealed that consumption of vegetarian diets was associated with lower mean systolic BP (-6.9 mmHg, 95%CI: -9.1 to -4.7, P<0.001) and diastolic BP (-4.7 mmHg, 95%CI: -6.3 to  -3.1, P<0.001) than omnivorous diets.
• Substantial heterogeneity was seen between the observational studies. A meta-regression analysis revealed sex (proportion of men), baseline systolic and diastolic BP, sample size and BMI as potential sources of heterogeneity. The association between vegetarian diets and lower BP thus seem stronger among men and those with higher baseline BP and BMI, and in smaller studies.
• Analyses of subgroups in the observational data consistently showed that vegetarian diets were associated with lower BP, albeit with different effect sizes.
• In a one-study-removed sensitivity analysis results were largely unchanged.
• A funnel plot suggests that there was some publication bias in that smaller clinical trials reporting small reductions in systolic BP were possibly overrepresented, while larger observational trials reporting large reductions in systolic BP were possibly overrepresented.

Conclusion

This meta-analysis indicates that consumption of vegetarian diets is associated with lower BP as compared to consumption of omnivorous diets. The observed declines in systolic and diastolic BP are similar to those seen with commonly recommended lifestyle modifications, such as adoption of a low-sodium diet, or a weight reduction of 5 kg, and about half the magnitude of those observed with pharmaceutical therapy. Future studies may identify which types of vegetarian diets are most strongly associated with lower BP.

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