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Vegetarian diets and blood pressure.

Vegetarian diets and blood pressure

Yokoyoma Y, Nichimura K, Barnard N, Takegami M, Watanabe M, Sekikawa A, Okamura T, Miyamoto Y. 2014. Vegetarian diets and blood pressure: a meta-analysis. JAMA Intern Med 174(4):577-587

Blood pressure (BP) is a continuous, consistent and individual risk factor for cardiovascular disease with known modifiable risk factors including diet, bodyweight, physical activity and alcohol intake. Observational studies have found consumption of vegetarian diets is associated with a lower prevalence of hypertension, but randomised clinical trials have produced conflicting results as to whether the adoption of a vegetarian diet reduces BP. To further understand the association between vegetarian diets and BP, the authors performed a meta-analysis of studies investigating this.

MEDLINE and Web of Science were searched for articles published in English containing keywords for vegetarian diets and for blood pressure. The reference lists of the retrieved articles were reviewed for additional articles. Studies eligible for inclusion into the meta-analysis had participants older than 20 years, had a vegetarian diet defined as a diet generally excluding or rarely including meats, sufficient data for systolic and diastolic BP and comparisons to control, and use of a controlled trial or observational study design. Exclusion criteria included twin studies, multiple interventions such as lifestyle as well as dietary modification, reporting only categorical BP data or reliance on case reports or case series.

In total 258 studies were retrieved with seven clinical trials and 32 observational studies meeting the inclusion criteria. The seven clinical trials included a total of 311 participants with a mean age of 44.5 years. All studies were open-controlled trials conducted for six weeks or longer (mean 15.7 weeks). Vegan diets were examined in two trials, a lacto-vegetarian diet in one, and lacto-ovo-vegetarian diets in the remaining four. In all but one study, the food was provided to participants. In the clinical trials, consumption of vegetarian diets was associated with a significant mean reduction in systolic BP of 4.8mmHg and reduction of diastolic BP of 2.2mmHg compared with consumption of omnivorous diets.

The 32 observational studies included 21,604 participants with a mean age of 46.6 years. Participants had been following vegetarian diets for more than one year in 22 of the studies. Five studies focused on vegan diets, 2 on lacto-vegetarian, 10 on lacto-ovo-vegetarian diets and 15 on mixed types (vegan, lacto, lacto-ovo, pesco and/or semi-vegetarian). Diet intake was measured through food questionnaire or 24-hour diet recalls for most observational studies. Consumption of vegetarian diets in the observational studies was associated with a significant mean reduction in systolic BP of 6.9mmHg and diastolic BP of 4.7mmHg compared to consumption of omnivorous diets.

The effect size of the reductions in BP observed from both the clinical trials and observational studies analyses are similar to other commonly recommended lifestyle modifications such as reduced salt intake or weight reduction of 5kg, and approximately half the magnitude of reduction observed with pharmaceutical therapies including ACE-inhibitors. The authors note that a reduction in systolic BP of 5mm Hg would be expected to result in a 7%, 9% and 14% overall reduction in mortality due to all causes, coronary heart disease, and stroke, respectively. Authors suggest a number of factors might contribute to the BP reductions associated with vegetarian diets including lower BMIs and lower obesity levels, increased potassium intake and lowered salt intake with vegetarian diets, proportionally lower intake of saturated fatty acids and higher intake of polyunsaturated fatty acids, and higher intake of vegetable proteins.

Strengths of the meta-analysis include a large overall sample size and a focus on dietary interventions that are reasonably accessible to the general population. Limitations include the high heterogeneity in the observational and a lack of prospective studies. Studies from languages other than English might have provided further information and increased the population to which these findings may be relevant. The inclusion of the variety of diets ranging from vegan to semi-vegetarian provides insight in line with real world setting, but future research to understand if specific vegetarian diet types confer additional benefits over others would be relevant.
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Author:Tester, Jodie
Publication:Australian Journal of Herbal Medicine
Article Type:Report
Geographic Code:8AUST
Date:Dec 1, 2014
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