Abstract
Importance: Previous studies have suggested an association between vegetarian diets and lower blood pressure (BP), but the relationship is not well established. Objective: To conduct a systematic review and meta-analysis of controlled clinical trials and observational studies that have examined the association between vegetarian diets and BP. Data Sources: MEDLINE and Web of Science were searched for articles published in English from 1946 to October 2013 and from 1900 to November 2013, respectively. Study Selection: All studies met the inclusion criteria of the use of (1) participants older than 20 years, (2) vegetarian diets as an exposure or intervention, (3) mean difference in BP as an outcome, and (4) a controlled trial or observational study design. In addition, none met the exclusion criteria of (1) use of twin participants, (2) use of multiple interventions, (3) reporting only categorical BP data, or (4) reliance on case series or case reports. Data Extraction and Synthesis: Data collected included study design, baseline characteristics of the study population, dietary data, and outcomes. The data were pooled using a random-effects model. Main Outcomes and Measures: Net differences in systolic and diastolic BP associated with the consumption of vegetarian diets were assessed. Results: Of the 258 studies identified, 7 clinical trials and 32 observational studies met the inclusion criteria. In the 7 controlled trials (a total of 311 participants; mean age, 44.5 years), consumption of vegetarian diets was associated with a reduction in mean systolic BP (-4.8 mm Hg; 95% CI, -6.6 to -3.1; P < .001; I² = 0; P = .45 for heterogeneity) and diastolic BP (-2.2 mm Hg; 95% CI, -3.5 to -1.0; P < .001; I² = 0; P = .43 for heterogeneity) compared with the consumption of omnivorous diets. In the 32 observational studies (a total of 21 604 participants; mean age, 46.6 years), consumption of vegetarian diets was associated with lower mean systolic BP (-6.9 mm Hg; 95% CI, -9.1 to -4.7; P < .001; I² = 91.4; P < .001 for heterogeneity) and diastolic BP (-4.7 mm Hg; 95% CI, -6.3 to -3.1; P < .001; I² = 92.6; P < .001 for heterogeneity) compared with the consumption of omnivorous diets. Conclusions and Relevance: Consumption of vegetarian diets is associated with lower BP. Such diets could be a useful nonpharmacologic means for reducing BP.
Generated Summary
This meta-analysis systematically reviewed controlled clinical trials and observational studies to assess the association between vegetarian diets and blood pressure (BP). The research aimed to clarify the relationship between vegetarian diets and BP and provide an estimate of the effect size of vegetarian diets on BP. The study included data from MEDLINE and Web of Science, searching for articles published in English from 1946 to October 2013 and from 1900 to November 2013, respectively. The analysis included controlled clinical trials and observational studies examining the association between vegetarian diets and BP, with participants older than 20 years and excluding those using twin participants or multiple interventions. Data collected included study design, baseline characteristics of the study population, dietary data, and outcomes. The main outcomes and measures were net differences in systolic and diastolic BP associated with the consumption of vegetarian diets.
Key Findings & Statistics
The meta-analysis included 7 clinical trials and 32 observational studies. The clinical trials involved a total of 311 participants, with a mean age of 44.5 years, while the observational studies included 21,604 participants with a mean age of 46.6 years.
- In the 7 controlled trials, the consumption of vegetarian diets was associated with a reduction in mean systolic BP of -4.8 mm Hg (95% CI, -6.6 to -3.1; P < .001) and diastolic BP of -2.2 mm Hg (95% CI, -3.5 to -1.0; P < .001) compared with the consumption of omnivorous diets.
- In the 32 observational studies, consumption of vegetarian diets was associated with lower mean systolic BP (-6.9 mm Hg; 95% CI, -9.1 to -4.7; P < .001) and diastolic BP (-4.7 mm Hg; 95% CI, -6.3 to -3.1; P < .001) compared with the consumption of omnivorous diets.
- The study also notes that in individuals aged 40 to 70 years, each increment of 20 mm Hg in systolic BP or 10 mm Hg in diastolic BP is associated with more than twice the risk of cardiovascular disease across the BP range from 115/75 to 185/115 mm Hg.
- The subgroup analysis revealed that in the clinical trials, no heterogeneity was found in any subgroup and the estimated effect sizes were very similar.
- For observational studies, subgrouping reduced heterogeneity in most cases, and vegetarian diets were associated with lower BP regardless of subgroup, although effect sizes were attenuated in some groups.
Other Important Findings
- The relationship between blood pressure (BP) and cardiovascular disease risk is continuous, consistent, and independent of other risk factors.
- The study highlights that consumption of vegetarian diets is associated with lower BP, and these diets could be a useful nonpharmacologic means for reducing BP.
- The research indicates that dietary modifications have been shown to be particularly effective in preventing and managing hypertension.
- In the clinical trials, consumption of vegetarian diets was associated with a mean reduction in systolic BP (-4.8 mm Hg; 95% CI, -6.6 to -3.1; P < .001; I² = 0; P = .45 for heterogeneity) and diastolic BP (-2.2 mm Hg; 95% CI, -3.5 to -1.0; P < .001; I² = 0; P = .43 for heterogeneity) compared with the consumption of omnivorous diets.
- In the 32 observational studies, consumption of vegetarian diets was associated with lower mean systolic BP (-6.9 mm Hg; 95% CI, -9.1 to -4.7; P < .001; I² = 91.4; P < .001 for heterogeneity) and diastolic BP (-4.7 mm Hg; 95% CI, -6.3 to -3.1; P < .001; I² = 92.6; P < .001 for heterogeneity) compared with the consumption of omnivorous diets.
- The study also noted that in the observational studies, subgrouping reduced heterogeneity in most cases, and vegetarian diets were associated with lower BP regardless of subgroup, although effect sizes were attenuated in some groups.
Limitations Noted in the Document
- Heterogeneity among the observational studies was high.
- The meta-analysis carried forward design limitations of the included studies, including small sample sizes and the use of cross-sectional designs in observational studies.
- Some observational studies did not adjust for lifestyle factors, such as alcohol intake or physical activity level.
- The foods that make up vegetarian diets and the nutrient composition of the diets differ from person to person and from country to country.
Conclusion
The meta-analysis found that the consumption of vegetarian diets is associated with lower BP compared with the consumption of omnivorous diets. The study indicated an overall difference in systolic BP of -4.8 mm Hg in controlled trials and -6.9 mm Hg in observational studies, and for diastolic BP, the differences were -2.2 mm Hg in controlled trials and -4.7 mm Hg in observational studies. The authors suggest these effect sizes are similar to those observed with commonly recommended lifestyle modifications, such as adoption of a low-sodium diet or a weight reduction of 5 kg, and are approximately half the magnitude of those observed with pharmaceutical therapy, such as administration of angiotensin-converting enzyme inhibitors to individuals with hypertension. The authors conclude that consumption of vegetarian diets is associated with lower BP and that further studies are required to clarify which types of vegetarian diets are most strongly associated with lower BP. They suggest that research into the implementation of such diets, either as public health initiatives aiming at prevention of hypertension or in clinical settings, would also be of great potential value. The study’s findings support the idea that vegetarian diets could be a useful nonpharmacologic means for reducing BP.