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
Generated Summary
This meta-analysis investigated the association between vegetarian diets and blood pressure (BP) using a systematic review of controlled clinical trials and observational studies. The study searched MEDLINE and Web of Science for articles published in English, adhering to specific inclusion and exclusion criteria. The primary objective was to evaluate the relationship between vegetarian diets and BP, utilizing net differences in systolic and diastolic BP as the main outcomes. Data extraction included study design, baseline characteristics, dietary data, and outcomes, which were pooled using a random-effects model. The study included a total of 7 clinical trials and 32 observational studies that met the inclusion criteria, with results analyzed to provide a valid estimate of the effect of vegetarian diets on BP. The study considered the association between vegetarian diets and BP with cardiovascular disease risk factors, and its potential use as a nonpharmacologic means for reducing BP. The research aimed to clarify the nature of this association and provide a valid estimate of the effect size regarding the effects of consumption of vegetarian diets on BP, both of which could prove useful in formulating dietary guidance, the study included assessment of the effects of vegetarian diets on BP, with the aim of possibly formulating dietary guidance.
Key Findings & Statistics
- Of 258 studies identified, 7 clinical trials and 32 observational studies met the inclusion criteria.
- In the 7 controlled trials (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 (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.
- 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 (Figure 2).
- In the 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 consumption of omnivorous diets (Figure 3 and Figure 4).
- In the meta-regression investigating the sources of heterogeneity in the observational trials, the potential sources were sex (proportion of men) (ẞ coefficient, -0.03; P < .001), baseline systolic BP (-0.13; P = .003), baseline diastolic BP (-0.30; P < .001), sample size (0.001; P < .001), and BMI (-0.46; P = .02).
Other Important Findings
- The relationship between blood pressure (BP) and cardiovascular disease risk is continuous, consistent, and independent of other risk factors.
- A substantial body of evidence supports the role of modifiable factors, including diet, body weight, physical activity, and alcohol intake, in the risk of developing hypertension.
- Vegetarian diets are defined as dietary patterns that exclude or rarely include meats; some vegetarian diets include dairy products, eggs, and fish. All vegetarian diets emphasize foods of plant origin, particularly vegetables, grains, legumes, and fruits.
- The study suggests that the association between vegetarian diets and lower BP in adults is stronger among men and those with higher baseline BP and BMI.
- 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.
- Lower systolic BP values were reported in the predominantly (50%-99%) male subgroups compared with the 100% female subgroups.
- In the one-study-removed analysis, results were largely unchanged, with BP differences between the vegetarian and comparison groups ranging from -5.3 to -3.5 mm Hg for systolic BP and -2.9 to -1.8 mm Hg for diastolic BP in clinical trials (all results, P < .05) and from -7.2 to -6.3 mm Hg for systolic BP and -5.0 to -4.3 mm Hg for diastolic BP for observational studies (all results, P < .001).
- For observational studies, visual examination of the funnel plot revealed that larger trials that reported generous reductions in systolic BP were possibly overrepresented.
Limitations Noted in the Document
- Although no heterogeneity existed among the controlled trials, heterogeneity was high among the observational studies.
- Most notable in this regard are small sample sizes and the fact that all observational studies used cross-sectional rather than prospective designs; however, the latter limitation is partially compensated for by the inclusion of several randomized clinical trials.
- Some of the observational studies did not adjust for lifestyle factors, such as alcohol intake or physical activity level.
- 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 findings of this meta-analysis indicate that the consumption of vegetarian diets is associated with lower BP. The study’s results are consistent with prior research, including those from the Dietary Approaches to Stop Hypertension (DASH) study, which also recognized the benefits of a diet rich in vegetables and fruits. This study reinforces the understanding of how specific dietary and lifestyle factors, such as obesity, sodium intake, and alcohol use, can influence BP, and that the adoption of vegetarian diets can reduce BP. The study noted that the association between vegetarian diets and lower BP in adults is stronger among men and those with higher baseline BP and BMI. The analysis also showed lower systolic and diastolic BP in vegetarians compared to omnivores, suggesting that vegetarian diets could serve as a nonpharmacologic means for reducing BP. The study further points out the importance of diet in cardiovascular health and the potential for lifestyle modifications, such as vegetarian diets, to have a significant impact on BP. Moreover, the study suggests that a shift to vegetarian diets can be a useful method for lowering BP, thus potentially preventing and managing hypertension. Overall, the meta-analysis underscores the potential of vegetarian diets as a means of lowering BP, which may influence dietary guidelines and offer insights into public health strategies for hypertension prevention and management. However, further studies are needed to clarify specific aspects of vegetarian diets and their effects on BP.
IFFS Team Summary
- 311 subject in 7 clinical trials, and over 21000 subjects in 32 observational studies mean age about 44-46 years old
- showed systolic and diastolic BP lowering
- studies only vegetarian diets, would possibly have stronger results if included vegans subgroup