Effect of vegetarian diets on bone mineral density: a Bayesian meta-analysis.

BACKGROUND The association between vegetarian diets and bone mineral density (BMD) is controversial because of conflicting findings from previous studies. OBJECTIVE The aim of this study was to estimate the effect of vegetarian diets on BMD by using a meta-analytic approach. DESIGN A systematic electronic literature search was conducted to identify all relevant articles on the association between vegetarian diet and BMD. Nine studies of 2749 subjects (1880 women and 869 men) were included in the analysis. Traditional and Bayesian methods of meta-analysis were applied to synthesize the data. RESULTS Overall, BMD was approximately 4% lower in vegetarians than in omnivores (95% CI: 2%, 7%) at both the femoral neck and the lumbar spine. Compared with omnivores, vegans had a significantly lower lumbar spine BMD (6% lower; 95% CI: 2%, 9%), which was more pronounced than in lactoovovegetarians (2% lower; 95% CI: 1%, 4%). The probability that BMD was > or =5% lower in vegetarians than in omnivores (or approximately 0.3 SD) was 42% for the femoral neck and 32% for the lumbar spine. There was no evidence of publication bias. There was a moderate degree of between-study heterogeneity; the coefficient of heterogeneity varied between 46% and 51%. CONCLUSION The results suggest that vegetarian diets, particularly vegan diets, are associated with lower BMD, but the magnitude of the association is clinically insignificant.