Can increasing the prevalence of vegetable-based diets lower the risk of osteoporosis in postmenopausal subjects? A systematic review with meta-analysis of the literature.

OBJECTIVES Several epidemiological investigations have assessed the association between vegetable-based diet intake (VDI) and risk of osteoporosis in postmenopausal subjects (OPS), but the outcomes have been inconsistent. We performed a review of the updated literature to evaluate this correlation. METHODS We searched for relevant studies published in September 2018 or earlier. Two researchers conducted eligibility assessment and data extraction. Discrepancies were resolved through consultation with a third expert. Pooled odds ratios (ORs) were calculated with 95% confidence intervals (CIs). RESULTS Ten studies, which included 14,247 subjects, were identified. On comparing the highest category of VDI consumption with the lowest category of VDI consumption, the pooled OR for OPS was 0.73 (95% CI = 0.57-0.95), i.e., participants with a higher intake of vegetables had a 27% (95% CI = 5-43%) lower risk of OPS. Significant benefits were found on subgroup analyses of case-control studies (OR, 0.61 [95% CI, 0.48-0.78]), but not on subgroup analyses of cross-sectional studies (OR, 0.82 [95% CI, 0.57-1.16]). The synthesized effect estimates were in the direction of decreased risk of OPS on subgroup analyses of the femoral region (OR, 0.57, 95% CI = 0.41-0.80) and the lumbar spine (OR = 0.55, 95% CI = 0.38-0.81), but not on subgroup analyses of the calcaneus (OR = 0.85, 95% CI = 0.33-2.16) and the lumbar and/or femoral region (OR = 1.04, 95%CI = 0.79-1.38). Positive results were observed on pooled analyses of the Dual energy X-ray absorptiometry (DEXA) measurement method (OR, 0.72 [95% CI, 0.54-0.95]), but not on pooled analyses of the Standardized Quantitative Ultrasound (QUS) measurement method (OR, 0.85 [95% CI, 0.33-2.16]). This might have resulted from a type II error due to wide confidence intervals and less number of included studies. CONCLUSION This meta-analysis seemingly confirms that higher consumption of VDI was associated with a lower risk of OPS. Taken together, these results highlight the need for future high-quality design-based trials on quantified vegetable intake and OPS.