Vitamin D intake, blood 25(OH)D levels, and breast cancer risk or mortality: a meta-analysis

Background: Experimental studies suggest potential anti-carcinogenic properties of vitamin D against breast cancer risk, but the epidemiological evidence to date is inconsistent. Methods: We searched MEDLINE and EMBASE databases along with a hand search for eligible studies to examine the association between vitamin D status (based on diet and blood 25-hydroxyvitamin D (25(OH)D)) and breast cancer risk or mortality in a meta-analysis. A random-effect model was used to calculate a pooled adjusted relative risk (RR). Results: A total of 30 prospective studies (nested case-control or cohort) were included for breast cancer incidence (n = 24 studies; 31 867 cases) or mortality (n = 6 studies; 870 deaths) among 6092 breast cancer patients. The pooled RRs of breast cancer incidence for the highest vs the lowest vitamin D intake and blood 25(OH)D levels were 0.95 (95% CI: 0.88-1.01) and 0.92 (95% CI: 0.83-1.02), respectively. Among breast cancer patients, high blood 25(OH)D levels were significantly associated with lower breast cancer mortality (pooled RR = 0.58, 95% CI: 0.40-0.85) and overall mortality (pooled RR = 0.61, 95% CI: 0.48-0.79). There was no evidence of heterogeneity and publication bias. Conclusions: Our findings suggest that high vitamin D status is weakly associated with low breast cancer risk but strongly associated with better breast cancer survival.