Vitamin D intake and breast cancer risk: a case-control study in Italy.

BACKGROUND Vitamin D has been suggested to play a protective role against several cancers, including breast cancer. PATIENTS AND METHODS We used data from a case-control study conducted in Italy from 1991 to 1994 to study the relation between dietary intake of vitamin D and breast cancer risk. Subjects were 2569 women with incident, histologically confirmed breast cancer and 2588 hospital controls. Odds ratios (ORs) and 95% confidence intervals (CIs) according to deciles of vitamin D intake were estimated by multiple logistic regression models. RESULTS After allowance for major risk factors for breast cancer and dietary covariates including calcium and energy intake, there was no association with vitamin D up to the seventh decile. Thereafter, the OR declined, so that the overall trend was statistically significantly inverse. The OR for subjects in the three highest deciles of consumption compared with those in the lowest ones combined was 0.79 (95% CI 0.70-0.90). Intake of vitamin D >3.57 microg or 143 IU appeared to have a protective effect against breast cancer. The inverse association was consistent across strata of menopausal status. CONCLUSIONS This study adds to the existing evidence that vitamin D intake in inversely associated with breast cancer risk.