Aims: To examine the association between vitamin D status and risk of breast cancer in an Australian population of women.
Methods: Observational case-control study set at Westmead Breast Cancer Institute, Westmead Hospital, Sydney, Australia. 214 women newly diagnosed women with breast cancer were matched to 852 controls by socioeconomic status, decade of age and season of testing, all tested at the same laboratory tested between August 2008 and July 2010. Circulating 25-hydroxyvitamin D concentration (25OHD3) was defined as sufficient (≥75nmol/L), insufficient (50-74nmol/L), deficient (25-49nmol/L) or severely deficient (<25nmol/L) status. The difference in mean 25OHD between cases and controls was estimated by independent T-tests. Odds ratios and 95% confidence intervals for the risk of breast cancer by 25OHD3 concentration were estimated by Cox regression.
Results: Mean plasma 25OHD3 was significantly lower in cases versus (vs) controls overall (54.3 vs 64.0nmol/L,) and during summer (53.1 vs 68.6nmol/L), winter (54.1 vs 69.0nmol/L) and spring (45.7 vs 52.9; all P<0.001). In a Cox regression model plasma 25OHD3 was inversely associated with odds of breast cancer. Compared to subjects with sufficient 25OHD3, the odds of breast cancer (95% confidence interval) was 2.3 (1.3-4.3), 2.5 (1.6-3.9) and 2.5 (1.6-3.8) for subjects categorized as severely deficient, deficient or insufficient vitamin D status, respectively.
Conclusion: The results of this observational case control study indicate 25OHD3 concentration below 75nmol/L at diagnosis was associated with a significantly higher risk of breast cancer. Further randomised trials are required to assess whether achieving a 25OHD3 concentration above 75nmol/L decreases the risk of breast cancer.