Prospective analysis of vitamin D and endometrial cancer risk.

BACKGROUND This is the first prospective cohort analysis on the association between vitamin D and endometrial cancer incorporating time-varying predicted plasma 25-hydroxyvitamin D [25(OH)D]. METHODS The prospective cohort analysis of predicted 25(OH)D and total dietary vitamin D intake used the Cox proportional hazards model, and involved 644 incident endometrial cancer events from 1986 to 2006 in the Nurses' Health Study. Genotyping and unconditional logistic regression were carried out on 572 endometrial cancer cases and their matched controls on 12 single nucleotide polymorphisms (SNPs) in vitamin D-related genes. RESULTS There was no significant association between predicted 25(OH)D and endometrial cancer incidence, with the hazard ratio for the highest (versus the lowest) quintile of predicted 25(OH)D as 1.00 (95% CI 0.73-1.36) (p-trend = 0.33). There was also no significant association involving total dietary vitamin D. No significant associations between any of the vitamin D-related SNPs and endometrial cancer were observed. CONCLUSION Both predicted 25(OH)D and total dietary vitamin D intake were not associated with endometrial cancer incidence. These results suggest that vitamin D may not protect against the development of endometrial cancer. However, the low and narrow vitamin D exposure range in the cohort may limit generalizability of the results.