Vitamin D and cancer risk in older women:
A population-based randomized 4-year study conducted in Nebraska enrolled 1179 women aged 55 years and older, with no known cancer. Participants were randomly assigned to 3 groups: 1) Placebo (calcium placebo plus vitamin D placebo, n=266); 2) calcium-only (1400 mg calcium citrate or 1500 mg calcium carbonate plus vitamin D placebo, n=416); and Calcium + D (1000 IU [25 mcg] vitamin D plus calcium [as above], n=403). Serum samples were analyzed for levels of 25(OH)D, vitamin D, at baseline and then yearly. Study results found 50 women developed non-skin cancer during the study: 13 in the first year, and 37 during the second to fourth years. The relative risk (RR) for the calcium + D group was 0.232 (confidence interval [CI], 0.09–0.60; P<.005), and the RR for the calcium-only group was 0.587 (95% CI, 0.29–1.21; P=.147) compared with the placebo group. Increasing the dose of vitamin D from the current standard of 400–600 IU per day to 1000 IU per day lowers future risk of cancer in women older than age 55 who do not get adequate vitamin D from sun exposure or diet. (24)