Vitamin D Fails To Reduce Cancer Risk in Postmenopausal Women

Supplementation with vitamin D3 and calcium did not significantly reduce the risk of cancer among postmenopausal women, according to a randomized, controlled study published in JAMA.

Some studies showed an inverse relationship between vitamin D levels and cancer risk. The purpose of this trial was to evaluate the effect of vitamin D3 supplementation on cancer risk. This trial randomly assigned 2303 postmenopausal women to receive 2000 IU of vitamin D3 and 1500 mg of calcium per day or placebo for 4 years, with follow-up up visits every 6 months.

At baseline, the mean age was 65, 99% were non-Hispanic Caucasian, and the mean serum 25-hydroxyvitamin D level was 33 ng/mL. The mean serum 25-hydroxyvitamin D levels rose to 43.9 ng/mL by 12 months and was maintained during the 4-year study. In the placebo group, the mean serum 25-hydroxyvitamin D level remained around 31 ng/mL throughout the study.

At 4 years, 3.89% of women in the vitamin D3 group and 5.58% in the placebo group were diagnosed with cancer (difference, 1.69%; 95% CI, -0.06-3.46%; P = .06), resulting in an incidence of 0.042 (95% CI, 0.032-0.056) and 0.06 (95% CI, 0.048-0.076; P = .06), respectively. Vitamin D supplementation was not associated with reduced cancer risk with a hazard ratio of 0.70 (95% CI, 0.47-1.02). The lack of association may be a result of the higher baseline serum levels of 25-hydroxyvitamin D compared with the general US population, according to the authors.