Study finds calcium, vitamin D supplements may reduce cancer mortality in long term

For postmenopausal women, calcium and vitamin D (CaD) supplements may reduce cancer mortality and increase cardiovascular disease (CVD) mortality after more than 20 years of follow-up, according to a study published online March 12 in the Annals of Internal Medicine.

Cynthia A. Thomson, Ph.D., R.D., from the Mel and Enid Zuckerman College of Public Health at the University of Arizona in Tucson, and colleagues examined long-term health outcomes among postmenopausal women in the Women's Health Initiative CaD trial involving 36,282 women with no history of breast or colorectal cancer. Participants were randomly assigned to receive 1,000 mg calcium carbonate with 400 IU vitamin D₃ daily or placebo.

The researchers found that after a median cumulative follow-up of 22.3 years, women randomly assigned to CaD versus placebo had a reduction in cancer mortality (hazard ratio, 0.93), and an increase in CVD mortality (hazard ratio, 1.06). No overall effect was seen on other measures, including all-cause mortality. There was considerable variation observed in estimates of cancer incidence when stratified by whether participants reported supplement use before randomization, while no variation was seen for estimates in mortality, except for CVD mortality.

"Effects of vitamin D supplementation for cancer prevention may depend on achieving serum vitamin D concentrations above 50 nmol/L," the authors write. "Given the study design, we could not disentangle the added benefit or harms of supplementation with CaD in combination versus vitamin D alone, a topic worthy of future study."

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