Manson JE, et al. - In this large primary-prevention trial, researchers assessed whether supplementation with vitamin D decreases the risk of cancer (except nonmelanoma skin cancer) or cardiovascular disease among. Compared with placebo, supplementation with vitamin D₃ did not result in a significantly lower incidence of invasive cancer of any type or a composite of major cardiovascular events (myocardial infarction, stroke, and death from cardiovascular causes). In addition, the intervention did not prompt a lower incidence of total deaths from cancer or a lower incidence of breast, prostate, or colorectal cancer vs placebo.

Methods

• Among US men aged ≥ 50 years and women aged ≥ 55 years, researchers conducted a nationwide, randomized, placebo-controlled trial, with a two-by-two factorial design, of vitamin D₃ at a dose of 2000 IU/day and marine n−3 (also known as omega-3) fatty acids at a dose of 1 g/day for the prevention of cancer and cardiovascular disease.
• Invasive cancer of any type and major cardiovascular events were primary end points.
• Site-specific cancers, death from cancer, and additional cardiovascular events were included secondary end points.

Results

• In total, 25,871 participants were randomized, including 5,106 black participants.
• Vitamin D supplementation did not result in a lower risk of either of the primary endpoints.
• Cancer was diagnosed among 1,617 participants during a median follow-up of 5.3 years.
• The investigators observed a major cardiovascular event in 805 study participants.
• The hazard ratios were as follows: for death from cancer (341 deaths), 0.83 (95% CI, 0.67 to 1.02); for breast cancer, 1.02 (95% CI, 0.79 to 1.31); for prostate cancer, 0.88 (95% CI, 0.72 to 1.07); for colorectal cancer, 1.09 (95% CI, 0.73 to 1.62); for the expanded composite end point of major cardiovascular events plus coronary revascularization, 0.96 (95% CI, 0.86 to 1.08); for myocardial infarction, 0.96 (95% CI, 0.78 to 1.19); for stroke, 0.95 (95% CI, 0.76 to 1.20); and for death from cardiovascular causes, 1.11 (95% CI, 0.88 to 1.40) in the analyses of secondary end points.
• The hazard ratio was 0.99 (95% CI, 0.87 to 1.12) in the analysis of death from any cause (978 deaths).
• There were no excess risks of hypercalcemia or other adverse events.