In a nationwide trial, supplementation with vitamin D did not result in a lower incidence of invasive cancer or cardiovascular events than placebo. Researchers conducted a randomized, placebo-controlled trial with a 2-by-2 factorial design, of vitamin D3 (cholecalciferol) at a dose of 2000 IU per day and marine n-3 (omega-3) fatty acids at a dose of 1 g day for the prevention of cancer and CVD among men aged ≥50 years and women aged ≥55 in the US. Primary end points were invasive cancer of any type and major CV events. Secondary end points included site-specific cancers, death from cancer, and additional CV events. Among the findings:

• 25,871 participants underwent randomization (including 5,106 black participants).
• Supplementation with vitamin D was not associated with a lower risk of either cancer or CVD.
• During a median follow-up of 5.3 years, cancer was diagnosed in 1,617 participants (793 in the vitamin D group and 824 in the placebo group; hazard ratio 0.96).
• A major CV event occurred in 805 participants (396 in the vitamin D group and 409 in the placebo group; HR 0.97).
• In the analyses of secondary end points, the HRs were: for death from cancer, 0.83; for breast cancer, 1.02; for prostate cancer, 0.88; for colorectal cancer, 1.09; for the expanded composite end point of major CV events plus coronary revascularization, 0.96; for myocardial infarction, 0.96; for stroke, 0.95; and for death from CV causes, 1.11.