Nearly 26,000 participants, over five years, testing two of the most widely used supplements in the world against cardiovascular events, cancer, and death. Here is what the trial actually found on each endpoint.
VITAL (VITamin D and OmegA-3 TriaL) randomized 25,871 U.S. adults — men 50+, women 55+, without a history of cancer or cardiovascular disease at enrollment — to one of four arms: vitamin D3 (2000 IU/day), marine omega-3 fatty acids (1g/day), both, or double placebo, in a 2×2 factorial design. Median follow-up was 5.3 years. Results were published in the New England Journal of Medicine in 2018 and 2019.
Neither vitamin D nor omega-3 significantly reduced the trial's co-primary endpoints — major cardiovascular events (MACE) or invasive cancer of any type — versus placebo. Neither significantly reduced all-cause mortality. On the primary questions the trial was designed to answer, both supplements were negative in this general, largely nutrient-replete population.
Two findings drew significant follow-on attention. Vitamin D showed a statistically significant reduction in cancer death specifically (a secondary endpoint), more pronounced with longer follow-up. Omega-3 showed a significant reduction in myocardial infarction in a subgroup with low baseline fish intake (an exploratory, non-prespecified-as-primary subgroup analysis).
Both are genuine, statistically real findings from a well-conducted trial — but both are secondary or subgroup results, which carry more risk of chance findings than a prespecified primary endpoint, and both need independent replication before being treated with the same confidence as a primary result.
VITAL is a negative trial on its primary endpoints and a genuinely informative one on its secondary findings. It does not support broad vitamin D or omega-3 supplementation for cardiovascular or all-cause mortality prevention in a general, nutrient-replete population, while leaving open real, narrower questions (cancer mortality for vitamin D; MI risk in low-fish-intake individuals for omega-3) that subsequent research has continued to investigate.
This information is provided for educational reference only and does not constitute medical advice or a treatment recommendation.