The VITAL trial

If you already have decent vitamin D levels, VITAL is the best evidence that 2000 IU a day did not prevent cancer, heart disease, fractures or depression. Its few positive signals, on cancer deaths, autoimmune disease and telomeres, are leads, not reasons to take it.

What the trial tested

The VITamin D and OmegA-3 TriaL (VITAL) randomised 25,871 US adults to 2000 IU a day of vitamin D3 or placebo, for a median of 5.3 years. Its two main questions were whether vitamin D lowered invasive cancer and major cardiovascular events (major heart and stroke events).^[1] The same trial also tested a marine omega-3 supplement against placebo; that half of the story is covered in Omega-3.

Vitamin D is a fat-soluble vitamin the skin makes in sunlight and that some foods and supplements supply; blood tests measure it as 25-hydroxyvitamin D. Most VITAL participants were not deficient to begin with,^[2] which matters for everything below: the trial says much less about people who are truly low.

The main results: null

• Cancer and heart disease. Neither main outcome improved. For major cardiovascular events the hazard ratio was 0.97, meaning the risk at any point was about the same as on placebo; the 95% confidence interval, the range where the true effect most plausibly lies, ran from 0.85 to 1.12.^[3]
• Death from any cause. No difference (hazard ratio 0.99, confidence interval 0.87–1.12).^[4]
• Fractures. 2000 IU a day did not lower fractures (hazard ratio 0.98).^[5]
• Depression. In 18,353 adults, vitamin D had no effect on new or recurring depression.^[6]

A 2026 modelling study re-ran VITAL and the Australian D-Health trial as simulated trials in UK Biobank data and reproduced the null results, but projected about 20–25% lower mortality in deficient people (hazard ratios 0.75–0.79).^[7] That projection rests on observational data, not on a trial, and a corrected genetic analysis found no such effect (see Vitamin D).

The secondary signals, and why they are weaker than they sound

Cancer deaths. Overall, cancer deaths were about 17% lower, a result compatible with no effect (hazard ratio 0.83, confidence interval 0.67–1.02). Leaving out the first two years, they were about a quarter lower (hazard ratio 0.75, confidence interval 0.59–0.96). That analysis was not in the trial protocol and was not adjusted for testing many outcomes at once, so it is best read as a hypothesis.^[8]

Advanced cancer. A later secondary analysis found advanced cancer, meaning cancer that had spread or was fatal, about 17% lower (hazard ratio 0.83, confidence interval 0.69–0.99). The clearest effect was in people of normal weight; none was detected in those with overweight or obesity.^[9]

Autoimmune disease. People taking vitamin D had about 22% fewer new autoimmune diagnoses over 5 years, a borderline result (hazard ratio 0.78).^[10] Once late-confirmed cases were added, the in-trial benefit shrank to about 15% and was no longer statistically clear (hazard ratio 0.85, confidence interval 0.70–1.04). Counting two more years after people stopped, there was no difference over the full 7 years (hazard ratio 0.98, confidence interval 0.83–1.17).^[11] Any protection seems to last only while you keep taking it, and may be smaller than first reported.

Telomeres. Telomeres are the protective caps on chromosomes that shorten as cells divide. In a four-year substudy of 1,031 participants, measured at the start, at year 2 and at year 4, those on vitamin D lost 0.14 kilobases less telomere than those on placebo, about 140 base pairs (confidence interval 0.007–0.27), a result only just past the usual threshold for statistical significance. Omega-3 had no effect on telomere length in the same trial.^[12] This is a real randomised finding, but from a single substudy, and on a surrogate marker: telomere length tracks real health outcomes only weakly. It is not a demonstrated gain in healthy years.

Inflammation. In 1,054 participants averaging about 65 years old, whose blood was tested at the start, at year 2 and at year 4, vitamin D lowered high-sensitivity C-reactive protein (hs-CRP), a blood marker of inflammation, by 19% at year 2 but not at year 4. The omega-3 capsules changed none of the inflammation markers measured.^[13] A short-lived dip in one marker is not evidence of slower ageing.

What VITAL can't tell you

• Whether deficient people benefit. Most participants already had enough, so a null result here is not evidence against correcting a real deficiency.
• Whether higher doses or higher targets help. Everyone in the active group took the same 2000 IU a day.
• Whether the secondary signals are real. Each one is a secondary, after-the-fact, substudy or borderline finding in a trial that tested many outcomes; none has been confirmed as a main result elsewhere.

What to do

1. Don't take vitamin D to prevent cancer, heart disease, fractures or depression if your level is already in range. VITAL is the strongest test of that idea, and it failed.
2. Do correct a real deficiency. VITAL says little about people who start low; see Vitamin D for the dose ladder.
3. If you take vitamin D, take it daily. VITAL dosed daily; large monthly or yearly doses did no better in other trials and may do harm, as in the D-Health trial.

Further reading

• Manson JE et al. Vitamin D Supplements and Prevention of Cancer and Cardiovascular Disease (VITAL). NEJM 2019.^[14]
• Chandler PD et al. Effect of Vitamin D3 Supplements on Development of Advanced Cancer: A Secondary Analysis of the VITAL Randomized Clinical Trial. JAMA Network Open 2020.^[15]
• Hahn J et al. Vitamin D and Marine Omega-3 Fatty Acid Supplementation and Incident Autoimmune Disease. BMJ 2022.^[16]
• Costenbader KH et al. Vitamin D and Marine n-3 Fatty Acids for Autoimmune Disease Prevention: Outcomes Two Years After Completion of a Double-Blind, Placebo-Controlled Trial. Arthritis & Rheumatology 2024.^[17]
• Zhu H et al. Vitamin D3 and marine ω-3 fatty acids supplementation and leukocyte telomere length: 4-year findings from the VITamin D and OmegA-3 TriaL (VITAL). Am J Clin Nutr 2025.^[18]
• LeBoff MS et al. Supplemental Vitamin D and Incident Fractures in Midlife and Older Adults. NEJM 2022.^[19]