Vitamin D prevents cancer? The 25,871-person trial says no. And the 2024 guideline agrees
Vitamin D is one of the most taken supplements on earth. Two large pieces of evidence have now landed on the same conclusion: for most people, more vitamin D does not mean less cancer and less fractures.
- Claim
- VITAMIN D: PREVENTS CANCER?
- Catch
- NOT DEFICIENT
- Verdict
- SOME PEOPLE STILL NEED IT
The big trial: VITAL (VITamin D and OmegA-3 TriaL) is a two-by-two factorial, randomized, placebo-controlled trial in the United States. It randomized 25,871 men aged 50+ and women aged 55+ (50.6% women; 20.2% Black), giving them vitamin D3 2000 IU/day, marine omega-3 1 g/day, both, or placebo. The primary outcomes were invasive cancer and major cardiovascular events.
The finding: vitamin D was not associated with a lower risk of either. Invasive cancer: hazard ratio 0.96 (95% CI 0.88 to 1.06; P = 0.47) — 1617 cancers (793 vitamin D, 824 placebo). Major cardiovascular event: HR 0.97 (95% CI 0.85 to 1.12; P = 0.69). Among secondary outcomes, death from cancer was HR 0.83 (95% CI 0.67 to 1.02) — a hint, not a result, with the confidence interval crossing 1. A separate VITAL analysis published in NEJM in 2022 looked at fractures: 1991 confirmed fractures in 1551 participants over a median 5.3 years, and vitamin D3 did not reduce total fractures (HR 0.98, 95% CI 0.89 to 1.08; P = 0.70), nonvertebral fractures (HR 0.97) or hip fractures (HR 1.01). There was no modification of effect by age, sex, race, BMI, or baseline 25(OH)D level.
The catch — who these results do and don't apply to. VITAL participants were not selected for vitamin D deficiency, low bone mass, or osteoporosis. These are results about topping up people who mostly had enough. They say very little about someone who is genuinely deficient, and the paper is explicit that the effect did not vary with baseline serum 25(OH)D. Two things VITAL does not show: any cancer or cardiovascular benefit, and any fracture benefit. Note too that the trial used a fixed daily 2000 IU dose — the guideline separately advises against intermittent high-dose boluses, which have their own evidence base.
The catch — what the experts tell you to do. In 2024 the Endocrine Society published a clinical practice guideline, "Vitamin D for the Prevention of Disease" (Demay et al., JCEM 2024). Among its recommendations: the panel suggests against empiric vitamin D supplementation above the current Dietary Reference Intake to lower the risk of disease in healthy adults younger than 75 years, and suggests against routine 25(OH)D testing in all populations considered — no trial evidence was found to support routine screening in the general population, in people with obesity, or in people with dark complexion, and there was no clear evidence defining an optimal target level for disease prevention. The panel does suggest supplementation for children and adolescents aged 1–18, for adults aged 75 and older, in pregnancy, and for people with high-risk prediabetes. It also noted the optimal dose remains unclear because trial doses varied and many participants kept taking their own supplements.
SOURCES
- Manson JE, Cook NR, Lee IM, et al. "Vitamin D Supplements and Prevention of Cancer and Cardiovascular Disease." N Engl J Med. 2019;380(1):30–39. DOI: 10.1056/NEJMoa1809944. PMID 30415629. PMCID PMC6425757. ClinicalTrials.gov NCT01704859.
- LeBoff MS, Chou SH, Ratliff KA, et al. "Supplemental Vitamin D and Incident Fractures in Midlife and Older Adults." N Engl J Med. 2022;387(3):203–213. DOI: 10.1056/NEJMoa2202106. PMID 35939577.
- Demay M, Pittas A, Bikle D, et al. "Vitamin D for the Prevention of Disease: An Endocrine Society Clinical Practice Guideline." J Clin Endocrinol Metab. 2024;109(8):1907–1947. DOI: 10.1210/clinem/dgae290. PMID 38828931. (Corrections: DOI 10.1210/clinem/dgae854; DOI 10.1210/clinem/dgaf310.)
Disclaimer: For information only, not medical advice. Vitamin D is important for people who are deficient, for bone health, and for a number of specific conditions — this short is about whether extra vitamin D prevents cancer and fractures in people who already have enough. If you are considering high doses, taking it alongside other medicines, or have a condition that affects vitamin D, talk to your doctor.
