Vitamin D3
Vitamin D3, or cholecalciferol, is one form of the fat-soluble vitamin D. Skin makes it in response to UV light, and it also comes from foods and supplements.
Also listed as Cholecalciferol, Vitamin D, D3, Vitamin D-3
Does D3 prevent fractures in everyone?
Deficiency-related bone disease and routine fracture prevention are different questions. In VITAL, 25,871 generally healthy middle-aged and older adults received 50 µg (2,000 IU) D3 daily or placebo for a median 5.3 years; fractures were not reduced. Most participants were already vitamin D sufficient, so this result does not negate treatment of deficiency. 1
When does calcium change the evidence?
Vitamin D plus calcium can produce small gains in bone density and reduce fractures in institutionalized older adults. Results in people living independently are inconsistent. A combination finding should not be presented as proof that D3 alone improves bone density or prevents fractures across all groups. 1
Can vitamin D prevent respiratory infections?
A 2025 updated meta-analysis found no statistically significant overall reduction: odds ratio 0.94 (1 means no difference), with a 95% confidence interval of 0.88–1.00, across 40 placebo comparisons involving 61,589 participants. The estimate still allowed a modest benefit, but subgroup analyses did not establish differences by baseline status, age or dosing. This is uncertainty about the size of prevention benefit, not evidence that vitamin D has no immune function. 1 2
The updated pooled estimate did not establish protection; a modest benefit remained compatible with the interval. 2
Are there groups for whom prevention guidance differs?
The 2024 Endocrine Society guideline suggests supplementation alongside lifestyle changes for high-risk prediabetes. It also supports empiric supplementation during pregnancy and from age 75, with differing certainty. For generally healthy adults under 75, it advises against routine doses above dietary reference intakes. These are group-specific recommendations, not a universal high-dose regimen. 3
Does D3 improve mood?
Low vitamin D status and depression are associated in observational studies, and vitamin D receptors in the brain provide a biological hypothesis. In the large VITAL depression study, 2,000 IU D3 daily did not reduce depression or improve mood scores over a median 5.3 years in middle-aged and older adults. That prevention result does not settle every treatment question in patients with diagnosed depression and deficiency. 1
Why distinguish cancer incidence from mortality?
Trials have generally not shown that supplementation prevents new cancer diagnoses. Some trial meta-analyses summarized by NIH found lower cancer mortality, a different endpoint. This signal warrants investigation but is not evidence that D3 treats cancer or that high doses improve outcomes for an individual patient. 1
Effects by health goal
Open an effect to see the studies behind its rating. Bars show the size of the effect; the letter grades the evidence.
Essential Health1 effect
Immune Support2 effects
Bone & Joint2 effects
No study is linked to this rating.
Stress & Mood2 effects
Fertility1 effect
No study is linked to this rating.
Women's Hormones1 effect
No study is linked to this rating.
Longevity1 effect
Fitness1 effect
Cardiovascular2 effects
No study is linked to this rating.
No study is linked to this rating.
Cognition1 effect
Hair & Skin1 effect
No study is linked to this rating.
Weight Management1 effect
No study is linked to this rating.
Other effects1 effect
All studies
21 publications are linked to Vitamin D3, newest first.
Sources
- Vitamin D: Fact Sheet for Health Professionals NIH Office of Dietary Supplements
- Vitamin D for the Prevention of Disease Endocrine Society, 2024