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Vitamin

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

Essential HealthImmune SupportBone & JointStress & MoodFertility

What it is studied for

The strongest rated effects first. Bars show the size of the effect, the letter grades the evidence, and each rating lists the studies behind it.

Essential HealthStrongA3 studies
Immune SupportModerateA3 studies
Bone densityBone & JointModerateA3 studies
Immune responseImmune SupportModerateA3 studies
InflammationModerateA3 studies
Mood SupportStress & MoodModerateB2 studies
All 17 rated effectsGrouped by health goal, with the publications behind each rating

What is vitamin D3?

Vitamin D3, or cholecalciferol, is one form of the fat-soluble vitamin D. Skin produces it in response to ultraviolet light, and it is also obtained from foods and supplements. The liver converts vitamin D to 25-hydroxyvitamin D, the main blood marker of status; further activation occurs mainly in the kidneys. 1

What is its established job?

Vitamin D supports calcium absorption and normal bone mineralization. Adequate status prevents rickets in children and osteomalacia, or poorly mineralized bone, in adults. Its roles in immune signaling and cell regulation explain broader research interest, but do not establish that extra D3 prevents every associated disease. 1

Key studies

The most recent publications linked to Vitamin D3's ratings.

Effects of Vitamin D on Cardiovascular Risk and Oxidative Stress2023Measurements of the Vitamin D Metabolome in the Calgary Vitamin D Study: Relationship of Vitamin D Metabolites to Bone Loss2023The effect of vitamin D supplementation on the brain mapping and behavioral performance of children with ADHD: a double-blinded randomized controlled trials2023Effect of supplemental vitamin D3 on bone mineral density: a systematic review and meta-analysis.2022The Effects of Vitamin D on Immune System and Inflammatory Diseases2021
All 21 studiesEvery publication linked to Vitamin D3

Why people take it

Essential Health21.8%
Immune Support20.1%
Bone & Joint15%
Energy12.2%
Longevity6%
Cognition5%

SuppCo community snapshot, 2026-09-28. Reasons for use are not evidence that it works.

Questions people ask

Is D3 the same as vitamin D?

D3 is cholecalciferol, one form of vitamin D; D2 is another. 1

Is 20 µg the same as 800 IU?

Yes. DGE uses the conversion 1 µg vitamin D equals 40 IU. 2

Does a higher blood level mean better health?

Not automatically. D3 raises the status marker, but trials in generally sufficient adults have not consistently shown additional health benefits. 1

Can I get D3 without animal ingredients?

Yes, lichen-derived D3 exists; many other D3 products use lanolin. 1

Does sunlight make supplements unnecessary?

Skin synthesis contributes to status, but varies with factors including season and skin exposure. NIH also emphasizes protection from UV damage rather than unrestricted sun exposure. 1

Sources

  1. Vitamin D: Fact Sheet for Health Professionals NIH Office of Dietary Supplements
  2. Vitamin D: Referenzwerte Deutsche Gesellschaft für Ernährung