Vitamin D3

Established Supplementsrecovery Last reviewed 2026-09-24

Summary

An essential fat-soluble vitamin with established roles in calcium handling and bone health. Correcting deficiency is strongly supported; benefits for other outcomes in non-deficient people are not supported by large trials.

Mechanism

Vitamin D3 (cholecalciferol) is hydroxylated in the liver to 25(OH)D — the blood marker of status — and in the kidney to calcitriol, which binds the vitamin D receptor to regulate calcium and phosphate absorption and bone mineralization. It also modulates innate immune function, including antimicrobial peptide production.

Reported effects

Ratings are relative to peers in the same category, not absolute claims.

Bone health / correcting deficiency★★★★★Correcting deficiency prevents rickets and osteomalacia; the strongest-supported use.

Respiratory infection risk★★☆☆☆Benefit concentrated in deficient individuals; absent with infrequent bolus dosing.

Cardiovascular disease / cancer prevention (general population)★☆☆☆☆The large VITAL trial found no reduction in major CV events or invasive cancer.

Studied dosing — research context

Most trials use 1000-4000 IU/day; the Endocrine Society guideline suggests 1500-2000 IU/day for adults to maintain 25(OH)D above 30 ng/mL; the VITAL trial used 2000 IU/day for a median of 5.3 years. These are doses used in research, not guidance.

Research context only. This is not a recommendation.

Safety

Safe at typical studied doses. Toxicity (hypercalcemia) is rare and associated with very high doses.

Limitations

Much of the disease-association evidence is observational and vulnerable to reverse causality — VITAL's null results illustrate the gap between association and supplementation benefit. Benefits appear largely confined to deficient individuals, and debate continues over the optimal blood level.