Vitamin D

Function

Vitamin D enables the intestines to absorb calcium and phosphorus, and supports immune regulation. Most is synthesized in skin from sunlight exposure rather than obtained from food, which is part of why deficiency is so widespread.

Food sources

Few whole foods are naturally rich in vitamin D (fatty fish, egg yolks); fortified foods (some orange juice, milk, cereal) are a major dietary source in the US.

Deficiency

See Vitamin D deficiency.

Relevant populations

Elderly — reduced skin synthesis and less sun exposure raise risk.

Citations

[1] NIH Office of Dietary Supplements — Vitamin D fact sheet.