Vitamin D
A hormone-like vitamin made in skin from sunlight, central to bone health and immune function.
Recommended intake
600–800 IU/day for most adults; many clinicians target higher blood levels via supplementation, especially in winter or low-sun climates.
Upper limit
4,000 IU/day for most adults without medical supervision.
Deficiency signs
- • Fatigue
- • Bone pain
- • Frequent infections
- • Low mood
Food sources
- • Oily fish
- • Egg yolks
- • Fortified dairy or plant milks
- • Sunlight exposure
Evidence note
Strong evidence for bone health and immune function; supplementation is well-supported in people with low blood levels.