Vitamin D

Vitamin D is a fat-soluble vitamin that the skin synthesizes from sunlight (UVB) and that is also obtained from foods (fatty fish, egg yolk, fortified milk and cereals) and supplements. Its central role is enabling calcium and phosphorus absorption for bone mineralization (see calcium); it also supports muscle function and immune health. Severe deficiency causes rickets in children and osteomalacia in adults, and low status contributes to bone loss and fracture risk.

Recommended intake (Institute of Medicine): 600 IU/day (15 mcg) for ages 1–70, rising to 800 IU/day (20 mcg) after age 70. The tolerable upper intake level for adults is 4,000 IU/day.

Vitamin D is one of the most common shortfalls because sun exposure is often limited (latitude, indoor lifestyles, sunscreen, darker skin pigmentation reduces synthesis) and few foods are naturally rich in it. At-risk groups include older adults (see senior-training), people with little sun exposure, those with darker skin, and people with malabsorption. Status is checked with a serum 25-hydroxyvitamin D test; supplementation (commonly D3) is the standard correction when blood levels are low.

• Fat-soluble; made in skin from UVB sunlight; few rich food sources.
• Enables calcium/phosphorus absorption for bone; aids muscle and immunity.
• RDA 600 IU (15 mcg) ages 1–70; 800 IU (20 mcg) after 70; UL 4,000 IU/day adults.
• One of the most prevalent deficiencies; at-risk: older adults, low sun, darker skin, malabsorption.
• Confirmed by serum 25(OH)D; supplement D3 to correct low status.

• calcium — vitamin D drives calcium absorption.
• vitamins-overview — a fat-soluble vitamin.
• senior-training — older adults need more and absorb less.
• bone-tissue — bone mineralization depends on vitamin D.