Vitamin D

Vitamin D, also called calciferol, is a fat-soluble vitamin that the body needs to absorb calcium and to build and maintain bones. It is naturally present in a few foods, added to others and sold as a supplement, and the body also makes it when ultraviolet rays from sunlight strike the skin.

Forms and sources

In foods and supplements vitamin D has two main forms, D2 (ergocalciferol) and D3 (cholecalciferol), which differ only in their side chain and are both well absorbed in the small intestine. Few foods contain it naturally: the flesh of fatty fish such as trout, salmon, tuna and mackerel and fish liver oils are among the best sources, and beef liver, egg yolks and cheese have small amounts.

In the body

Vitamin D promotes calcium absorption in the gut and keeps calcium and phosphate in the blood at the levels needed for normal bone mineralisation; it is also needed for bone growth and bone remodelling.

How much

In the United States, the recommended intakes are 15 to 20 µg (600 to 800 international units, IU) a day for adults and 10 to 15 µg (400 to 600 IU) for infants, children and adolescents, depending on age.

Too much

Vitamin D toxicity, almost always the result of too many supplements, can cause high blood calcium and, in extreme cases, kidney failure, calcification of soft tissues, heart rhythm disorders and death.

Products containing it

• All Day Fit A-Z Compact tablets (S 06)
• Eye Care Capsules (D 242)
• Viva K2 capsules (D 224)