According to many experts, 10–15 minutes of sun (ultraviolet-B radiation) exposure on arms and legs or face and arms three times weekly between 10:00 a.m. and 3:00 p.m. during the spring, summer, and fall at 40 degrees latitude should provide a light-skinned individual with adequate vitamin D3, produced in the skin(87). One study reported that vitamin D concentrations in blood following exposure to 1 minimal dose of simulated sunlight, causing a slight pinkness of the skin, was equivalent to ingesting approximately 20,000 IU of vitamin D2 (90).
However, in latitudes around 40 degrees north or 40 degrees south, there is insufficient sun UVB radiation available for vitamin D synthesis from November to early March. Ten degrees farther north or south this period extends from mid-October to mid-March.
People with dark-colored skin synthesize markedly less vitamin D on exposure to sunlight than those with light-colored skin (1). Additionally, the elderly have diminished capacity to synthesize vitamin D from sunlight exposure and block vitamin D3 synthesis by frequently using sunscreen or wearing protective clothes.
Vitamin D is found naturally in very few foods, including some fatty fish (mackerel, salmon, and sardines), fish liver oils, and eggs from hens that have been fed vitamin D. In some countries, milk and infant formula are fortified with vitamin D.
Vitamin D supplements are a reliable source of vitamin D especially during wintertime when there is almost no vitamin D production in the skin. Most vitamin D supplements available without a prescription contain vitamin D3 (cholecalciferol), generally providing 400 IU (10 mcg) of vitamin D. A number of calcium supplements may also provide vitamin D.
Authored by Dr Peter Engel in 2010, reviewed and updated by Dr Igor Bendik-Falconnier on 18.06.2017
