What are the best ways to achieve adequate vitamin D intake?
There are two natural forms of vitamin D—cholecalciferol (D3) and ergocalciferol (D2). Fatty fish (salmon, tuna, mackerel; D3 = 400 IU/3.5oz), fortified milk (400 IU/quart), and cereal products (50 IU/cup) are good dietary sources. Vitamin D2 and D3 supplements are available over the counter in multiple doses and 50,000 IU vitamin D2 supplements can be given by prescription. Ten minutes of midday summer sunlight exposure to a fair-skinned person in a tank-top and shorts not wearing sunscreen produces 10,000 IU of vitamin D3. Dark-skinned individuals and the elderly get less production. However, many individuals wear sunscreen (sun protection factor >8), which prevents vitamin D production by the skin. Therefore, oral vitamin D is necessary for most people. The optimal vitamin D intake is 800 to 1200 IU daily and should not exceed 4000 IU/day chronically.