For those who do not obtain adequate amounts of vitamin D, from either their diet or exposure to sunlight, vitamin D supplements taken orally are an option.
As supplements, D2 and D3 are the most common. D2 (ergocalciferol) is synthetic. D3 (cholecalciferol) is the better choice if you want a natural form of vitamin D. It is the type the human body synthesizes from sunlight.
Recommended intake for children and adults, who are in good health, is a minimum of 600 IU of vitamin D per day. Many people think 1000-4000 IU of vitamin D should be the recommended daily supplement intake amount for adults.