The recommended daily allowance of vitamin D for children age 1 and under is 400 international units, while the recommendation for children ages 1 to 70 is 600 international units. The recommended daily allowance is sufficient to meet the needs of nearly all healthy people.
Vitamin D is essential to good health because it aids in the absorption of calcium, which is important for healthy bones. When combined in sufficient amounts with calcium, vitamin D also helps prevent rickets in children and osteoporosis in older adults. Vitamin D plays also plays a role in cell growth, neurological, muscular and immune function, and reducing systemic inflammation.
Vitamin D does not occur naturally in very many foods. The best sources of vitamin D are the flesh of fatty fish and fish liver oils, and small amounts the vitamin are present in beef liver, cheese and egg yolks. Many foods are fortified with vitamin D, and it is widely available in supplement form. In fact, most of the vitamin D present in the American diet comes from fortified foods.
The human body naturally produces vitamin D as a result of the skin's exposure to ultraviolet radiation from sunlight, which triggers vitamin D synthesis.