Vitamin D

Vitamin D, calciferol, is a fat-soluble vitamin. Vitamin D exists in several forms, each with a different activity. The liver and kidney help convert vitamin D to its active hormone form.
What does Vitamin D do?
Vitamin D aids in the absorption of calcium, helping to form and maintain strong bones. Without vitamin D, bones can become thin, brittle, soft, or misshapen.
What are the sources of Vitamin D?
One cup of vitamin D fortified milk supplies about one-fourth of the estimated daily need for this vitamin for adults. The list below includes selected food sources of vitamin D.
• Exposure to sunlight
Exposure to sunlight is an important source of vitamin D. Ultraviolet (UV) rays from sunlight trigger vitamin D synthesis in the skin.
How much vitamin D do we need?
Ages 51-69: 400 IU
When can vitamin D deficiency occur?
A deficiency of vitamin D can occur when dietary intake of vitamin D is inadequate, when there is limited exposure to sunlight, when the kidney cannot convert vitamin D to its active form, or when someone cannot adequately absorb vitamin D from the gastrointestinal tract.
The classic vitamin D deficiency diseases are rickets and osteomalacia. In children, vitamin D deficiency causes rickets, which results in skeletal deformities.
Who may need extra vitamin D to prevent a deficiency?
Vitamin D supplements are often recommended for exclusively breast-fed infants because human milk may not contain adequate vitamin D. Since infant formulas are routinely fortified with vitamin D, formula fed infants usually have adequate dietary intake of vitamin D.
Current Issues and Controversies About Vitamin D
A greater vitamin D intake from diet and supplements has been associated with less bone loss in older women. Since bone loss increases the risk of fractures, vitamin D supplementation may help prevent fractures resulting from osteoporosis.
Treatment of vitamin D deficiency can result in decreased incidence of hip fractures, and daily supplementation with 800 IU (20 micrograms) of vitamin D may reduce the risk of osteoporotic fractures in elderly populations with low blood levels of vitamin D.
• Vitamin D and cancer:Laboratory, animal, and epidemiologic evidence suggest that vitamin D may be protective against some cancers. Well-designed clinical trials need to be conducted to determine whether vitamin D deficiency increases cancer risk, or if an increased intake of vitamin D is protective against some cancers. Vitamin D and Alzheimer's Disease: Adults with Alzheimer's disease have increased risk of hip fractures.
What is the health risk of too much vitamin D?