Vitamin D

There are 2 forms of vitamin D that are important for human health: vitamins D2 and D3. Although these compounds are actually steroid hormones, they are grouped with the vitamins because they were misclassified back in 1922 and that misclassification has stuck. The major function of vitamin D for human health is to maintain normal blood levels of phosphorus and calcium and to aid in the absorption of calcium.

Vitamin D is produced by our bodies when our skin is exposed to the ultraviolet-B radiation of the sun. Most health experts recommend getting anywhere from 10 to 30 minutes of sunlight exposure per day without the use of sunblock in order to adequately supply the body with vitamin D. Since very few foods contain significant amounts of vitamin D, people who have limited access to sunlight run the risk of deficiency unless they take supplements or eat fortified foods.

Common symptoms of vitamin D deficiency include widespread bone pains, osteoporosis, muscle weakness, chronic fatigue, chronic pain, and depression. People most at risk include those who rarely go outside without sunblock or full coverings, those with dark skin pigmentation, children who are breastfeeding, and those suffering from intestinal problems such as Crohn's disease and celiac disease.

US Recommended Daily Allowance: 400 IU

Health Benefits of Vitamin D

Bones Aids in calcium absorption, helping to form and maintain strong bones. Recent research suggests it may help prevent osteoporosis. Deficiencies in children can cause rickets, which results in skeletal deformities.
Muscles A deficiency can cause muscular weakness. Scientific studies have found that vitamin D supplementation along with calcium supplementation of elderly women for three months increased muscle strength more than with calcium alone.