Vitamin D refers to a group of fat-soluble nutrients responsible for enhancing intestinal absorption of calcium, iron, magnesium, phosphate and zinc.
In humans, the most important compounds in this group are vitamin D3 and vitamin D2. They can be ingested from the diet and from supplements. Few foods contain vitamin D in the skin is the major natural source of the vitamin. Dermal synthesis of vitamin D from cholesterol is dependent on sun exposure.
Dietary Reference Intake for vitamin D assumes no synthesis occurs and all of a person's vitamin D is from food intake, although that will rarely occur in practice. But the DRI is so low because it was developed to prevent rickets, not to optimize health.
Vitamin D has a significant role in calcium homeostasis and metabolism. There is growing evidence that vitamin D may reduce the risk of a variety of health concerns.
Vitamin D is very important for bone health. It helps build stronger bones, partly by increasing the absorption of calcium. Vitamin D also improves the function of muscles, which in turn improves your balance and decreases the likelihood of falling.
Healthy adults between 19-50 years of age, including pregnant or breast-feeding women, require a minimum of 400 to 1,000 IU daily.
In the last several years, there has been a flood of health news about studies linking vitamin D deficiency with neoplasms, cardiovascular diseases, diabetes, metabolic disorders, depression, infectious diseases, autoimmune diseases, mortality and even autism.
A search on PubMed for vitamin D finds many hundreds of academic papers.
John J. Cannell, MD, Founder and Executive Director of the Vitamin D Council, says, “Many people are turned off by these claims and say it’s impossible that one thing is involved in so many different disease processes, but they are unaware of the mechanism of vitamin D. It is actually a steroid hormone precursor that turns genes on and off. There are at least a thousand genes that are directly regulated by vitamin D.”