Vitamin D, also known as calciferol, is a fat-soluble vitamin that is naturally present in very few foods, added to others, and available as a dietary supplement.
Vitamin D also can be made in your body after exposure to ultraviolet rays from sunlight that strike the skin and trigger vitamin D synthesis.
The vitamin exists in the body in several forms.
There are two main types of vitamin D: Vitamin D2 and Vitamin D3. Both forms of vitamin D have been used successfully to treat rickets and other diseases related to vitamin D insufficiency.
Vitamin D2 is formed by the action of UV-B on the plant precursor ergosterol. It is found in plants.
Vitamin D3 or cholecalciferol is found in animal foods. Most milk today contains D3.
Vitamin D3 is often thought to be the preferred vitamin because it has more biological activity. Since it is found in food and in human skin, it always has various metabolites or isomers that may have biological benefit.
There may be as many as 12 metabolites or isomers in the vitamin D found in animal foods. When vitamin D is taken in the form of fish oil, or eaten in foods such as eggs or fish, these metabolites will be present.
Vitamin D obtained from sun exposure, food, and supplements is biologically inert and must undergo two hydroxylations in the body for activation.
- The first occurs in the liver and converts vitamin D to 25-hydroxyvitamin D [25(OH)D], also known as calcidiol.
- The second occurs primarily in the kidney and forms the physiologically active 1,25-dihydroxyvitamin D [1,25(OH)2D], also known as calcitriol.
Vitamin D is essential for promoting calcium absorption in the gut. Calcium in turn offer some health benefits that we cannot ignore:
- • Calcium aids in fat loss and maintaining proper weight
- • Calcium helps regulate the heart beat
- • Calcium helps in blood clotting and fat digestion
- • Calcium helps regulate blood pressure
That way Vitamin D is essential in maintaining adequate serum calcium and phosphate concentrations in the body to enable normal mineralization of bone and prevent hypocalcemic tetany.
It is also needed for bone growth and bone remodeling by osteoblasts and osteoclasts. Without sufficient vitamin D, bones can become thin, brittle, or misshapen.
A growing body of research suggests that vitamin D might play some role in the prevention and treatment of type 1 and type 2 diabetes, and it plays an essential role in lowering high blood pressure or hypertension.