Vitamin D3

Vitamin D3 (cholecalciferol) is a natural form of vitamin D that is synthesized in the skin in response to exposure to ultraviolet rays from the sun. This fat-soluble vitamin has properties of both a vitamin and hormone, and is required in calcium absorption and utilization.*
 
For children, vitamin D is especially important for growth, the normal development of bones and teeth, and immune health. Vitamin D also protects against muscle weakness, is involved in regulation of the heart beat, and is necessary for healthy thyroid function, normal blood clotting and healthy arteries.*

Vitamin D3 is substantially more effective than vitamin D2 (ergocalciferol), which comes from food sources.

While regularly exposing the skin to sunlight is an effective way to get vitamin D, researchers have found that those who live in northern latitudes, spend a lot of time indoors, wear sunscreen, have darker skin or have a chronic health condition may not get adequate vitamin D.

Research has shown that low vitamin D levels are associated with serious and chroic health conditions and that most Americans are deficient in vitamin D. Doctors are recommending that the U.S. Institutes of Medicine raise it recommended daily intake.