Once thought of as only helping develop strong bones, vitamin D is now believed to serve many purposes in the human body. A deficiency of the vitamin has been linked to several diseases and disorders.
Yet most people don't get enough of the so-called "sunshine vitamin."
For years, Americans have been taught that as summer approaches, they should reach for sunscreen to protect themselves from a scorching burn - and the skin cancer it might trigger. But new research shows that by covering up, they may be sacrificing important vitamin D, which is made by the skin when it's exposed to sunlight.
So, ahead of the beach season, we sought some guidance about the "sunshine vitamin" from Dr. Elizabeth A. Streeten, assistant professor of medicine in the division of endocrinology, diabetes and nutrition at the University of Maryland School of Medicine. What does vitamin D do? New research seems to connect it with many aspects of good health besides good bones.
Vitamin D is important for the entire body. Vitamin D deficiency is associated with reduced bone strength and risk of fracture; a twofold increased risk of some cancers such as colon, breast and prostate; an increased risk of both Type 1 and Type II diabetes, worse control of diabetes for those who have it, decreased immune function and possibly also heart disease.
Vitamin D increases calcium absorption from the [gastrointestinal] tract and helps the bone become mineralized, or hardened. It also serves as a differentiating factor for cells, meaning that it helps to keep cells in their mature form and prevents them from mutating into cancer cells. Most vitamin D comes from sun exposure. How does that work, and how much sun is needed?
Ultraviolet B light contained in sunshine converts vitamin D precursors present in the skin to vitamin D. To become active, the body then converts vitamin D to 1,25-dihydroxyvitamin D, the only form that the body can use. This activation occurs via two-step process: the first in the liver and the second in the kidneys.
The truth on how much sun exposure is required is that we do not know exactly and there is significant variation among individuals. The recommendation is to get 15 minutes of sun at the peak of the day - 11 a.m. to 3 p.m. - to the face, neck and arms, three times a week. However, this amount of sun has not been proven to be enough.
