Come and get your sun: Covering up deprives your body of vitamin D

New research shows slathering on sunscreen can prevent, in addition to sunburn, the body's natural and needed production of vitamin D. So as summer approaches, here's advice on avoiding a deficiency of the vitamin and the diseases and disorders that can lead to:

Q What does vitamin D do? New research seems to connect it with many aspects of good health besides good bones.

A 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 2 diabetes. Vitamin D increases calcium absorption from the (gastrointestinal) tract and helps the bone become mineralized, or hardened. It also helps to keep cells in their mature form and prevents them from mutating into cancer cells.

Q Most vitamin D comes from sun exposure. How does that work, and how much sun is needed?

A Ultraviolet B light contained in sunshine converts vitamin D precursors 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 a 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. Also, more sun is needed to make vitamin D with increasing age and increasing amounts of skin pigment.

Q How many people are deficient? Is it a growing problem or just a constant problem since there has been so much focus on sunscreen and not enough focus on diet?

A Up to 65 percent of Americans are vitamin D-deficient, with the highest levels in the elderly. However, studies have shown that up to half of young adults and children are also deficient.

We do not know if the prevalence of vitamin D deficiency is growing or not, since the accurate blood test to detect it is fairly new. There is not enough vitamin D in foods for our needs. There is substantial vitamin D only in some fish, such as salmon, swordfish, tuna, sardines, and only tiny amounts in other foods. ... Therefore, to get enough vitamin D for our needs -- 1,000 to 2,000 units daily for adolescents and adults -- everyone should take a vitamin D supplement, at least during September through May.

Q If sunscreen with SPF 8 and over blocks the skin's ability to make vitamin D, should people just wear lower SPF lotion and reapply frequently? Does UVA or UVB protection make a difference?

A UVB rays are what is needed for vitamin D production, whereas both UVA and UVB can cause sunburn and tan. One way to prevent sunburn and allow vitamin D synthesis is to put on sunscreen only after being in the sun for 15 minutes.

Q What about skin cancer? Is there a risk from being in the sun even for a limited time or using lower SPF sunscreen?

A There is no data available to show that small amounts of skin sun exposure -- 15 minutes before applying sunscreen -- increase the risk of skin cancer. Exceptions to this may be redheads and others with extremely fair skin who burn easily.

BALTIMORE SUN