For years, Americans have been taught that they should use 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, we sought some guidance from Elizabeth A. Streeten, assistant professor of medicine at the University of Maryland School of Medicine.

Question: What does Vitamin D do?

Answer: 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 diabetes; and possibly also heart disease.

Q: Most Vitamin D comes from sun exposure. How much sun is needed?

A: Ultraviolet B light in sunshine converts Vitamin D precursors in the skin to Vitamin D. 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 has not been proven to be enough . . .

Q: How many people are deficient?

A: Up to 65 percent of Americans are Vitamin D deficient, with the highest levels in the elderly. Studies show that up to half of young adults and children are also deficient.

There is not enough Vitamin D in foods for our needs. For the average adult to get enough Vitamin D from milk, he or she would have to drink eight cups of milk per day.

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: What about skin cancer?

A: There is no data available to show that small amounts of skin sun exposure - 15 minutes before applying sunscreen - increases the risk of skin cancer.