People who try to stay bronze with the help of a tanning bed tend to have higher blood levels of vitamin D than those shun the salon, according to a new study.

The findings, say the study authors, suggest that a regular appointment at the tanning salon may have health benefits -- though they and other experts don't recommend that people start tanning in order to boost their vitamin D levels.

The study of 156 adults found those who regularly soaked up the artificial rays of a tanning bed had a 90 percent higher average vitamin D concentration in their blood. The tanners, who frequented the salon at least once a week for 6 or more months, also had greater bone density in the hips.

The study, published in the American Journal of Clinical Nutrition, was partially financed by the UV Foundation, which is funded by the Indoor Tanning Association, an industry group.

A precursor to vitamin D exists naturally in the skin, and exposure to the sun's ultraviolet (UV) rays touches off a chemical process that creates the usable form of the vitamin. Because vitamin D is needed for proper calcium absorption, the nutrient is vital to bone health. There is also a body of research suggesting vitamin D helps protect against certain cancers and some autoimmune diseases, such as type 1 diabetes and multiple sclerosis.

But the fact that UV radiation is the major cause of skin cancer, as well as the major source of vitamin D, has made for a controversy over how much sun -- or artificial sun -- people should get.

The senior author on the new study, Dr. Michael F. Holick of Boston University School of Medicine, has for some time advocated that people spend a short amount of time outside, without sunscreen, several days a week -- with the amount of time depending on factors such as latitude and a person's skin sensitivity.

For a white person in Boston, that might mean 10 minutes in the sun, while a darker-skinned person would need longer exposure.

"I'm not an advocate of tanning," Holick stated in an interview, noting that some people -- those with particularly sun-sensitive skin that never tans -- should avoid tanning salons.

However, Holick said, the new findings indicate that there is a "health benefit above and beyond feeling good" from tanning beds that emit UVB light, the form of UV radiation that triggers vitamin D production.

Moreover, Holick said, the results add to research showing that many Americans may be low in vitamin D. A number of studies have found fairly high rates of vitamin D deficiency in the U.S., particularly among African Americans, who need more UV exposure to produce the vitamin.

Among the 50 tanning-salon patrons in Holick's study, 8 percent were deemed deficient in vitamin D, compared with 41.5 percent of non-tanners.

But dermatologists, concerned about skin cancer, balk at the idea that many Americans need to increase their UV exposure for the sake of vitamin D.

The American Academy of Dermatology advises people to avoid outdoor activities when the sun's rays are strongest -- between 10 a.m. and 4 p.m. -- and to wear sunscreen with SPF 15 or higher whenever they're outside. The group has also urged a ban on the use of tanning equipment for non-medical purposes.

"You get plenty of UV light in your normal daily activities," said Dr. Darrell S. Rigel, a clinical professor of dermatology at New York University in New York City.

Even when protected with sunscreen, he noted in an interview, the skin still absorbs UV rays and churns out vitamin D.

Anyone concerned about getting enough of the nutrient, Rigel said, can get more by taking vitamin supplements and from vitamin D-fortified milk or other dietary sources of the vitamin. Some cereals and juices are also D-fortified, and fatty fish such as salmon and tuna are natural sources.

With UV radiation known to be a carcinogen, Rigel said, "there's no reason to go to a tanning bed."

Holick said that people who do not wish to get more sun should take supplements to increase their vitamin D levels, as it may be tough to consume enough milk and fatty fish.

SOURCE: American Journal of Clinical Nutrition, December 2004.