At least 170,000 cases of skin cancer each year are linked to indoortanning, according to an analysis published online Tuesday in theBritish medical journal BMJ.

Those cancers includebasal-cell carcinomas and squamous-cell carcinomas, two common types ofnon-melanoma skin cancers that aren't usually life-threatening, thestudy says. People who have ever used indoor tanning are 29% more likelyto develop basal-cell carcinomas than those who have never used tanningsalons, it adds.

Indoor tanners are 67% more likely to developthe more serious squamous-cell carcinomas compared with those who havenever tanned indoors, says Eleni Linos, an assistant professor ofdermatology at the University of California-San Francisco and seniorauthor of the study.

That suggests indoor tanning is responsiblefor about 5% of non-melanoma skin cancers, the most commonly diagnosedcancers in the USA, says Thomas Glynn, director of cancer science andtrends at the American Cancer Society. Non-melanoma skin cancers strikeabout one in five Americans during their lifetime, including 30% ofwhites, Linos says. Those who started tanning indoors before age 25 hadthe highest skin cancer risk, according to the analysis, which included12 studies involving 80,000 people in six countries.

Otherresearch has linked indoor tanning to malignant melanoma, the deadliesttype of skin cancer, Linos says. The International Agency for Researchon Cancer, part of the World Health Organization, has classifiedultraviolet radiation from tanning beds as a Class 1 carcinogen, thesame category as tobacco smoke and asbestos. Linos says the study lendssupport to state and city efforts to ban children and teens from tanningsalons.

Last year, California became the first state in thecountry to ban tanning by minors. Brazil has gone even further bybanning indoor tanning entirely, Linos says.

John Overstreet,executive director of the Indoor Tanning Association, says consumersshould be free to make informed choices about the benefits and risks ofindoor tanning. He cites research suggesting that ultraviolet radiationfrom tanning beds provides vitamin D.

A number of scientists arestudying the role of vitamin D in preventing health problems such asheart attacks and strokes, although these studies involve providingvitamin D supplementation through pills, not UV exposure.

"UVexposure, whether from the sun or a sunbed, has many benefits,"Overstreet says. "As with most human activities, there are also risks.It seems the risks continue to grab the headlines in the media, whilethe benefits remain unnoticed and unpromoted."