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

Those cancers include basal-cell carcinomas and squamous-cell carcinomas, two common types of non-melanoma skin cancers that aren't usually life-threatening, the study says. People who have ever used indoor tanning are 29% more likely to develop basal-cell carcinomas than those who have never used tanning salons, it adds.

Indoor tanners are 67% more likely to develop the more serious squamous-cell carcinomas compared with those who have never tanned indoors, says Eleni Linos, an assistant professor of dermatology at the University of California-San Francisco and senior author of the study.

That suggests indoor tanning is responsible for about 5% of non-melanoma skin cancers, the most commonly diagnosed cancers in the USA, says Thomas Glynn, director of cancer science and trends at the American Cancer Society. Non-melanoma skin cancers strike about one in five Americans during their lifetime, including 30% of whites, Linos says. Those who started tanning indoors before age 25 had the highest skin cancer risk, according to the analysis, which included 12 studies involving 80,000 people in six countries.

Other research has linked indoor tanning to malignant melanoma, the deadliest type of skin cancer, Linos says. The International Agency for Research on Cancer, part of the World Health Organization, has classified ultraviolet radiation from tanning beds as a Class 1 carcinogen, the same category as tobacco smoke and asbestos. Linos says the study lends support to state and city efforts to ban children and teens from tanning salons.

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

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

A number of scientists are studying the role of vitamin D in preventing health problems such as heart attacks and strokes, although these studies involve providing vitamin D supplementation through pills, not UV exposure.

"UV exposure, 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, while the benefits remain unnoticed and unpromoted."

USA Today