by Michael Smith

Indoor tanning is associated with a 74% higher risk of melanoma, researchers said.

And, in a large case-control study, some forms of indoor tanning machines were associated with a four-fold increase in the risk of skin cancer, according to DeAnn Lazovich, PhD, of the University of Minnesota, and colleagues.

The risk rose in a dose-response fashion depending on years of use, hours of use, or number of sessions, Lazovich and colleagues said online in Cancer Epidemiology, Biomarkers & Prevention.

The finding “provides strong support” for a recent declaration by the World Health Organization’s cancer research agency that the devices are carcinogenic, the researchers concluded.

“The take-home message is that indoor tanning is not safe,” Lazovich said in a video prepared by the University of Minnesota.

Tanning salons are increasingly popular in the U.S. and their rise has been paralleled by increasing incidence of melanoma, the researchers noted.

But evidence that might show a link has been inconclusive, they said, largely because studies of the issue have not accounted for confounders such as sun exposure or measured dose response. Nevertheless, the International Agency for Research on Cancer reported a summary odds ratio of 1.15, based on 19 studies, they said.

To help fill the gaps, Lazovich and colleagues undertook a case-control study in Minnesota, where there is a high prevalence of indoor tanning. Cases were 1,167 people ages 25 through 59 who were diagnosed with invasive cutaneous melanoma between July, 2004, and December, 2007. The 1,101 controls were age and sex-matched to the cases on a one-to-one basis.

Participants took a self-administered questionnaire, followed by a detailed one-hour telephone interview. The data collected included such things as the age when indoor tanning started, its intensity in terms of duration and time of use, and the types of machines used, as well as sun exposure and a range of risk factors for melanoma.

Overall, 62.9% of cases reported using tanning machines, compared with 51.1% of the controls. In a multivariate model adjusted for all of the available confounding factors, the odds ratio for a melanoma patient having used a tanning machine was 1.74, with a 95% confidence interval from 1.42 to 2.14.

Four types of machines were used — conventional, high-pressure, high-speed and intensity, and sun lamps. The researchers found that cases were significantly more likely than controls to have used any type of machine, but the odds ratios ranged from 1.76 for conventional devices to 4.44 for so-called high-pressure devices, which primarily emit ultraviolet A light.

The risk of melanoma also increased with use, regardless of how it was measured. Specifically, compared with those who had ever used the devices:

* People who had used an indoor tanning machine for between one and nine hours in total had a significant odds ratio for melanoma of 1.46, compared with 3.18 for those with more than 50 hours of use. The trend was significant at P<0.0001.
* Those who had 10 or fewer sessions had a significant odds ratio for melanoma of 1.34, compared with 2.72 for those with more than 100 sessions. The trend was significant at P=0.0002.
* Those who had used the devices for a year or less had a significant odds ratio for melanoma of 1.46, compared with 2.45 for those who had used the machines for 10 or more years. The trend was significant at P<0.006.

Over time, different types of machines, with differing frequency characteristics, have been used. However, the risk of disease was significantly elevated for use before 1990 and after, as well as for both periods together, the researchers found.

They cautioned that the study is unable to determine which form of ultraviolet light — A or B — is responsible for the results.

But the results were challenged by the International Smart Tan Network, which describes itself as “the educational institute for the North American indoor tanning community.”

In a news release, the organization’s vice-president, Joseph Levy, said Lazovich is “an advocate, not a neutral party, and the advocate failed to properly disclose that she is not a neutral party.”

Levy said Lazovich is a member of a group at the University of Minnesota that “initiated programs to discourage indoor tanning use three years before designing and engaging in data collection for this study.”

That may have tainted the results, he said.

During a telephone press conference, planned before the paper was released, Lazovich said, “I am not an advocate, I am a cancer researcher.”

She said the work Levy referred to was a study looking at business practices in the tanning industry that included “pilot training materials” to encourage operators to adhere to regulations.

That research, she said, was supported by the National Cancer Institute and peer-reviewed by the NIH.

The current study represents “a very important addition to the body of data” on the risks of tanning devices, according to dermatologist Allan Halpern, MD of New York’s Memorial Sloan-Kettering Cancer Center.

In dermatology, he told reporters during the press conference, “we see the horrible price paid for using these devices.”

He noted that a recent FDA advisory panel recommended strongly that young people not use the machines, although the agency has not yet made such a change to regulations. (See Minors Shouldn’t Use Tanning Beds, Panel Says)

But getting people out of the tanning salons will take a change in “social norms,” said Electra Paskett, PhD, of the Ohio State University Comprehensive Cancer Center in Columbus.

For many adolescents, she said, tanning salons are now a routine part of life, which means their parents are going to have to step in.

On the positive side, there is no biological dependence to be overcome, as there is with such things as tobacco and alcohol, Paskett said.

Michael Smith is a MedPage Today North American Correspondent.

Originally published in MedPage Today. Visit MedPageToday.com for more skin cancer news.