Women who use tanning beds during adolescence and early adulthood and who get multiple sunburns during their teen years may have an increased risk for endometriosis, a recent study suggests. Researchers examined data from a cohort of 116,429 female participants in the Nurses' Health Study II, who enrolled in 1989 when they were 25 to 42 years old and were followed through June 2015. By the end of the study period, a total of 4,791 women out of 95,080 included in the final analysis were diagnosed with laparoscopically-confirmed endometriosis. Compared to women who never used tanning beds, those who used tanning beds at least six times per year during high school and college (hazard ratio 1.19) or from age 25 to 35 (HR 1.24) were more likely to develop endometriosis, researchers report in Human Reproduction. Women with five or more sunburns during adolescence were also at increased risk for endometriosis (HR 1.12) compared to women without reported sunburns. "These results reinforce existing evidence that all women should avoid activities that involve high-intensity sun exposure and increase the possibility of sunburns, like using tanning beds," said lead study author Leslie Farland, an assistant professor in the department of epidemiology and biostatistics at the University of Arizona in Tucson. "We know that these types of high-intensity sun exposures increase risk of skin cancer and our research suggests that these types of exposures may also be associated with an increased risk of endometriosis," Farland said by email. Past research into long-term consequences of endometriosis have found an increased risk of melanoma, the researchers note in their report. While the exact mechanisms underlying the association between endometriosis and melanoma are not known, several previous studies have also found a greater risk of endometriosis in women who are sensitive to sunlight, don't tan easily and have red hair, light eyes, freckling or a high number of moles, the study team points out. It's possible that melanoma and endometriosis share risk factors, such as high exposure to UV-A radiation from recreational tanning, they add. However, the current study also found that women living in parts of the country with high levels of ultraviolet light throughout the year, such as southern parts of the U.S., had a lower risk of endometriosis (HR 0.81) than those living in regions with low residential UV. This might suggest that residential exposure favors UV-B light and formation of protective vitamin D levels, the authors speculate. When participants joined the study, they completed questionnaires about their tendency to sunburn, the number of moles on their legs, and the number of severe sunburns they experienced between the ages of 15 and 20 years. Participants completed questionnaires every two years, providing periodic updates on their usage of sunscreen, tanning beds, any endometriosis diagnosis, and a home address that could be used to determine their exposure to ambient ultraviolet A and ultraviolet B light. Women were excluded from the analysis if they reported a history of endometriosis, melanoma, or other forms of skin cancer at enrollment. Researchers also limited the analysis to white women due to known racial disparities in endometriosis risk and the impact of UVA and UVB exposure. One limitation of the study is that participants may not have accurately recalled or reported on past exposure to the sun or prior usage of tanning beds, the study team notes. Another limitation is that results from this analysis of data from white women working as nurses may not be generalizable to women in other professions or from other racial or ethnic groups. "My interpretation of the results of this study is that when it comes to UV exposure it is a good thing in moderation and a bad thing in excess, as is already well documented from cancer research," said Peter Rogers, a professor of women's health research in the department of obstetrics and gynecology at the University of Melbourne in Australia who wasn't involved in the study. "The potential biological mechanisms leading from UV to endometriosis are a little harder to understand at the present time and will require a lot more work," Rogers said by email. —Lisa Rapaport Source
