Use of tanning beds and sunbathing may increase women’s risk of developing endometriosis, researchers found in a first-of-its kind study uncovering a possible cause for the poorly understood and often painful gynecologic disease.
According to a paper published this month in Human Reproduction, women tracked over a quarter-century experienced significantly higher incidence of endometriosis if they engaged in heavy recreational sun exposure, through sunbathing or use of tanning beds. The study included 116,429 U.S. nurses of reproductive age, who were all white, in order to focus more specifically on association with sensitivity to UV radiation.
Although the study did not examine whether sunbathing and tanning beds specifically caused the illness, the data collected over a period of decades showed a compelling correlation, which may be useful for further study. Exact causes of the illness, which affects one in 10 women of reproductive age, or close to 190 million people worldwide, are unknown.
The work by lead author Leslie Farland, of the University of Arizona’s Department of Epidemiology and Biostatistics, and her team builds on previous research they did into a seemingly consistent relationship between endometriosis and melanoma, the deadliest form of skin cancer. The team has also looked into associations between the illness and sun-sensitive phenotypes such as light hair color and freckling.
“The conversation around sun exposure has kind of been in the background for a lot of prior research,” Farland told The Academic Times. “It made sense to then look at, directly, the relationship between sun exposures and risk of endometriosis.”
Endometriosis often flies under the radar for many women, in part because there are many barriers to receiving a diagnosis. It takes eight years on average to do so, according to a recent survey by Britain’s All-Party Parliamentary Group on Endometriosis.
The gynecologic disease occurs when tissue similar to the lining of the womb grows outside the uterus, in the ovaries or fallopian tubes, for example. Women can experience infertility, pelvic pain outside the menstrual cycle, pain during intercourse, urination, defecation and severe dysmenorrhea, in which uterine contractions cause painful menstrual periods.
“It’s a disease that often isn’t talked about,” Farland said. “We hope that these associations we’re seeing can be used in the future to help us better understand how endometriosis develops and potentially lead to new treatments or new ways to prevent endometriosis.”
The researchers examined the histories of the study participants and their self-reported use of tanning beds, instances and severity of sunburn and use of sunscreen as teenagers and young adults, which indicates recreational sun exposure. The study also accounted for sun exposure that occurred because of where the participant lived geographically.
Interestingly, while the research showed risk of endometriosis increased by as much as 30% for participants who engaged in heavy recreational sun exposure, residential exposure appeared to put women at a lower risk of developing the illness. Women who lived in the sunniest parts of the U.S. had a 10%-20% lower chance of developing endometriosis than women who lived in the parts of the country with the least annual sunshine.
The researchers hypothesized that residential exposure could be beneficial because natural sunlight contains shorter UVB wavelengths than tanning bed lights, and also because it can catalyze vitamin D production. Vitamin D plays an important role in regulating immune function, and previous research by the team has found that the nutrient may help protect women from the disorder.
“That’s the opposite of what we saw with these high-intensity intermittent exposures such as tanning, using tanning beds,” Farland said. “These really high-intensity but short-duration exposures may be leading to things like cell damage and inflammation.”
The research, published in a European journal, has so far has attracted more attention across the pond, where endometriosis has historically factored more in the public conversation. Women’s health advocacy groups have recently helped bring the issue to lawmakers in the U.K. as well as Australia through legislation and other means, Farland said.
The illness can be a challenging research topic, she said. Studies of the disease often only include women who have already been diagnosed, sometimes for years, making it difficult to identify causal factors.
“You could have a scenario where at the time of diagnosis, their behaviors have changed,” Farland said. “Maybe they’ve changed their diet or changed other things because they’re experiencing pain and they have been experiencing pain for decades, or for at least a few years before diagnosis."
The findings from this preliminary data now need to be replicated in other populations and cohorts of women, Farland said. This study was restricted to white women who were ages 25-42 when it began.
In the U.S., she hopes endometriosis becomes more widely discussed.
“Our research reinforces the public health message that we already know and we already tell women, which is to avoid those high-intensity sun exposures like using tanning beds because we know that those types of exposures increase risk of skin cancer,” Farland said. “The message from this research is they may also increase risk of endometriosis.”
The study “Recreational and residential sun exposure and risk of endometriosis: a prospective cohort study,” published Dec. 2 in Human Reproduction, was authored by Leslie V. Farland, University of Arizona; William J. Degnan, University of Arizona; Holly R. Harris, Fred Hutchinson Cancer Research Center and University of Washington; Jiali Han, Indiana University; Eunyoung Cho, Brown University and Harvard Medical School; Trang VoPham, Fred Hutchinson Cancer Research Center and Harvard T.H. Chan School of Public Health; Marina Kvaskoff, Université Paris Saclay; and Stacey A. Missmer, Harvard T.H. Chan School of Public Health, Boston Children's Hospital and Harvard Medical School, and Michigan State University.