Tanning beds and sunbathing can be associated with an increased risk of endometriosis

Tanning beds and sunbathing not only increase a woman’s chances of developing malignant melanoma, the most dangerous form of skin cancer, but they may also be linked to an increased risk of developing endometriosis, according to new research.

A study of over 116,000 women in the United States, published today in Human reproduction, one of the world’s leading reproductive medicine journals, found that the risk of endometriosis increases the more young women used tanning beds, sunburns or sunscreen during adolescence and young adulthood.

However, the study also found that women living in parts of the country with high levels of ultraviolet light throughout the year, such as the southern parts of the United States, were less likely to be diagnosed with the painful condition, in which tissue similar to the lining of the uterus it begins to grow in other places such as the ovaries and fallopian tubes.

Professor Leslie Farland, assistant professor at the University of Arizona College of Public Health (USA), who led the research, said: “Previous research on the long-term health consequences of endometriosis has suggested that women with endometriosis are at increased risk of melanoma. Although the exact mechanisms underlying the association between endometriosis and melanoma are not known, several studies have found an increased risk of endometriosis in women who are sensitive to sunlight, do not tan easily and have red hair, light eyes, freckles or a high number of moles. These associations may reflect a common genetic background between endometriosis and melanoma, or an underlying association between sun exposure and the risk of endometriosis. “

Prof. Farland and her colleagues from the Harvard TH Chan School of Public Health, Michigan State University College of Human Medicine (USA) and the French National Institute for Health and Medical Research (INSERM), Université Paris-Saclay, Villejuif (France) studied 116,429 women who joined the US Nurses’ Health Study II in 1989 when they were between the ages of 25 and 42. Every two years, until June 2015, participants filled out questionnaires asking about their medical history and their exposure to risk factors for various chronic diseases. When they joined the study in 1989, participants were asked about their tendency to sunburn, the number of moles on their legs, and the number of severe sunburn between the ages of 15 and 20. In 1993 they provided information on their use of sunscreen and in 2005 they reported on their use of tanning beds during adolescence and early adulthood and between the ages of 25 and 35.

From 1993 onwards, participants were also asked if they had endometriosis, diagnosed laparoscopically, which is the gold standard for correctly diagnosing the condition. Their home addresses were updated every two years and linked to annual ultraviolet A and ultraviolet B ambient light data for the area.

The researchers excluded from their analysis women who reported having endometriosis or who had been diagnosed with cancer (including non-melanoma skin cancer) at the time of joining the study. They also limited the analyzes to white women, given the known racial and ethnic disparities in diagnosing endometriosis and the differences in the influence of UVA and UVB light for different races.

Among the 95,080 women included in the analyzes, there were 4,791 cases of endometriosis diagnosed with laparoscopy in the follow-up period.

After adjusting their analyzes to account for factors that could influence the results, the researchers found that compared to women who never used tanning beds, those who used them six or more times a year when they were teenagers and young adults had a 19% increased risk of endometriosis. If they used them six or more times a year between the ages of 25 and 35, they had a 24% higher risk and if they used tanning beds three or more times a year in both periods of their lives, they had a 30% increase in risk of endometriosis.

This means that about five in 100 women could develop endometriosis in an average follow-up period of nearly 14 years per person if they had never used tanning beds as teenagers, young adults, or between the ages of 25 and 35, but nearly seven 100 women would develop it if they used tanning beds more than three times a year.

A history of five or more sunburns between the ages of 15 and 20 has been associated with a 12% increased risk of endometriosis compared to women who have never been sunburned. Compared to those who never used sunscreen, which the researchers used as an indicator of time spent sunbathing or participating in other outdoor recreational activities, those who used it all the time had a 10 higher risk of endometriosis. %. The absolute risk of developing endometriosis among women who were sunburned five or more times a year between the ages of 15 and 20 was too small to show a difference between the two groups.

Women who lived in the sunniest parts of the country at birth, at the age of 15 and 30, had a reduced risk of endometriosis of 19%, 21% and 10%, respectively, compared to women living in parts of the United States with the fewer sunshine per year. This means that four in 100 women could develop endometriosis if they lived in parts of the country with the highest UV levels at age 15 compared to nearly six in 100 if they lived in parts of the country with the lowest UV levels.

Professor Stacey Missmer, professor at Michigan State University College of Human Medicine and Harvard TH Chan School of Public Health and co-lead author of the study, said, “We know very little about ways to modify behavior in order to reduce the risk of developing endometriosis. There is still much we do not understand about the relationship between recreational and residential sun exposure and the risk of endometriosis. However, our results suggest that avoiding excessive recreational sun exposure and tanning beds can reduce the risk of endometriosis “.

Endometriosis is estimated to affect about 10% of women. This is the first prospective study of the association between sun exposure and endometriosis, and the researchers say their findings need to be further studied in other settings and with other groups of women.

“In the past 30 years, more people have been diagnosed with skin cancer than all other cancers combined,” said Prof. Farland. “From a public health perspective, we already know that women should avoid tanning beds to reduce their risk of melanoma. This study reinforces the advice to avoid the use of tanning beds and suggests that there may be an added benefit in reducing the Risk of Endometriosis Women should follow health advice to never use tanning beds, to avoid sunburn and to protect skin from sun exposure by covering up, seeking shade and using a broad spectrum UVA / UVB sunscreen. “

The mechanisms between exposure to the sun and tanning beds and the risk of endometriosis are unclear and, as the study is observational, it cannot demonstrate that these exposures cause an increased risk of endometriosis. The authors point out that high-intensity UV exposure is associated with DNA damage, cell damage, inflammation and melanoma risk and that tanning beds, in particular, emit predominantly UVA light, which has been associated with an increased risk. of cell damage and weakened immune responses. All of these have been linked to the risk of endometriosis. Conversely, if women live in sunnier parts of the world, they are exposed to more UVB light, which stimulates the production of vitamin D in the skin; vitamin D has been shown to suppress inflammation and boost immunity.

Other limitations of the study include that women may not have accurately remembered their sun exposure, particularly when they were younger; some may have been diagnosed with endometriosis before reporting on their recreational exposure in 2005; women in the Nurses’ Health Study II are not a random sample of US women; and the researchers’ analysis was limited to white women and therefore it may not be possible to extrapolate the results to women of other skin colors and ethnicities.

Editor in Chief of Human Reproduction, Dr. Nils Lambalk, from the Department of Reproductive Medicine, University of Amsterdam Medical Centers, Vrije Universiteit Amsterdam (Amsterdam, The Netherlands), commented: “This study sheds an intriguing light on the link between UV exposure and endometriosis. A psychological aspect that could be studied further if there could be a relationship between a woman’s self-image and endometriosis. For example, if you have endometriosis, this encourages you to look for ways to feel and look ‘better’ or ‘healthier’ through tanning? Or are women who are unhappy with their appearance also more prone to endometriosis? ”