Does sun exposure cause endometriosis?

Recent research has found that women, who had a history of intense exposure to the sun (usually associated with intention to tan and tanning bed use), were at greater risk of being diagnosed with endometriosis over time.

Conversely, women who lived in the sunniest locations with lower latitude (and thus higher ultraviolet (UV) radiation levels) as teenagers and young adults, were less likely to be diagnosed with endometriosis [1].

Studying sun exposure and endometriosis

We currently do not know whether sun exposure causes endometriosis or influences endometriosis symptoms.

Using data from more than 116,000 US nurses, who were enrolled in the Nurses’ Health Study II, women were asked detailed questions about their sun exposure in adolescence and early adulthood. The research team also calculated sun exposure based on the participant’s residential (home) addresses at different ages (birth, aged 15, and aged 30).

These women were then followed over time to see who were surgically confirmed to have endometriosis in the years after this sun exposure.

The research team found that (after accounting for other factors that may be associated with both sun exposure and endometriosis) women who used tanning beds six or more times a year when they were teenagers and young adults had nearly a 20% greater risk of endometriosis compared to women who never used tanning beds.

Women who used tanning beds six or more times a year between the ages of 25-35, had a 24% greater risk, and those who used tanning beds three or more times a year throughout both periods of their lives, had a 30% greater risk of endometriosis.

Conversely, women who lived in the sunniest parts of the United States at birth, age 15, and age 30, had a 19%, 21%, and 10% reduced risk of endometriosis respectively compared to women living in parts of the US with the least annual sunshine.

How could sun exposure influence endometriosis?

The exact mechanisms explaining how sun exposure may influence risk of endometriosis  are not yet clear. However, further research on this topic could help scientists and healthcare providers better understand new pathways of how endometriosis develops and how it can be treated related to sun exposure.

Said lead author, Leslie Farland:

Assistant Professor, Leslie Farland
University of Arizona

For example, we do know that tanning beds and high intensity exposure to sunlight lead to DNA damage, cell damage, immunosuppression, and inflammation, which increase the risk of skin cancer.

It is plausible that these same mechanisms are at play to increase endometriosis risk also, given the known aberrant immune and inflammatory response in endometriosis.

Conversely, residential sun exposure reflects chronic exposure to UV radiation. Our measurement more heavily weights the shorter, UVB wavelengths that catalyse vitamin D production within the body.

Thus, the decreased risk of endometriosis associated with residential sun exposure may suggest a beneficial vitamin D pathway – but further research is needed to better understand these potential associations.

The role of vitamin D

Vitamin D influences immune function and earlier research has suggested that vitamin D acquired from diet may reduce risk of endometriosis [2].

Women can acquire vitamin D from their diet and from the sun, but the majority of circulating vitamin D is derived from the sun.

What do these findings mean for women with and without endometriosis?

This research adds to the existing evidence that all women should avoid activities that involve high-intensity sun exposure, like tanning bed use—as we know these exposures increase the  risk of skin cancer and this recent research suggests they may also increase the risk of endometriosis.

  1. Farland LV, et al. Recreational and residential sun exposure and risk of endometriosis: a prospective cohort study. Hum Reprod 2020
  2. Harris HR, et al. Dairy-food, calcium, magnesium, and vitamin D intake and endometriosis: a prospective cohort study. Am J Epidemiol 2013;177(5):420-30.
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