Does working the night shift cause endometriosis?

If you know what it’s like to clock in at 6:30 p.m. and clock out just as the sun is rising, you’re probably what most of us 9-to-5ers would call a hero. Whether you hear it often or nor, you are a hero because your job is so important that it can’t stop existing long enough for you to get a full night’s sleep. Working the night shift can cause a host of health problems, and only the strongest of the bunch can handle working night shifts for large chunks of time.

The Night Shift and Endometriosis

There are 5.3 million women in the United States who work hours that aren’t the usual 9-to-5. Of these women, 1.1 million work the night shift. In 2008, researchers at the University of Washington wanted to find out if working the night shift was related to endometriosis symptoms and surprisingly to some of us, they found a strong correlation between the two.

Working at all during night shift hours was found to increase the risk for endometriosis by 50%. Women who who worked more than half of their weekly shifts on the night shift doubled the risk for endometriosis. Women who worked more than half of their job hours during the night shift for longer than five years had the highest risk of endometriosis of anyone studied. So what’s the connection?

One theory regarding the connection between shift work and increased risk for endometriosis is that melatonin plays a role. Melatonin is the hormone produced by our bodies when it’s time to go to bed – it’s the sleep hormone. It is believed that melatonin may inhibit cancer growth. If this is true, melatonin may also inhibit the growth of endometrial cells. Women who work the night shift most likely have abnormal melatonin levels because their sleep-wake cycle does not sync up with the sun.

Another theory is that the high levels of stress faced by night shift workers could lead to a lack of gonadotropin release. Gonadotropins are the hormones that maintain fertility. It is believed that this type of sustained stress could exacerbate your body’s inflammatory response. This could lead to inflammation (and pain) of the endometrium.

Symptoms of Endometriosis

When endometrial tissue migrates outside of the endometrium, it can cause heavy bleeding, scarring and irritation throughout the organs of the pelvis. Most women with endometriosis begin to have symptoms as teens that last throughout adulthood until they are resolved with menopause.

Major symptoms of endometriosis include painful periods, painful urination and pelvic pain that occurs outside of the menstrual cycle. Some women with endometriosis also have pain with bowel movements and irritable bowel syndrome. Heavy periods, back pain, constant fatigue and painful bladder symptoms (including interstitial cystitis or IC) are also signs of endometriosis.


Marino, J. L., Holt, V. L., Chen, C., & Davis, S. (2008). Shift work, hCLOCKT3111C polymorphism, and endometriosis risk. Epidemiology (Cambridge, Mass.), 19(3), 477–484.

Content Sponsored by: MIRI Women – The Minimally Invasive Reproductive Surgery Institute (MIRI) brings together highly skilled, board-certified specialists who are focused on women’s health. Our team of professionals is trained in advanced gynecology, specifically hysterectomy surgery. Philosophically, our partner physicians take a “less is more” approach to health care, by first treating patients with the most conservative therapies. MIRI focuses on physical healing, while emphasizing that a patient’s emotional well-being is just as important.

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