Endometriosis more common in lean women: study

Heavy women are less likely to be diagnosed with endometriosis than their slimmer peers, according to a new study.

Researchers following more than 116,000 women found that morbidly obese study participants were 39 percent less likely than normal-weight women to develop the chronic condition - in which uterine tissue grows outside the uterus and causes painful periods and bleeding.

That link was especially strong among women with infertility, according to Dr. Divya Shah from the University of Iowa Hospitals and Clinics in Iowa City and her colleagues.

Still, Shah told Reuters Health the findings don't prove that carrying around extra pounds protects against endometriosis, which affects more than 5 million women and teen girls in the U.S.

"By no means would I suggest ever that someone gain weight to try to reduce the risk of endometriosis," she said.

Shah and her colleagues used data from a long-term study of female nurses who were tracked beginning in 1989, when they were 25 to 42 years old. Women reported their height and weight as 18-year-olds and updated researchers on their weight and any new medical diagnoses every two years.

Between 1989 and 2011, about 5,500 of them were diagnosed with endometriosis.

Endometriosis is a female health disorder that occurs when cells from the lining of the womb (uterus) grow in other areas of the body. This can lead to pain, irregular bleeding, and problems getting pregnant (infertility). Causes

Every month, a woman's ovaries produce hormones that tell the cells lining the uterus (womb) to swell and get thicker. The body removes these extra cells from the womb lining (endometrium) when you get your period.

If these cells (called endometrial cells) implant and grow outside the uterus, endometriosis results. The growths are called endometrial tissue implants. Women with endometriosis typically have tissue implants on the ovaries, bowel, rectum, bladder, and on the lining of the pelvic area. They can occur in other areas of the body, too.

Unlike the endometrial cells found in the uterus, the tissue implants outside the uterus stay in place when you get your period. They sometimes bleed a little bit. They grow again when you get your next period. This ongoing process leads to pain and other symptoms of endometriosis.

The cause of endometriosis is unknown. One theory is that the endometrial cells shed when you get your period travel backwards through the fallopian tubes into the pelvis, where they implant and grow. This is called retrograde menstruation. This backward menstrual flow occurs in many women, but researchers think the immune system may be different in women with endometriosis.

Endometriosis is common. Sometimes, it may run in the family. Although endometriosis is typically diagnosed between ages 25 - 35, the condition probably begins about the time that regular menstruation begins.