Higher BMI connected to lower risk of endometriosis

Results of a study of more than 116,000 women, published online May 14 in Human Reproduction reveal a 39% lower risk of endometriosis in those who were morbidly obese than in women with normal body mass index (BMI).

Researchers at the University of Iowa studied the women, aged 25 to 42, between September 1989 and June 2011. The women reported their height and weight at 18 years old and informed the researchers every 2 years about any changes in weight and any new medical diagnoses. Over the course of the study, 5500 study participants had been diagnosed with endometriosis.

When comparing participants’ BMI at age 18 and at the current time, the researchers found that both served as indicators of the participants’ risk of endometriosis, with those with higher BMIs being less likely to develop the condition. The association between BMI and endometriosis was even stronger in women who suffered from infertility. Women with a BMI of 40 or more had a 62% (95% CI, 0.23-0.62) lower risk when compared to women with a low-to-normal BMI of 18 – 22.

The study’s lead author said that one reason for this outcome could be that women who are infertile because of polycystic ovary syndrome tend to be overweight and also frequently don’t develop endometriosis, which could skew the likelihood of endometriosis toward women at normal or low weights. Another possibility is that women develop symptoms of the condition many years before a diagnosis can be made. These symptoms may cause women to eat less, in turn leading to normal or low weight.