Downside to Being Slim for Women

Endometriosis risk higher in women with a smaller body mass index

/ Author:  / Reviewed by: Robert Carlson, M.D

(RxWiki News) Though extra body weight comes with its own set of health concerns, having a few extra pounds might be helpful in protecting a woman's uterus. 

A new study found that slimmer women were more likely to develop endometriosis, a condition that can cause severe abdominal cramping and pain. 

This study's findings showed that body weight and fat distribution might be linked with the condition and women might have an opportunity to adjust their risk in early adulthood, according to the researchers.

"Severe cramps lasting too long? Talk to an OB/GYN."

In endometriosis, the lining of the uterus grows out into other areas of the body.

The study, led by Divya Shah, MD, clinical assistant professor in the Division of Reproductive Endocrinology and Infertility at the University of Iowa Hospitals and Clinics, aimed to find any links between endometriosis, a woman's body shape and her body mass index (BMI), a measure of height and weight.

The researchers looked at data from the Nurses' Health Study II involving more than 116,000 female nurses between September 1989 and June 2011. The researchers included data on 5,504 nurses with endometriosis who were diagnosed using laparoscopy.

The women reported their height and weight at age 18. They then reported their weight every two years. Measurements of their hip and waists were taken in 1993 and updated in 2005.

Women classified as obese had a BMI between 35 and 39.9 kilograms per square meter. A low to normal BMI was classified as 18.5 to 22.4 kilograms per square meter.

The researchers found that lower BMIs in women were linked with higher cases of endometriosis. The findings were similar for women's current BMIs and their BMI at 18 years of age.

Obese women had between 55 and 62 percent lower chance of developing endometriosis compared to women with a low to normal BMI.

Women who had a waist to hip ratio of less than 0.6 were almost three times more likely of having endometriosis than women with a ratio between 0.7 and 0.79, though the researchers noted that the number of women in this category was small. 

Women may have an "early window of exposure" in which to develop a larger body size that can ultimately affect their risk of developing endometriosis, the researchers said. 

"The magnitude of both relations was stronger in the subset of women with infertility," the researchers wrote in their report. "Waist circumference and weight change since age 18 were related to endometriosis risk only in the subset of infertile women."

The researchers noted that the number of women who have endometriosis but do not show symptoms is very low. Body weight was not necessarily the cause behind endometriosis risk. 

In addition, the study from which the researchers drew their data did not look at the specific stages of endometriosis. Further research is needed to understand why endometriosis occurs less often in women with a higher BMI, according to the researchers.

The study, supported by the Eunice Kennedy Shriver National Institute of Child Health and Human Development, was published online May 14 in the journal Human Reproduction. The authors did not declare any conflicts of interest.

Reviewed by: 
Review Date: 
May 13, 2013
Last Updated:
September 19, 2013