Slim women have a higher risk of developing endometriosis than women who are morbidly obese, according to a new major study.
The research was published in the journal Human Reproduction and showed that morbidly obese females (BMI greater than 40 kg/m2) have a 39% lower risk of endometriosis than females with a current BMI in the low normal range (8.5 to 22.4 kg/m2).
When the investigators looked back at the subjects’ BMIs when they were 18 years old, they found that those who were morbidly obese at that age had a 41% reduced risk of endometriosis than those with low normal BMI.
The link was strongest in the group of females who were barren – i.e. those who had been trying to conceive for over a year.
In that group, the rate of endometriosis was notably lower among the currently morbidly obese (62%) than women with a low normal BMI, and the rate was 77% lower among those who were morbidly obese when they were 18 than those with a low normal BMI at that age.
The results of the research demonstrate a strong association between endometriosis and BMI, however, does not indicate that low BMI causes the condition, the authors explained.
The investigators said:
“It is important to note that despite the strength of the evidence underlying the association between body weight and endometriosis, inferences regarding causation or the pathophysiologic process underlying these relations cannot be made.”
Although the mechanisms behind the association between BMI and endometriosis risk are not known, BMI at a younger age might have an impact on a person’s well-being later in life, the researchers said, because it can have an influence on other illnesses.
Additionally, obese women are more frequently diagnosed with polycystic ovarian syndrome (PCOS), the effect it has on menstruation and hormones may be responsible for decreasing or slowing the growth of endometrial lesions.
Divya Shah (MD), study author and Clinical Assistant Professor at the University of Iowa Hospitals and Clinics, said:
“Further research is needed to understand the biological mechanisms underlying the associations that we have seen in our study. Maintaining a healthy body weight (BMI 20-24.9 kg/m2) throughout childhood, adolescence, and adulthood is associated with a myriad of known health benefits.
The study does not suggest that the morbidly obese women are, in some way, healthier than the lean women and that is the reason for their lower risk of endometriosis. It is more likely that factors related to infertility, which is more common among the very obese, are linked to the reduced risk of endometriosis.”
The experts gathered and analyzed data from the Nurses’ Health Study II (NHS II) which has been observing female nurses in the U.S. since September 1989. They looked at over 20 years’ worth of data – from 1989 until June 2011.
A diagnosis of endometriosis was given to 5504 women during that period. All participants were between 25 and 42 years old when they signed up for the study in 1989.
The subjects were asked to fill out a questionnaire about their medical history at the start of the study, including measurements of their weight and height at the age of 18, and then every two years.
The team also looked at current weight, height, and from 1993, waist and hip circumference, and any diagnosis of laparoscopically-confirmed endometriosis.
Senior author, Associate Professor, Stacey Missmer (ScD), of Harvard Medical School in Boston, USA, said:
“This study confirms that women with a low BMI, both currently and at age 18, have a greater risk of developing endometriosis. The association remains stronger in infertile women, but is present in all women regardless of fertility status.
Insomuch as any data can ever claim to be definitive, we do believe that this large prospective study provides conclusive evidence of the inverse association between endometriosis and BMI.”
Approximately one in 10 women of reproductive age is affected by endometriosis. Since a laparoscopy is the only way to diagnosis the condition, it is virtually impossible to know exactly when endometriosis started.
However, the scientists pointed out that a previous report on females in 16 centers in 10 countries revealed that the mean age at which symptoms begin is 26, and most patients do not receive a conclusive diagnosis until six or seven years after the onset of symptoms.
A previous study in Gut showed that women with endometriosis are nearly twice as likely to develop inflammatory bowel disease than other females.
Written by Sarah Glynn