Genetics may explain why certain women gain weight when using a popular birth control method, researchers say.
“For years, women have said that birth control causes them to gain weight but many doctors failed to take them seriously,” said lead author of the study, Dr. Aaron Lazorwitz, assistant professor of obstetrics/gynecology and family planning, School of Medicine at the University of Colorado, Aurora.
“Now we have looked at the genetics and found that the way genes interact with some hormones in birth control could help explain why some women gain more weight than others,” Lazorwitz mentioned in a press release at the university.
Beneath the skin is implanted the etonogestrel contraceptive implant. It contains etonogestrel, a form of progest that prevents ovulation, and is considered one of the most successful birth control types.
The researchers also checked the medical histories of 276 women who obtained the implant for the study. They found that these women had a median weight gain of about 7 pounds over a 27-month average use. Nearly three-quarters of women were getting weight.
Further work led the researchers to conclude that a substantial weight gain was associated with genetic variants in estrogen receptor 1 (ESR1) among some of the participants.
On average, while using the contraceptive implant, women with two copies of the ESR1 rs9340799 variant gained more than 30 pounds more than other women in the study.
Previous research found linkages between genetic variants of ESR1 and the functioning of other types of medication, the authors of the study noted.
While this study focused on the etonogestrel contraceptive implant, the researchers said other birth control medicines could have similar interactions with genes that cause weight gain.
“It’s important to better understand how individual genetic variation can impact the risk of adverse weight gain from a woman,” Lazorwitz said when using these medicines.
There is currently no way of identifying who will gain weight when using such medicinal products. Health care providers can provide advice on potential weight gain, or suggest non-hormonal forms of birth control such as copper intrauterine devices (IUDs), suggested by the study authors.
“As our knowledge of pharmacogenomics in women’s health grows, we will develop individualized therapy that can minimize the occurrence of adverse effects related to hormones, increase patient satisfaction and help avoid potential health risks associated with weight gain,” Lazorwitz said.
The research was recently published in the newspaper Contraception.