Women using depot medroxyprogesterone acetate (DMPA), commonly known as the birth control shot, gained an average of 11 pounds and increased their body fat by 3.4 percent over three years, according to a study conducted by researchers at the University of Texas Medical Branch (UTMB) and published in the American Journal of Obstetrics and Gynecology.
"Women and their doctors should factor in this new data when choosing the most appropriate birth control method," said lead author Abbey Berenson, from UTMB. "One concern is DMPA's link to increased abdominal fat, a known component of metabolic syndrome, which increases the risk of cardiovascular disease, stroke and diabetes."
The study followed three groups of women: those using DMPA, those using oral contraceptives, and those employing non-hormonal contraception (tubal ligation, condoms or abstinence). The DMPA users who discontinued this method and selected another form of birth control were followed for up to two additional years. Throughout the course of the study, the researchers compared changes in body weight and composition and took into account the influence of age, race, caloric intake and exercise, among other factors.
When the researchers compared all three groups, the DMPA users were more than twice as likely as women using non-hormonal or oral birth control to become obese over the next three years. "The findings are worrisome; however, more research is needed to determine if DMPA use directly contributes to obesity-related conditions and puts patients' overall health at risk," said Berenson.
Women using oral contraception did not gain more weight than those using a non-hormonal form of birth control. However, the study found that their body fat increased slightly while their lean body mass (muscle) decreased. Researchers said this was less likely among those women who exercised regularly and consumed a healthy diet that included increased protein intake.
According to Berenson, the mechanism by which DMPA causes an increase in weight gain and fat mass is not known, and no connection was found between DMPA use and caloric intake, fat consumption or amount of exercise on body mass changes. The findings seem to argue against the theory that weight gain could be due to the drug's perceived effects on increased caloric intake and decreased energy expenditure, but ongoing research is needed to confirm or discount varying possible explanations, she said.
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Source: University of Texas Medical Branch at Galveston