Postmenopausal estrogen therapy may increase kidney stone risk

The use of estrogen therapy by postmenopausal women might increase the risk of developing kidney stones, according to findings by researchers from the University of Texas Southwestern Medical Center, Dallas.

Estrogen therapy after menopause increased a woman’s chances of developing kidney stones by approximately 20%, the investigators found. They say this discovery calls into question the long-held belief that estrogen might actually protect women from the disease, said first author Naim Maalouf, MD.

"This research suggests that the opposite might be true, and it offers new information that might be considered when prescribing estrogen-replacement therapies to postmenopausal women," Dr. Maalouf said. "Because the process of kidney stone formation is influenced by a variety of lifestyle and other health-related factors, the true impact of estrogen therapy on the risk of nephrolithiasis is difficult to infer from observational studies."

A total of 10,739 postmenopausal women who had undergone hysterectomies were randomized to receive an estrogen supplement or a placebo, and 16,608 postmenopausal women who hadn’t undergone hysterectomies were randomized to receive estrogen plus progesterone or placebo. The rate of nephrolithiasis was determined for an average follow-up of 7.1 years for the estrogen-only group and 5.6 years for the second group.

In women receiving hormones, 335 cases of kidney stones were reported, while 284 cases occurred in the placebo groups. Development of kidney stones during the study was five times more common in women who had a history of kidney stones prior to the trial. Additionally, estrogen therapy increased the risk of kidney stone formation irrespective of age, ethnicity, body mass index, prior hormone therapy use, or use of coffee or thiazide diuretics.

Study results were published in the Archives of Internal Medicine (2010; 170:1678-85).