Estrogen Therapy Possibly Linked to Kidney Stones

Postmenopausal women using estrogen therapy could have an increased risk of developing kidney stones, according to a new study carried out by Naim M. Maalouf, MD, of the University of Texas Southwestern Medical Center, Dallas.

The researchers used data from two trials part of the national Women's Health Initiative study.

One trial included 10,739 postmenopausal women who had underwent a hysterectomy and received an estrogen-only treatment, or a placebo, and the second trial looked at 16,608 postmenopausal women without hysterectomy, who received a treatment including estrogen plus progestin, or a matching placebo.

For the first study, the authors gathered data for a 7.1 years period and for the estrogen plus progestin trial, for a 5.6 years period.

In the active treatment groups there were a total of 335 cases of kidney stones reported, while in the placebo groups, there were only 284.

After accounting for demographic characteristics and risk factors for kidney stones, the authors found that a significant increase in the risk of developing kidney stones was linked to estrogen therapy.

Every year, 39 out of 10,000 women in the treatment group developed kidney stones, unlike 34/10,000 of the placebo group.

The authors also observed that women with a history of kidney stones at the beginning of the study, had a five times higher risk, that was not remarkably altered by estrogen therapy.

Estrogen therapy proved to increase the risk of kidney stones development, regardless of age, BMI, ethnicity, prior hormone therapy use and coffee or thiazide diuretics use.

In the article, the authors say that “nephrolithiasis [kidney stones] is a common condition that affects 5 percent to 7 percent of postmenopausal women in the United States.

“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 kidney stone formation is difficult to infer from observational studies.”

As a conclusion, the results "indicate that estrogen therapy increases the risk of nephrolithiasis in healthy postmenopausal women.

“The mechanisms underlying this higher propensity remain to be determined.

“In view of the sizable prevalence of nephrolithiasis in this segment of the population, these findings need to be considered in the decision-making process regarding postmenopausal estrogen use."

The study was reported in the October 11 issue of Archives of Internal Medicine, one of the JAMA/Archives journals.