Healthy postmenopausal women who receive estrogen therapy are at significantly increased risk of kidney stones, according to an analysis of data from 27,347 postmenopausal women in the national Women’s Health Initiative study.

Researchers examined data from two trials: 10,739 women who had a hysterectomy and received either an estrogen-only treatment or matching placebo and 16,608 who did not have a hysterectomy and received either an estrogen plus progestin treatment or matching placebo. Investigators collected data for an average of 7.1 years in the estrogen-only study and 5.6 years in the estrogen plus progestin study.

The annualized kidney stone incidence rate per 10,000 women per year was 39 among women using estrogen only or estrogen plus progestin, compared with 34 in women taking placebo, according to a report in Archives of Internal Medicine (2010;170:1678-1685).

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Although stone development was five times more common in women with a history of kidney stones at the beginning of the study compared to those without, it was not significantly altered by estrogen therapy. Estrogen treatment increased nephrolithiasis risk irrespective of age, BMI, progestin coadministration, prior hormone therapy use, use of thiazide diuretics, coffee intake, and ethnicity.