Kidney stones should be added to the list of health problems linked with hormone pill use after menopause, according to an analysis of landmark government research that first raised alarms about the products.
Among more than 24,000 postmenopausal women taking either hormones or dummy pills, those using hormones were 21 percent more likely to develop kidney stones over about five years.
Those results suggest that over a year's time, among 10,000 postmenopausal women taking hormones, five would develop kidney stones who wouldn't have if they hadn't used the pills.
The risks were similar for women taking Prempro, pills containing estrogen plus progestin _ or Premarin, estrogen-only pills.
Recent data suggest that overall, about 6 percent of postmenopausal women develop kidney stones.
Dr. Naim Maalouf, the study's lead author, said women considering using hormones to ease hot flashes and other menopause symptoms should "look at the bigger picture," weighing those benefits against the risks for kidney stones but also for more serious problems the pills have been linked with, breast cancers, heart attacks and strokes.
The government now recommends that hormone replacement pills only be used to relieve menopause symptoms, in low doses for the shortest possible time. The new results on kidney stones are unlikely to change that advice.
The study appears in Monday's Archives of Internal Medicine.
Maalouf, an endocrinologist at the University of Texas Southwestern Medical Center in Dallas, joined colleagues in analyzing data on women who participated in the government's long-term Women's Health Initiative studies comparing older women taking Prempro or Premarin with those given dummy pills.
The studies were designed to examine hormones' effects on various ailments, but not specifically kidney stones. Still, women were asked periodically if they'd been diagnosed with kidney stones during the multiyear studies.
The Prempro study was halted early in 2002 and made international headlines when data showed more breast cancers, heart attacks and strokes in the hormone group. The other study was halted was in 2004 when Premarin was linked with strokes. Prempro later was linked with increased risks for dementia, and in women with lung cancer, more deaths.
Naturally occurring estrogen has been thought to protect against kidney stones, which are more common among men than in women younger than 50. Because of that, it was theorized that estrogen pills after menopause _ when women's hormone levels decline _ might also help, Maalouf said.
He said reasons why the opposite was found in the study are uncertain, although one possibility is that uric acid levels in the urine can increase when women are taking estrogen, and that may contribute to stone formation.
Kidney stones are hard crystals of calcium or other substances that separate from liquid in urine. Normally smaller than a pea, they can grow to be the size of pearls or even golf balls. They usually pass without treatment but even small ones can be excruciatingly painful until they break up or exit the body. Large stones sometimes are treated with noninvasive shock wave therapy or sometimes surgery.
Victoria Davis, a spokeswoman for Pfizer Inc. _ which took over Premarin and Prempro maker Wyeth Pharmaceuticals last year _ noted that the government research was not designed to examine kidney stone risk, and pointed to a less rigorous study that found no link between hormones and kidney stones.
Dr. Gary Curhan, an author of that study and a physician at Harvard's Brigham and Women's Hospital, noted that its participants were younger than those in the government research, which involved women aged 63 on average _ at least 10 years older than the typical age of those who start taking hormones. The age differences might explain the studies' different results, he said.
On the Net:
Women's Health Initiative: http://tinyurl.com/37q3xcm