Health risks related to hormone therapy with estrogen might go away after women stop the treatments, a new study suggests.

The results are good news for women in their 50s, said Graham Colditz, a professor at the Washington University School of Medicine, because that’s the age group most likely to take hormones to treat menopause symptoms.

“But that doesn’t mean continuing to take them for five to 10 years won’t have some risks emerge,” Colditz, who wrote an editorial that was published along with the study, told Reuters Health.

The new research focused on some of the same women who participated in a study that first raised concerns about the safety of hormone therapy. The women all had undergone hysterectomy before joining the study; after joining, they were assigned to a group that received estrogen pills.

Findings from the federally-funded study, called the Women’s Health Initiative, showed in 2004 that taking estrogen by itself increased women’s risk of stroke and did not reduce the risk of coronary heart disease.

But now, several years after the women stopped taking the estrogen, their risks for complications - including not just strokes and blood clots but breast cancer and heart problems - have returned to normal, according to a report in the Journal of the American Medical Association.

The results apply only to women in their 50s, and only to those taking estrogen after a hysterectomy; for older women taking a combination of hormones, the risks tied therapy persist.

Hysterectomy - removal of the uterus - is the second most common surgery among women, and one third of women have had a hysterectomy by age 60. Estrogen by itself can lead to cancer of the lining of the uterus; that’s why women who have a uterus and need hormone therapy must take a combination instead of estrogen alone.

The original findings from the Women’ Health Initiative contributed to ending the practice of prescribing hormone therapy to women for preventing heart disease, said Colditz.

But many women who have had a hysterectomy use estrogen to relieve the symptoms of menopause, “although questions remain regarding the safety of this treatment,” Colditz wrote.

The new study followed 7,645 women for 10 years - six years during hormone treatment and four years after ending the treatment.

Women randomly assigned to take hormone therapy used Premarin, a hormone therapy made by Wyeth, a pharmaceutical company now owned by Pfizer.

During the treatment, stroke was 36 percent more likely and blood clots were 47 percent more likely among women who took estrogen compared to those who didn’t.

That meant 45 out of every 10,000 women taking hormone therapy had a stroke compared to 34 out of every 10,000 women who didn’t take estrogen.

And 23 of every 10,000 women taking estrogen had a blood clot compared to 15 out of every 10,000 women who were not on the treatment.

However, after 10 years, there was no significant difference between the groups for these conditions.

For women in their 50s, estrogen treatment even appeared to have some benefits over time.

The hormones were linked to a 46 percent drop in the risk of a heart attack and a 27 percent drop in the risk of dying after 10 years.

That translated to 12 fewer heart attacks and 13 fewer deaths for every 10,000 women in this age group.

For women in their 70s, however, those benefits were missing, and for some conditions their risks were increased if they took estrogen.

The authors wrote that estrogen therapy was tied to 16 extra heart attacks and 19 additional deaths among women in this older age group at the end of the 10 years.

“If you’re a woman in your 70s, there’s very little reason to initiate estrogen,” Dr. Andrea LaCroix, of the Fred Hutchinson Cancer Research Center in Seattle and the lead author of the study, told Reuters Health.

Though the risk of breast cancer in this study appeared to be the same between women who took estrogen and those who didn’t, Colditz said other studies have found a link between the cancer and the hormone therapy.

A different arm of the Women’s Health Initiative - which ended in 2002 - found an increased risk of breast cancer and heart disease among women who took estrogen plus progesterone hormone therapy.

Colditz added that it’s not clear what the age limit or length of time on estrogen therapy should be to provide the most benefit and the least risk.

The women in this study adhered to the estrogen regimen for an average of three and a half years, and continued to take the hormone at some level for a total of six.

“Some women are long term hormone therapy users and they don’t want to stop,” LaCroix said. “Our data don’t speak clearly for them.”

SOURCE: Journal of the American Medical Association, April 5, 2011.