(HealthDay) -- Updated evidence on hormone replacement therapy for menopausal women presents good news for those at risk of osteoporosis, but a mixed bag of results regarding breast cancer and other chronic diseases.
While estrogen-only and estrogen-plus-progestin formulations reduce the risk of fractures, both increase the odds for stroke and other conditions including gallbladder disease, according to a new update of available evidence compiled for the U.S. Preventive Services Task Force, an independent expert panel that is revising its guidelines.
Estrogen-plus-progestin therapy raises the risk of breast cancer and probable dementia, while estrogen alone reduces the risk of breast cancer, the researchers found.
"We looked at all the published studies on hormone therapy for the prevention of chronic disease," said Dr. Heidi Nelson, who led the update. "What is new here is, we've taken all the results from the last 10 years and tried to distill them into the latest, most current results and how they might apply to individuals."
Some protective effects found in earlier research now appear weaker, added Nelson, a professor of medical informatics, clinical epidemiology and medicine at the Oregon Health & Science University, in Portland. Similarly, some risks look even stronger.
The findings are published online May 29 in the Annals of Internal Medicine.
Years ago, hormone therapy was often prescribed to prevent chronic conditions such as osteoporosis and cardiovascular disease. But initial results of the Women's Health Initiative study, published in 2002, found harmful effects for estrogen-plus-progestin regimens. Two years later, serious alarms were raised about estrogen-only therapy.
As a result, the task force recommended against both types of treatment for prevention of chronic disease.
Now, with about 11 years of follow-up to the Women's Health Initiative, researchers have a fuller picture, which the task force will use to update its existing guidelines.
The recommendations concern only chronic disease, not the use of hormone therapy for reducing symptoms of menopause, such as hot flashes.
For the update, Nelson and her team looked at 51 published articles, involving nine research trials, that met their criteria.
They confirmed that both estrogen alone and combination therapy reduce the risk of fractures, as found before. But they concluded that both types of treatment increase the risk of stroke, blood clots, gallbladder disease and urinary incontinence.
While estrogen alone seems to reduces the risk of breast cancer, they found stronger evidence than before that combination therapy increases the risk for breast cancer. For every 10,000 women, eight more cases of breast cancer per year are expected in those on combination therapy, Nelson said.
Women who smoke, used birth control pills or took combination therapy for symptoms of menopause have higher risks of breast cancer, they found.
Estrogen-only therapy appears to reduce invasive breast cancer by about the same amount, she said, but cautioned that it's not a reason for taking it. This effect is stronger than before, Nelson said.
Other changes: Initial results indicated that those on combination therapy had a significant increased risk for heart disease. Now, that association appears weaker, she said.
Previously, the estrogen-progestin combination was thought to protect against colon cancer. That link also looks weaker, she said.
Nelson said the differences in risks and benefits are probably explained more by the risk profiles of the women who take each therapy rather than the progestin or its lack in the therapy itself. The women have different risk factors to begin with, she said. For instance, many taking only estrogen have had a hysterectomy, with their uterus and ovaries removed, she said.
Bottom line? It does not appear wise to take hormone therapy long-term to prevent chronic conditions, she said. The best strategy remains to take the therapy, if needed for symptoms, at the lowest dose for the shortest time possible.
Given the different risks associated with estrogen-only and combination therapy, it's important to discuss your individual health history with your doctor, experts said.
Dr. Jill Rabin, chief of ambulatory care, obstetrics and gynecology at Long Island Jewish Medical Center, in New Hyde Park, N.Y., agreed that short-term, low-dose therapy for relief of symptoms is the best strategy.
Another option, she tells her patients, is to "think local." Some women are helped by estrogen cream or estrogen vaginal rings, she said.
Explore further: Combo hormone therapy has increased breast cancer risk over estrogen alone
More information: To learn more about hormone therapy, visit the U.S. National Institutes of Health.