Researcher Victor Henderson, MD, says the findings suggest early use of estrogen may be protective for the brain. Henderson is a professor of health research and policy and of neurology and neurosciences at Stanford University.
The study showed that women who used any form of estrogen therapy before age 65 were about 50% less likely to develop any form of dementia, including Alzheimer's disease.
"We found that it didn't matter whether she took estrogen alone or in combination with progestin, whether she started at 50 or 60, or how long she took it for," Henderson tells WebMD.
The study was presented at the 59th annual meeting of the American Academy of Neurology.
Estrogen's Protective Effect
The new research involved about 2,500 participants in the Women's Health Initiative Memory Study who started taking hormone therapy before age 65.
The women were enrolled in the study from 1993 to 1998. Over the next five years, 106 of them developed any form of dementia, 53 of whom had Alzheimer's disease.
Results showed that women reporting previous hormone therapy were 46% less likely to develop any form of dementia and 64% less likely to develop Alzheimer's disease than women who did not take any hormone therapy before that age.
Henderson says that one drawback of the study is that participants were asked to recall if they had ever used hormone therapy as opposed to having researchers go through their medical records.
The Hormone Debate
The findings are sure to renew the debate about hormone replacement therapy (HRT). For decades, women were told that HRT -- usually a combination of estrogen and progestin, but sometimes estrogen alone -- would not just relieve hot flashes and other symptoms of menopause, but also could protect them against heart disease and other ailments.
Then the 2002 results of the Women's Health Initiative study seemed to show just the opposite: hormone replacement therapy actually raised the risk of heart attacks, strokes, and cancer. About two-thirds of women taking HRT quit.
Since then, the pendulum has begun to swing back a little.
"People may be softening their views," Ronald Petersen, MD, director of the Alzheimer's Disease Center at the Mayo Clinic in Rochester, Minn., tells WebMD.
"We may not have to be as frightened as we were," says Petersen, who did not participate in the study.
While Petersen says he would not prescribe HRT to younger women based on the new findings alone, he thinks studies like this will make doctors less reluctant to prescribe estrogen to women who really need it to relieve disabling hot flashes or other menopausal symptoms. He says he would try to limit treatment to a year or two until the symptoms passed.
Henderson stresses he doesn't think the findings should change clinical practice. He says previous research has shown that starting estrogen therapy after age 65 increases by 50% the risk of later developing dementia.
Petersen speculates that one possible reason for a harmful effect later on might be that after a certain point in a woman's life, HRT acts a catalyst for disease development.