By Steven Reinberg
Based on this finding, the researchers believe there's no reason to use hormone replacement therapy to boost mental well-being after periods stop.
"These study findings provide further evidence that a woman's decision about hormone therapy use during early postmenopause should be made independently of considerations about thinking abilities," said lead researcher Dr. Victor Henderson, a professor of neurology and neurological science at Stanford University in California.
However, while estrogen wasn't tied to any mental benefits, the study found that another hormone -- progesterone -- might affect thinking ability in younger women.
But this could be a chance finding and merits further investigation, according to the report, published online Nov. 25 in the Proceedings of the National Academy of Sciences.
The benefits and harms of hormone replacement therapy have been the subject of much debate. Previous studies have linked use of synthetic hormones after menopause with increased risk for heart disease, stroke, blood clots and breast cancer.
Dr. Jennifer Wu, an obstetrician/gynecologist at Lenox Hill Hospital in New York City, said that after menopause "a lot of women think that lack of estrogen will lead to mental decline, and that's just not the case."
Doctors don't usually start with hormone replacement therapy as the first line of treatment for postmenopausal symptoms because of the associated risks, she said.
"Trying to maintain mental abilities is not a reason to take on all the risks of hormone replacement therapy," she said. And other medications are available for treating hot flashes -- episodes of intense body heat related to menopause.
Some scientists theorized that estrogen's effect on thinking might depend on how soon after menopause hormone levels were boosted. This led the researchers of this study to divide the participants into two groups -- women within six years of menopause and those more than 10 years beyond menopause.
Henderson said length of time in estrogen decline appeared to make no difference. "We found that the relation between blood levels of estrogen and memory or planning skills is the same in younger postmenopausal women as in older postmenopausal women," he said. "Essentially, for estrogen there is no association at either age."
Although these findings don't absolutely rule out estrogen as relevant to thinking and memory, since there is no direct way of measuring estrogen in the brain, they suggest that boosting estrogen levels -- even in younger postmenopausal women -- may not affect mental skills one way or the other, he said.
Dr. Marc Gordon, chief of neurology at Zucker Hillside Hospital in Glen Oaks, N.Y., agreed that this finding doesn't "support the hypothesis that younger postmenopausal women would be more responsive to the beneficial effects of estrogen on their mental abilities."
He also said the correlation between higher progesterone levels and better memory and thinking skills in younger women needs to be replicated. "It is not yet clear what the effect of this sex hormone on the brain may be," he added.
The study relied on data on more than 600 postmenopausal women, aged 41 to 84. None of them was using hormone replacement therapy.
Researchers administered a series of tests to gauge the women's memory and overall thinking skills. They also assessed them for depression, and measured levels of the hormones estradiol, estrone, progesterone and testosterone.