When compared to a placebo, estrogen plus progestin provided no protection against mild cognitive impairment and increased risk of dementia
But in the SWAN study, with much younger, peri-menopausal women, hormone therapy showed only positive cognitive benefits.
"At 50, many women are at the top of their careers and can't afford this," said Dr. Michelle P. Warren, director for the Center for Menopause, Hormonal Disorders at Columbia University Medical Center.
"For those two to five years when the symptoms are at their worst, we should treat these women," she told ABCNews.com.
But, she cautioned, women should weigh the risks versus benefits with the advice of their doctor.
"Women are scared to take hormones and doctors are scared to prescribe it," Warren said. "We have an issue that is very worrisome."
Menopause technically begins 12 months after a woman's final menstrual period when the ovaries no longer release eggs and there is decrease in the production of the sex hormones estrogen and progesterone.
But a whole array of bothersome symptoms can begin years earlier -- in peri-menopause -- as the woman's cycle transitions into menopause.
The process can begin in the 40s and accelerates until the early to mid 50s. Symptoms can include hot flashes, night sweats and fatigue, which, in combination with hormone fluctuations, can affect a woman's ability to concentrate and remember.
"My approach to this is if lose your job, your sanity or your husband, you do something about it," Warren said. "I see a lot of women about to lose their jobs because they cannot concentrate, they forget things or they are not sleeping. One of my patients had an auto accident. The consequences are very severe."
Another one of her patients was a lawyer in court presenting her arguments "when she drew a blank," Warren said. "Then she went to get her papers and couldn't find them. It was the most embarrassing thing in her life."
But the good news, according to the UCLA study, is that cognitive function rebounds once women reach menopause, though there is still a debate on what the longterm effects on brain function are.
"As long as there are hot sweats, the theory is that the neurons are sensitive to estrogen, but once you are more than five years out of menopause there is no benefit and, particularly as the brain ages, estrogen leads to deterioration," said JoAnn V. Pinkerton, president of the North American Menopause Society and director of the Mid-life Health Center at University of Virginia.
As far as the long-term effects of hormones on cognition, "there isn't a clear answer," according to Pinkerton.
"If you look at older women, you get mixed reports that estrogen prevents and increases Alzheimer's disease," she told ABCNews.com. "But it appears there is a critical window."
While the 2002 heart study showed "who shouldn't get estrogen" -- those over 60 -- newer research is pointing to a "critical window" in the stages of menopause when women can benefit from the hormone, according to Pinkerton.
A 2008 study on mice at Yale University suggested that estrogen has a beneficial effect on younger, healthy neurons, but a detrimental one on aging neurons, "perhaps even speeding up dementia," she said.