A new study suggests that women who begin taking hormone therapy within five years of menopause may reduce their risk of developing Alzheimer's disease. The research is published in the October 24, 2012, online issue of Neurology®, the medical journal of the American Academy of Neurology.

"This has been an area of debate because observational studies have shown a reduced risk of Alzheimer's disease with hormone therapy use, while a randomized controlled trial showed an increased risk. Our results suggest that there may be a critical window near menopause where hormone therapy may possibly be beneficial," said study author Peter P. Zandi, PhD, with Johns Hopkins University in Baltimore. "On the other hand, if started later in life, hormone therapy could be associated with an increased risk of developing Alzheimer's disease."

For the study, researchers followed 1,768 women ages 65 and older for 11 years. The women provided a history of their hormone therapy use and the date at which menopause began. A total of 1,105 women had used hormone therapy, consisting of estrogen alone or in combination with a progestin. During the study, 176 women developed Alzheimer's disease dementia, including 87 of the 1,105 women who had taken hormone therapy compared to 89 of the 663 others.

The study found that women who began hormone therapy within five years of menopause had a 30-percent lower risk of Alzheimer's dementia than those who had not used hormone therapy. The risk was unchanged among other hormone users who had begun treatment more than five years after menopause, but a higher risk of dementia was observed among women who had started a combined therapy of estrogen and progestin when they were at least 65 years old.

"While this well-designed study supports the possibility that short-term hormone use may reduce the risk of Alzheimer's disease, more research is needed before we can make new clinical recommendations for women and their use of hormone therapy," said Victor Henderson, MD, MS, with Stanford University in Stanford, Calif., and a Fellow of the American Academy of Neurology, who wrote an accompanying editorial.

The study was supported by the National Institute on Aging.