Starting hormone replacement therapy within five years of menopause may cut the risk of developing Alzheimer's disease by 30 percent in women, a new study suggests.

The study followed 1,768 women ages 65 and older for 11 years. All the participants provided a history of their hormone therapy use and the date at which they started menopause. Researchers said that 1,105 women in the study had used hormone therapy, consisting of estrogen alone or in combination with a progestin, and 668 women had not.

Researchers said that during the study, 176 women developed Alzheimer's disease, including 87 women from hormone therapy group and 89 women in the control group.

Researchers compared the results of women who began hormone therapy within five years of menopause to the control group and found that those who had started hormone therapy had a 30 percent lower risk of Alzheimer's than those who had not used hormone therapy.

Results from the study, published in the journal Neurology, revealed that there was no difference in the risk of developing Alzheimer's disease in women who had begun hormone treatment more than five years after menopause.

However researchers noted that women who had started a combined therapy of estrogen and progestin when they were older than 65 years old had a higher risk of dementia.

"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," study author Peter P. Zandi of Johns Hopkins University in Baltimore said in a statement. "On the other hand, if started later in life, hormone therapy could be associated with an increased risk of developing Alzheimer's disease."

Experts said that the latest findings suggest that short-term hormone use may reduce the risk of Alzheimer's disease. However, more research is needed before new clinical recommendations can be established for women and their use of hormone therapy.

"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," Dr. Victor Henderson of Stanford University in Stanford, California wrote in an accompanying editorial.

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