A new study published this week in the journal Neurology showed that women who begin taking hormone therapy within five years of menopause may reduce their risk of developing Alzheimer’s disease. However, the study also found that women who start hormone therapy at a very late age could increase their risk of Alzheimer’s.

“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,” said Dr. Peter Zandi, lead author of the study and a professor at Johns Hopkins University. “Our results suggest that there may be a critical window near menopause where hormone therapy may possibly be beneficial. On the other hand, if started later in life, hormone therapy could be associated with an increased risk of developing Alzheimer’s disease.”

Zandi’s study looked at 1,768 women 65 years and older for 11 years. Using their history of hormone therapy use and the date at which they began menopause, the study found that those women who began hormone therapy within five years of starting menopause had a 30-percent lower risk of Alzheimer’s than those who did not use hormone therapy. The women who began hormone therapy more than five years after menopause did not have a significantly higher risk of dementia. However, women who started hormone therapy when they were at least 65 years old were found to have a higher risk for Alzheimer’s.