Hormone replacement therapy during menopause appears to be linked to a toxic brain protein that’s a hallmark of Alzheimer’s disease.

Women over 70 had a faster accumulation of tau in their brains if they’d taken hormone therapy for menopause symptoms more than a decade before, according to a new report in Science Advances.

Tau tangles are one of the hallmarks associated with Alzheimer’s, researchers noted.

Researchers did not find a significant difference in their accumulation of amyloid beta, another toxic protein linked to Alzheimer’s.

“Approximately a quarter of currently postmenopausal women who are 70 years and older have a history of HT use and have now entered a critical age of risk for Alzheimer’s disease,” senior researcher Rachel Buckley, a cognitive neuroscientist with Massachusetts General Hospital in Boston, said in a news release. 

But researchers found that hormone therapy among younger women did not appear to be linked with increased tau accumulations — supporting the notion that it should be safe early in menopause.

“Our findings add to the evidence that delaying initiation of hormone therapy, especially in older women, could lead to worse Alzheimer’s outcomes,” Buckley said.

For the study, researchers compared brain imaging from 73 women who’d used hormone therapy an average of 14 years earlier with 73 age-matched women who had not.

The participants underwent PET scans for amyloid beta over an average 4.5 years, and for tau an average 3.5 years.

Women 70 or older who used hormone therapy showed faster tau accumulation in specific regions of their brain, results show.

“Our data indicate that hormone therapy may influence tau accumulation as a function of age, with implications for cognitive decline,” lead researcher Gillian Coughlan with Massachusetts General Hospital said in a news release.

“We hope that our study will help to inform Alzheimer’s disease risk discussions relating to women’s reproductive health and treatment,” Coughlan added.