Women who begin hormone replacement therapy at a certain age may have a lower risk of dementia, according to a new study. The findings point to a potentially important association while stopping short of showing that the treatment prevents the condition.

The study was published in Alzheimer’s & Dementia and examined UK Biobank data from 183,450 postmenopausal women. Participants were an average of 60 years old.

Over a follow up period of 13 years, the U.K. researchers found that HRT use was associated with about a 10% lower risk of all cause dementia. It was also associated with a 16% lower risk of Alzheimer’s disease.

The association was strongest among women who began hormone therapy between the ages of 46 and 56. Researchers also observed a strong association among women who had experienced surgical menopause.

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However, beginning HRT after age 56 was not associated with a reduction in dementia risk. The findings therefore suggest that the age at which women start treatment could be an important factor in the observed association.

Dr. Alexa Fiffick, a board certified family medicine physician and founder of Concierge Medicine of Westlake in Cleveland, Ohio, emphasized that the research was observational. That type of study cannot establish cause and effect.

The researchers offered the same caution, noting that their findings showed an association rather than proof that HRT prevents dementia. The study also did not evaluate safety outcomes or adverse events connected to hormone therapy.

Women who use HRT could differ from women who do not use it in ways that influence dementia risk. Those differences could include overall health, lifestyle and access to healthcare.

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Although the researchers adjusted for many relevant factors, they acknowledged that unmeasured differences could still contribute to the lower risk recorded among HRT users. Most participants were also of European ancestry and tended to be better off financially.

As a result, the findings may not apply equally to people from other populations. The study also lacked detailed information about the types of hormone therapy used, how the treatments were administered and the specific dosages taken.

Fiffick said the study by itself likely does not justify pursuing HRT solely to prevent dementia. However, she encouraged women experiencing symptoms or feeling unlike themselves to discuss the issue with a physician.

"However, if you're having symptoms, if you feel not yourself, come in, talk to your doctor, have that conversation," she advised. Fiffick said the discussion can help address a patient’s individual circumstances.

Some data have linked menopausal symptoms, including hot flashes and night sweats, to vascular changes in the brain, according to Fiffick. However, evidence showing that treating those symptoms prevents vascular changes that lead to vascular dementia is not currently available.

"So, we are very hopeful to see that treating those symptoms may prevent the vascular changes that lead to vascular dementia, but we just don't have that data right now," she said. "So, it's worth the conversation, it's worth bringing up, but I wouldn't go out of your way for just this purpose."

HRT also carries known risks and side effects, Fiffick noted. Oral forms of estrogen may raise the risk of blood clots, while that risk does not appear to exist with transdermal options such as patches, gels and creams.

Other forms of HRT may affect breast activity, overall inflammation, cardiovascular markers and cardiometabolic markers, according to Fiffick. Because treatments and individual circumstances differ, she stressed the need for a detailed medical discussion.

"So, it's not one size fits all, and it's really worth an extensive conversation." The researchers now plan to conduct randomized controlled trials to determine whether HRT reduces dementia risk.

Future research will examine estrogen only therapy compared with combined therapy, as well as dosage, administration route and treatment duration. Researchers also plan to consider age when therapy begins, menopause type and potentially APOE genotype.

"I think the more we have studies like this, the more we're going to propel forward the randomized controlled trials to really give women the data they deserve," Fiffick concluded. "Women deserve to have information to use to make decisions about their bodies. So I'm excited to see the trends heading in that direction."