Hormone therapy was once linked to dementia. A huge study found it might lower risk

A growing body of evidence suggests hormone therapy can protect the aging brain, if it's timed right. Fiordaliso/Getty Images

Hormone therapy may protect a woman's aging brain, but timing is critical.

Experts agree the "window of opportunity" for HRT is typically in the late 40s or early 50s.

"Early intervention promotes and sustains brain health," neuroscientist Roberta Brinton said.

Get in there early. That seems to be the growing consensus around hormone replacement therapy (HRT) for women.

New study data suggests that middle-aged women could use these treatments to protect their brains, contradicting old concerns about a potential dementia risk.

There is a caveat to this good news: You probably have to adhere to what researchers are calling the golden "window of opportunity" before the brain hardens and ages too much. Start boosting estrogen levels too late, and you may be doing more harm than good for your brain health , a growing body of research suggests.

"Early intervention promotes and sustains brain health, and postmenopausal intervention does not," neuroscientist Roberta Brinton, the director of the Center for Innovation in Brain Science at the University of Arizona, told Business Insider.

Slowly, but surely, old stigma and fear about HRT are being replaced by data-driven optimism that these cheap, widely available hormone treatments may be longevity-boosting drugs — especially for the heart, for the brain, and for the bones — but only when used in the right way, at the right time.

"When you take all these data, they substantially point in one direction," Dr. Howard Hodis, a professor of medicine at the University of Southern California who's been studying the effects of hormone therapy on postmenopausal women for over three decades, said. "That is, early: good; late: maybe no effect, and maybe harmful."

Old fears about hormone therapy and dementia may not apply to women under 60

Hormone therapy can be administered through pills, patches, injections, or topical formulations like lotion or gel. Getty Images

For more than 20 years, there has been ongoing back and forth about how HRT for menopause may impact brain health and whether it's dangerous.

In the early 2000s, the Women's Health Initiative, a landmark, long-term study funded by the US National Institutes of Health, concluded that women taking HRT could have a slightly higher risk of many health issues, including heart disease, strokes , breast cancer, and dementia. The findings had a dramatic effect on how HRT was perceived and prescribed worldwide.

In the US, regulators put black box warnings on HRT starting in 2003 and rates of HRT use in postmenopausal women plummeted, from around 27% in 1999 to lower than 5% by 2020.

Even though other studies told a more complicated story about HRT use — and some suggested it could have a protective effect on the heart and the brain — the WHI was seen as a large, gold-standard study, and it spooked a lot of people.

After more than two decades of additional research, experts question some of the WHI's earlier methods. The study focused primarily on older women. With an average age of 63, many had already aged out of menopause symptoms like hot flashes or night sweats when they took part in the hormone therapy trial.

New data released this week by researchers in the UK widened the aperture, analyzing the effects of HRT on over 180,000 postmenopausal women — including many in their late 40s and early 50s.

Researchers at the University of East Anglia and the University of Exeter found that UK women who used HRT had a "modest" 10% lower risk of developing dementia, compared to their peers who didn't take hormones.

But timing really mattered. Women between the ages of 46 and 56 saw the best benefits. Older women saw, at best, no cognitive protection and potentially some harm.

The study shouldn't be taken as gospel, experts say. It's observational and lacks a placebo-controlled group, so more research will be needed to replicate the findings. Still, it demonstrates what experts have long thought is a key "window of opportunity" — the critical moment that may be the very best time for starting hormone therapy.

The consensus among experts is growing. I spoke with doctors and leading academics researching different aspects of women's health, from the heart to the brain, and found they all broadly agree that we should drop the idea that HRT is dangerous for women who are experiencing menopause symptoms.

Even lead investigators who've been running the Women's Health Initiative study from the get-go say it's time to let this old stigma go.

"In the Women's Health Initiative memory study, we actually did see findings consistent with a neutral effect — no harmful effect of hormone therapy among the women who were age 50 to 55 at the start," Dr. JoAnn Manson, who co-runs the Women's Health Initiative study, said. "It's all consistent with the timing hypothesis, that starting early, close to the onset of menopause, is preferable to starting later."

Why starting hormone therapy during middle   age may help protect the brain

Middle age may be the best time to start hormone therapy. Maskot/Getty Images

Why timing matters comes down to how our bodies work. Estrogen is essential for brain health in women and men, helping regulate memory and mood, and allowing cells to properly absorb and use energy.

When women go through menopause, estrogen levels fall off a cliff, contributing to hot flashes, mood swings, brain fog, and sleep disruptions. (In men, estrogen levels also decline with age, but more gradually.)

"That hot flash is a signal," Brinton, a leading expert on the aging female brain, said. "It's like: 'Are you going to give me estrogen? I need estrogen up here!'"

After a while, without any intervention, the body adapts to this new, low-estrogen state.

"What our data show thus far is that that brain is a very different brain, and in many respects, it is an infla...

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