Timing Matters: Hormone Therapy Within Five Years Cuts Alzheimer’s Risk

Women face a higher risk of developing Alzheimer’s than men, particularly after menopause, when levels of the hormone oestrogen decline.

Beginning hormone replacement therapy (HRT) within five years of menopause may reduce the risk of Alzheimer’s disease, according to new research.

Women face a higher risk of developing Alzheimer’s than men, particularly after menopause, when levels of the hormone oestrogen decline. Oestrogen is known to regulate energy production and inflammation in the brain, so HRT has been investigated as a possible way to mitigate this risk. However, past studies have produced conflicting results.

To clarify, Fnu Vaibhav and colleagues at Pandit Bhagwat Dayal Sharma University of Health Sciences in India analysed data from 53 studies involving over 8.4 million post-menopausal individuals. Their findings, presented on 15 September at the American Neurological Association meeting in Maryland, highlight how age and timing of HRT may explain the discrepancies.

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In randomised-controlled trials, participants on HRT showed a 38% higher risk of developing Alzheimer’s. But observational studies suggested the opposite—a 22% lower risk. Vaibhav notes that most trial participants were aged 65 or older, while observational studies often involved younger women. Further analysis showed that women who began HRT within five years of menopause onset had a 32% reduced risk of Alzheimer’s.

Roberta Brinton at the University of Arizona explains that once oestrogen declines, the brain shifts to alternative energy sources, sometimes breaking down key compounds needed for function. If this shift has already occurred, HRT may no longer help.

Vaibhav stresses the need for clearer evidence: “Women might be missing out on the benefits, or they might be at risk of harm.”