Hormone replacement therapy timing and individual health history shape dementia risk, according to a large prospective study of nearly 185,000 U.K. Biobank participants published in Alzheimer’s & Dementia. While the research links early initiation to lower risk, a separate World Health Organization-commissioned review finds no strong evidence that replenishing hormones after menopause is linked to dementia.
The debate surrounding menopause hormone therapy and its long-term effects on the brain has taken a significant turn, with two major evaluations reaching different conclusions about cognitive health. A massive prospective analysis of U.K. Biobank data suggests that starting hormone replacement therapy during the menopausal transition is tied to a reduced risk of dementia over more than a decade of follow-up. Yet a concurrent, sweeping systematic review commissioned by the World Health Organization found no strong evidence that the treatment impacts dementia risk one way or the other.
U.K. Biobank Findings Point to Timing and Specific Patient Groups
The observational study, led by researchers at the University of East Anglia and published in Alzheimer’s & Dementia, tracked 183,450 postmenopausal women for an average of 13.3 years. During the follow-up period, scientists identified 3,948 cases of dementia. The findings revealed that women who used hormone replacement therapy had a lower risk of all-cause dementia, with the strongest protective associations appearing among specific cohorts.
Timing emerged as a critical variable in the data. Women who started hormone replacement therapy between the ages of 46 and 50 saw a notable risk reduction, while those who initiated treatment between 51 and 56 experienced the greatest benefit.
Researchers also observed pronounced risk reductions in subgroups traditionally considered more vulnerable. Women who underwent surgical menopause, those who carried the APOE4 gene variant—the primary genetic risk factor for Alzheimer’s disease—and individuals with lower lifetime estrogen exposure all demonstrated lower dementia risks with hormone use. Prof Anne-Marie Minihane, director of the Norwich Institute for Healthy Ageing at the University of East Anglia, noted that the association is particularly striking for APOE4 carriers, who typically face higher baseline risks and fewer established prevention options.
“This is really important because Apoe4 carriers are typically considered at higher risk and have fewer established prevention options.”
Prof Anne-Marie Minihane, director of the Norwich Institute for Healthy Ageing at the University of East Anglia, via The Guardian
World Health Organization-Commissioned Review Reaches Cautious Conclusions
Contrasting sharply with the prospective Biobank findings, a systematic review commissioned by the World Health Organization found no strong evidence that replenishing hormones alters cognitive decline.
While the U.K. Most of the underlying research remains observational, meaning it cannot prove direct cause and effect.
Clinical Guidelines and Regulatory Shifts Amid Ongoing Debate
The new evaluations arrive during a period of transition for hormone therapy regulation and public perception. In the United States, hormone replacement therapy usage dropped steeply from 26.9% in 1999 to 4.7% in 2020, following early findings from the Women’s Health Initiative that linked combined hormone formulations to increased risks of heart disease and breast cancer in older women. However, the U.S. Food and Drug Administration removed black-box warnings in 2026.
Medical organizations maintain that hormone therapy is safe and effective when prescribed for menopausal symptoms in younger women or those within 10 years of menopause onset, but they caution against starting the medication solely to prevent cognitive decline.
Researchers stress that the upcoming release of the World Health Organization guidelines on reducing the risk of cognitive decline and dementia, expected in 2026, will incorporate these latest findings.
