Hormone replacement therapy (HRT) appears to reduce women's risk of developing dementia by 10%, according to the largest ever study of the treatment. Landmark research following 183,000 post-menopausal women in Britain for 13 years identified a "window of opportunity" for women to start taking HRT between the ages of 46 and 56.
Overall, women taking HRT for at least a year were 10% less likely to go on to develop dementia and 16% less likely to get Alzheimer's disease. The research, by the University of East Anglia (UEA) and the University of Exeter, appears to show which women can benefit from HRT and at what point in their lives.
Study findings on age and risk reduction
Researchers analysed health data on 183,450 women from the UK Biobank database. Over a 13-year period, 4,000 of them were diagnosed with dementia. Those who started HRT aged 46 to 50 had a 13% reduced risk of dementia, while those who started taking HRT when they were aged 51 to 56 saw a 23% reduced risk.
The strongest benefit was identified for women who took HRT after surgical menopause such as a hysterectomy. These women had a 26% lower risk of being diagnosed with dementia. Women with the gene variant APOE4 - a risk factor for Alzheimer's - who also took HRT, had a 13% reduced dementia risk.
Expert comment on the 'window of opportunity'
Study leader Professor Anne-Marie Minihane said: "Dementia affects millions of people worldwide, with women making up almost two-thirds of Alzheimer's disease cases, the main form of dementia. In addition to living longer, the reason behind the higher female prevalence is thought to be related to the effects of menopause on brain metabolism."
She added: "We wanted to better understand how HRT could prevent dementia and to assess if particular groups of women may respond differently. The protective association between HRT and dementia was not the same for all women."
Commenting on the study, Prof Aimee Spector, of University College London, said: "This supports the `window of opportunity' hypothesis, suggesting that HRT use during the menopause transition phase - where symptoms are typically more problematic - is important."
Implications for cognitive health
Prof Minihane said: "We also found that women whose bodies naturally produced less oestrogen over their lives - because they started their periods late or hit menopause early - seemed to get more help from HRT. Their risk of dementia was around 16% lower with HRT."
Prof David Llewellyn, from the University of Exeter Medical School, said: "These findings represent a significant step forward. Rather than asking simply whether HRT affects dementia risk, we've been able to identify which women are most likely to benefit, and when."
Prof Minihane added: "While HRT has long been prescribed primarily to relieve menopausal symptoms such as hot flushes and night sweats, this work suggests it may also play a role in long term cognitive health for some women."
