HRT can protect women against Alzheimer's – providing it is taken at the menopause, according to researchers.
A study showed women who began taking hormone replacement therapy within five years of the menopause cut their risk of the disease by a third.
But the findings suggest that if HRT is started in later life, it could give women a greater risk of developing the condition, leading some experts to believe there is a 'window of opportunity' when the benefits are maximised.
The study found that women who began HRT within five years of menopause had a 30 per cent lower risk of Alzheimer¿s dementia than those who had not used HRT
The researchers at Johns Hopkins University, in Baltimore, followed 1,768 women aged 65 and over for 11 years, recording a history of their HRT use and the date their menopause began.
A total of 1,105 women had used some form of hormone therapy, the report in journal Neurology noted.
During the study, 176 women developed Alzheimer's disease, including 87 of the women who had taken hormone therapy compared with 89 of the 663 who had not.
The study found that women who began HRT within five years of the menopause had a 30 per cent lower risk of Alzheimer's dementia than those who had not used HRT.
PATIENTS 'NOT DYING WHERE THEY WANT TO'
The risk was unchanged among other hormone users who began treatment more than five years after the menopause. And the protective effect was even larger in women using HRT for ten years or more.
But the risk of dementia among women who had started HRT when they were at least 65, which, depending on the individual, can be more than a decade after the menopause, was almost doubled.
The protective effect from HRT may come from boosting supplies of the hormone oestrogen, which is thought to play a key role in keeping the brain healthy, or the improvement in heart risk factors linked to HRT.
Earlier this month a study found HRT can reduce the risk of heart attacks and heart failure.
In the United Kingdom, women in their 50s are told to use HRT drugs short-term and for no longer than five years.
Dr Simon Ridley, head of research at Alzheimer's Research UK, said: 'Previous research into HRT has shown mixed results, but this useful study suggests the timing of hormone use may be critical for either raising or reducing the risk of Alzheimer's.
'More work is needed to understand this link and help women make informed decisions about whether to start HRT, but these findings could be important for guiding future research.
Read more: http://www.dailymail.co.uk/health/article-2222545/HRT-taken-menopause-protect-women-Alzheimers.html#ixzz2AKF4SpL2
Follow us: @MailOnline on Twitter | DailyMail on Facebook