Women taking hormone replacement therapy (HRT) in the long-term could have a small increased risk of Alzheimer’s disease, research suggests.
Experts behind the study said women should be warned of the potential impact of HRT, but the Royal College of GPs said the findings should not be a cause for alarm.
HRT is taken to relieve symptoms of the menopause such as hot flushes and night sweats and comes as tablets, gels, cream and patches.
While most experts believe it is a safe treatment, long-term use has been linked to a small increased risk of blood clots, breast and womb cancer.
For the new study, experts examined the use of HRT in 84,739 postmenopausal women in Finland diagnosed with Alzheimer’s disease between 1999 and 2013, and compared them with 84,739 postmenopausal women without Alzheimer’s.
Almost all of the women with Alzheimer’s (98.8%) were diagnosed when they were aged 60 or over. More than half (55.7%) were over 80 when they were diagnosed.
The researchers, led by the University of Helsinki, found that use of HRT was associated with a 9% to 17% increased risk of Alzheimer’s disease.
This would mean an extra nine to 18 cases of Alzheimer’s disease per year could be expected in 10,000 women between the ages of 70 and 80.
The findings related to long-term use, including women on HRT for over 10 years.
The study found no difference between women taking oestrogen-only HRT or combined HRT (oestrogen and progesterone).
Writing in the British Medical Journal (BMJ), the team concluded: “Even though the absolute risk increase for Alzheimer’s disease is small, our data should be implemented into information for present and future users of hormone therapy.”
Professor Helen Stokes-Lampard, chairwoman of the Royal College of GPs, said: “HRT can be of greatest benefit to many women who are suffering from some of the unpleasant side-effects of the menopause, such as hot flushes and night sweats – and there is a large body of evidence that shows it is an effective and safe treatment for most women.
“However, as with any medication there are risks and it’s important that women are aware of them so that they can make an informed decision, with their doctor, before starting treatment.”
She added: “To minimise any risk, best practice for most women is to prescribe the lowest possible dose of hormones for the shortest possible time in order to achieve satisfactory relief of symptoms.
“This new research shows an association with very long-term use of combined HRT but does not prove that there is a causal link.
“Nevertheless, it is a large, independent study and it is important that it is taken into account as clinical guidelines are updated and developed.
“We would urge patients not to be alarmed by this research – as the researchers state, any risk is extremely low – and if they are currently taking HRT, to continue doing so as prescribed by their doctor.
“If they are concerned, they should discuss this with their doctor at their next routine appointment.”
Dr James Pickett, head of research for the Alzheimer’s Society, said: “What is fascinating is how this study focuses on women – a hot topic in dementia research with twice as many women living with the condition.
“There are still many unanswered questions before we can fully understand risk particularly for women. But with one person developing symptoms of dementia every three minutes in the UK, this is an area our researchers are working hard on.
“This large and well-controlled study adds to a conflicting pool of evidence around the effect of hormone therapy on risk of developing dementia.
“In this case, some women on hormone therapy had a slight increased risk of Alzheimer’s, but this increase was so small it shouldn’t cause alarm or deter women from their prescribed treatment – particularly those taking it over a short period of time.”