A new study has linked the use of hormone replacement therapy (HRT) with an increased risk of dementia – but experts are cautioning that solid conclusions cannot be drawn from the analysis, as its findings are correlational, not necessarily causal.
Danish scientists worked on the research, which was published in the British Medical Journal (BMJ). They surveyed data from 61,000 women in the Scandinavian country, with an average age of 70.
The women's health records were analysed to identify those who had been prescribed HRT after age 45. Researchers found that those who had taken the medication were 24% more likely to go on to develop dementia or Alzheimer's disease than those who did not.
During the perimenopause, a drop in the production of oestrogen and progesterone by the ovaries can trigger symptoms including brain fog, weight gain, vaginal dryness and unmanageable moods. HRT can re-fuel hormone levels to reduce the severity of symptoms
The longer that women took the medication, the more likely they were to develop dementia, the research found. The increase in risk went from 21% for those using HRT for less than a year to 74% for those on it for 12 years or more.
What are the limitations of this study?
If you take HRT, this might sound alarming. Academics not involved in the research, though, are stressing that this is an observational study, which means that individuals are observed without a treatment or any sort of intervention being given.
It means that the findings drawn are correlational and not necessarily causal – in short, there could be other reasons why the women with dementia ended up with the diagnosis, outside of taking HRT.
'This new piece of research uses data from a large number of women, and the statistical methods used are appropriate. But it can’t avoid some important limitations of this type of research,' says Kevin McConway, Emeritus Professor of Applied Statistics at The Open University.
'The researchers did find evidence that the chance of having a dementia diagnosis was greater in women who had previously used menopausal hormone therapy, and indeed found more detail on how the chance of dementia varied depending on how long women took the therapy, which type of dementia was involved, and other things.
'But, because the study was observational, it cannot establish that the higher chance of dementia was actually caused by using the hormone therapy.'
Why else could women be at higher risk of dementia?
David Curtis, Honorary Professor at the University College London Genetics Institute says: 'The authors of the editorial [an analysis of the study published alongside it] suggest a number of reasons for the observed association [between taking HRT and an increased risk of dementia].
'One of these is that women taking HRT would see doctors more often and hence be more likely to be diagnosed with dementia earlier. An even more convincing suggestion is that some women were actually prescribed HRT because they had memory problems. (There was an idea that women going through the menopause who had memory problems and similar symptoms might have these alleviated by HRT.)'
'It is typical that people who will eventually develop dementia will have mild memory problems years before they receive a formal diagnosis. So the editorial is really saying that women who eventually develop dementia may be more likely to be prescribed HRT in the years before they are diagnosed.'
There are other factors which the study did not investigate which could explain why the women who ended up with dementia were at increased risk.
'[This study] doesn’t provide a conclusive answer on whether HRT contributes to dementia risk, because the study did not consider some of the other factors known to be involved, such as social isolation, smoking or dietary factors like alcohol,' says Dr Susan Kohlhaas, Executive Director of Research & Partnerships at Alzheimer’s Research UK.
Women are at a greater risk of dementia than men. Coming to firmer conclusions about why this is should be a research priority, she adds. 'Dementia is the number one cause of death amongst women in the UK.'
'It affects about twice as many women compared with men, and this difference can’t be explained by differences in longevity alone. It’s therefore important to understand what contributes to dementia risk, as this could help develop prevention strategies for those most at risk in the future.'
'Understanding whether HRT plays a role in dementia risk has been a priority for the research community in recent years. Such studies, however, have so far been inconclusive and contradictory, with some suggesting that HRT reduces risk of dementia, and others suggesting it increases risk. Reasons for this may be because of differences in age when HRT is given, differences in how HRT is used, and different types of HRT used over the years.
I take HRT. What should I do now?
The experts commenting on this study are clear that further research in this area is very much needed, but that this study's findings should not influence your decision on whether to take HRT or not.
Keen to talk the potential pros and cons of the medication through with someone? 'People should speak to a qualified healthcare professional if they would like to know more about the known benefits and risks of taking HRT to manage symptoms of the menopause,' is Dr Kohlhaas' advice.
Claudia is Health + Wellness Director at Women's Health and Men's Health. She commissions, edits and writes about topics including the happiness potential of less conventional relationships, what the latest wave of psychedelic research means for women and how to thrive through each stage of your life. She regularly hosts and participates in panel talks about how we live now and is frequently asked to provide expert comment for national radio.
