A blood test can predict the risk of dementia in women up to 25 years before symptoms appear, researchers say.
Experts in the US found that higher levels of a protein called p-tau217 – which is linked to the brain changes seen in Alzheimer’s patients – were an accurate predictor of developing cognitive problems and dementia.
Women are twice as likely to develop dementia, but experts do not know why, and a new study of almost 2,800 women found warning signs could be detected decades before symptoms.
Researchers from the University of California San Diego examined data from 2,766 women in the Women’s Health Initiative Memory Study, which enrolled women aged 65 to 79 in the late 1990s and followed them for up to 25 years.
The study involved only female participants and none had signs of cognitive impairment at the start of the study.
Blood samples were analysed at the start of the trial and again years later to measure p-tau217.
Dr Aladdin Shadyab, first author on the study, said: “Our study suggests we may be able to identify women at elevated risk for dementia decades before symptoms emerge.
“That kind of long lead time opens the door to earlier prevention strategies and more targeted monitoring, rather than waiting until memory problems are already affecting daily life.
“Ultimately, the goal is not just prediction, but using that knowledge to delay or prevent dementia altogether.”
Dr Sheona Scales, the director of research at Alzheimer’s Research UK, said: “Women are twice as likely to be affected by dementia, but we do not understand why there is this difference.”
“This study adds to growing research exploring whether blood‑based biomarkers could identify who may be at higher risk of dementia decades before symptoms develop.”
During 25 years of follow-up, researchers noted the women who developed memory or thinking problems, including dementia.
Those who had higher levels of p-tau217 in their blood at the start of the study were much more likely to develop dementia later in life, they found.
As levels of the biomarker increased, so did dementia risk.
However, independent experts pointed out that while p-tau217 in blood is now well established to be a good marker of brain changes that occur early in Alzheimer’s disease, not everyone with such changes will go on to develop dementia.
The study also looked at the impact of HRT on risk of dementia, finding an association between p-tau 217 blood test levels with dementia in women who took oestrogen and progestin, but not those taking oestrogen alone.
Masud Husain, a professor of neurology at the University of Oxford, said: “This is an impressive study that uniquely has been able to analyse blood samples from women followed up for up to 25 years.
“The findings show that the level of p-tau 217 in the blood provides an index of the risk of developing dementia in the future.
“These results add further support for growing evidence that testing p-tau 217 in blood might be an important way to screen for people who are most at risk of dementia, years before a diagnosis is made.”
Michelle Dyson, the chief executive officer at the Alzheimer’s Society in the UK, said: “Blood tests could transform how dementia is diagnosed and research we’re funding aims to make a blood test routinely available on the NHS for symptomatic Alzheimer’s disease within the next few years.
“This study suggests that there may be a correlation for women between having a higher level of the p-tau 127 biomarker earlier in life with an increased risk of developing dementia 25 years later.
“These findings are promising, but of course more research is needed to understand whether early identification of biomarkers can affect whether people will go on to develop dementia later on.”
The study is published in JAMA Network Open.