Alzheimer’s disease is more widespread in people above the age of 85 than previously thought, a pioneering study has suggested.
Researchers used a simple blood test to search for biomarkers associated with the development of dementia.
The study also found more than one in 10 people over the age of 70 would meet the criteria for drugs that can slow down the early stages of Alzheimer’s.
Researchers at King’s College London, University of Gothenburg and Stavanger University Hospital analysed 11,486 blood samples provided by people over the age of 57 taking part in the Trondelag Health Study (HUNT) in Norway.
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They looked for how regularly proteins in the blood that have been linked to cognitive impairment came up, or the gradual deterioration in thinking, memory and reasoning.
The frequency of Alzheimer’s disease neuropathological changes (ADNC) – deposits of proteins in the brain that lead to the death of nerve cells – grew with age, according to the analysis.
The study found it was higher in older people, but lower than previously estimated in the younger groups.
ADNC was present in fewer than 8% of those aged 65-69, jumping to 65.2% in patients over the age of 90.
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In people over 70, the study found 10% had symptomless pre-clinical Alzheimer’s disease, while 9.8% had Alzheimer’s dementia.
Some 10.4% had prodromal Alzheimer’s, the stage between pre-clinical and dementia, when memory and thinking problems due to cognitive impairment are noticeable.
Researchers suggest 11% of the over-70s group would be eligible for antibody treatments, which slow down the early stages of Alzheimer’s.
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These drugs include lecanemab and donanemab, which are licensed for UK use but will not be made available on the NHS after the spending watchdog argued their benefits are “too small” to justify the cost.
Researchers also found ADNC “was more prevalent in individuals with lower education”.
Dr Richard Oakley, associate director of research and innovation at Alzheimer’s Society, said: “This is the first time we’ve seen this type of data from such a large group of people, with over 11,000 blood samples analysed.
“It is a stark reminder of the scale of dementia. We already know it’s the UK’s biggest killer, but its impact may be even bigger than we think.”
He added: “Blood tests could transform how Alzheimer’s disease is diagnosed. They are quicker, cheaper and can be easier for patients than scans or lumbar punctures. Ultimately, these tests could help many more people get a diagnosis earlier.”
Blood tests to diagnose Alzheimer’s are also not available on the NHS.
Doctors currently use lumbar punctures or PET scans to test for ADNC.
But a trial announced in September will recruit 1,100 people from memory clinics to investigate how well a blood test works on the health service, with results expected in three years.
Dag Aarsland, a professor of old age psychiatry at King’s Institute of Psychiatry, Psychology & Neuroscience (IoPPN), said of the Trondelag Health Study findings: “If we are to meet this global challenge, it is vital that we are able to detect signs of dementia at the earliest possible stages.
“This blood test looks to be an effective means of providing that clarity at scale.”
