Signs of dementia may be detected as early as nine years before patients are diagnosed with the condition, new research suggests.
A University of Cambridge study reported 'subtle' impairments - from problem solving and number recall - are seen years before patients' dementia symptoms were clear enough to be diagnosed.
Researchers say their findings are a step toward screening at-risk patients and intervening at an earlier stage to reduce their chances of developing dementia-related diseases like Alzheimer's disease. Risk factors include being over 50, high blood pressure and not getting enough exercise.
"When we looked back at patients' histories, it became clear that they were showing some cognitive impairment several years before their symptoms became obvious enough to prompt a diagnosis," said the study's first author, Nol Swaddiwudhipong, a junior doctor at the University of Cambridge.
"The impairments were often subtle, but across a number of aspects of cognition.
"This is a step towards us being able to screen people who are at greatest risk – for example, people over 50 or those who have high blood pressure or do not do enough exercise – and intervene at an earlier stage to help them reduce their risk."
The findings could also help select those suitable for clinical trials for new treatments.
Senior author Dr Tim Rittman from the Department of Clinical Neurosciences at the University of Cambridge added: "People should not be unduly worried if, for example, they are not good at recalling numbers.
"Even some healthy individuals will naturally score better or worse than their peers.
"But we would encourage anyone who has any concerns or notices that their memory or recall is getting worse to speak to their GP."
He added: "The problem with clinical trials is that by necessity they often recruit patients with a diagnosis, but we know that by this point they are already some way down the road and their condition cannot be stopped.
"If we can find these individuals early enough, we'll have a better chance of seeing if the drugs are effective."
In the study published in Alzheimer's & Dementia: The Journal of the Alzheimer's Association, researchers analysed data from the UK Biobank database and found impairment in several areas, such as problem solving and number recall, across a range of conditions.
Currently there are very few effective treatments for dementia or other neurodegenerative diseases such as Parkinson's disease.
Experts suggest this is partly because these conditions are often only diagnosed once symptoms appear, whereas the underlying issue may have begun years – even decades – earlier.
This means that by the time patients take part in clinical trials, it could already be too late in the disease process to alter its course. Until now, it has been unclear whether it could be possible to detect changes in brain function before the onset of symptoms.
As well as collecting information on health and disease diagnoses, UK Biobank collected data from a range of tests including problem solving, memory, reaction times and grip strength, as well as data on weight loss and gain and on the number of falls experienced.
This allowed researchers to see whether any signs were present at baseline – when measurements were first collected between five and nine years before diagnosis.
People who went on to develop Alzheimer's scored more poorly compared with healthy individuals when it came to problem solving tasks, reaction times, remembering lists of numbers, prospective memory (our ability to remember to do something later on) and pair matching.
This was also the case for people who developed a rarer form of dementia known as frontotemporal dementia, the researchers found.
According to the study, people who went on to develop Alzheimer's were more likely than healthy adults to have had a fall in the previous 12 months.
Scientists found that for every condition studied – including Parkinson's disease and dementia with Lewy bodies – patients reported poorer overall health at the beginning.
The research was funded by the Medical Research Council with support from the NIHR Cambridge Biomedical Research Centre.
David Thomas, head of policy at Alzheimer's Research UK, said: "It is increasingly clear that the best chance to affect the course of the diseases which cause dementia lies in intervening at their earliest stages.
"Health services don't routinely offer the tests needed to detect changes in brain function that happen before symptoms are noticeable, like those alluded to in this study.
"In fact, the NHS is currently unable to guarantee early and accurate diagnosis for people living with dementia – more than a third of people over 65 living with dementia go undiagnosed.
He added: "It's now more important than ever that NHS services reflect our growing understanding of the importance of detection and early diagnosis.
"We must ensure that people with dementia don't fall through the cracks at a time when treatment or risk-reduction interventions are most likely to be effective."
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