Eat the right foods. Exercise more. Sleep better. There is no shortage of advice for keeping the brain healthy. But the effects of these measures are often overstated, according to two brain researchers.
"What is good for cardiovascular health, mental health, social participation,and quality of life is often also good for the brain," says Anders Fjell. But when '45 per cent reduced dementia risk' is presented as if it applies to individuals, that is misleading.(Stock photo: Shutterstock / NTB)
How well your brain functions in old age is largely shaped by conditions early in life. Long before we have the ability to influence them.
"Measures aimed at preventing dementia later in life may have some effect, but their benefits are often oversold," says Anders Martin Fjell.
Together with Kristine Beate Walhovd, he studies the brain and how our cognitive abilities develop during childhood and change throughout life.
They have now written an article in the Journal of the Norwegian Psychological Association in which they challenge several widespread beliefs about brain health:
The risk of developing dementia can almost be halved through lifestyle changes.
Getting a lot of sleep is necessary for effective ‘brain cleansing.’
Higher education protects against cognitive decline and dementia.
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Research partners Kristine Walhovd and Anders Fjell believe there are three widespread myths about brain health. They discuss these in a new article(Photo: University of Oslo)
Myth 1: 45 per cent of cases can be prevented
Much attention is given to what people can do to prevent dementia. The Lancet Commission, for example, reviewed a large body of research and identified 14 risk factors associated with dementia.
"We can prevent or delay nearly half of all dementia cases by addressing 14 risk factors from childhood and throughout life," Geir Selbæk said in 2024. He is the research director at the Norwegian National Centre for Ageing and Health and contributed to the report.
Walhovd and Fjell believe there are good reasons to be sceptical about how such figures are interpreted.
First, the 45 per cent estimate represents a theoretical maximum. It assumes that all the risk factors are present. The researchers argue that this is not necessarily the case in the Norwegian population.
For most people, the potential benefit would therefore be considerably smaller.
Moreover, the estimate is based largely on observational studies. These studies can identify associations but do not establish cause and effect.
Risk factors such as hearing loss, depression, and physical inactivity may be early symptoms of dementia rather than causes of the disease, they write.
Not ideal studies
Other researchers nevertheless argue that such analyses should not be dismissed outright.
Bjørn Heine Strand, a senior researcher at the Norwegian Institute of Public Health, said in an earlierinterview with Science Norwaythat the Lancet Commission's work is based on the best available research.
"This is a theoretical puzzle assembled from a large amount of research. They have concluded that the evidence is strong enough to justify believing that causal links exist," he said.
He stresses that obtaining definitive evidence about the causes of dementia is extremely difficult.
"Ideally, we would follow the same people throughout their lives in randomised studies. That's almost impossible in practice. Therefore, we have to rely on observational studies," he said.
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Most vulnerable in childhood
Walhovd and Fjell also point out that these figures apply to populations, not individuals. This is often misunderstood.
A person's risk of developing dementia is largely determined by a foundation established early in life, according to the researchers.
Much of this comes down to genetics.
A common assumption in ageing research is that the brain becomes more vulnerable to influence as we grow older. But evidence increasingly suggests the opposite, the researchers write. The brain is more plastic and receptive early in life.
Several risk factors commonly highlighted as important in adulthood, such as substance use, appear to have a much greater impact when they occur during foetal development
Research suggests that individual differences in cognitive ability remain surprisingly stable throughout life.
The researchers point to an important Scottish study in which 11-year-olds took intelligence tests in the 1920s.
When the same individuals were tested again in their 70s, 80s, and 90s, those who had scored highly as children generally continued to score highly in their 80s.
Another widespread belief is that getting good sleep gives us a cleaner and healthier brain.
One popular theory holds that sleep clears waste products from the brain, including amyloid, a protein associated with Alzheimer’s disease.
This has contributed to a widespread belief that we need a lot of sleep for the brain to stay healthy, the researchers write.
But when they examined studies involving humans, they found the evidence to be surprisingly weak.
If long sleep were critical for maintaining brain health, we would expect people who sleep less to experience more brain shrinkage and memory problems, while those who sleep longer would preserve their brains better.
This is not what the research shows, Walhovd and Fjell write in the article.
On the contrary, several studies have found that people who sleep longer have a higher risk of cognitive decline and dementia.
One possible explanation is that excessive sleep may be a symptom of an underlying illness or depression rather than a cause of good brain health.
Myth 3: Education protects against dementia
A third belief discussed in the article is that higher education protects against dementia.
Walhovd and Fjell argue that the research does not consistently support this claim.
When researchers compare the brains of people with higher levels of education to those with less education, they find that the brain shrinks at the same rate.
The fact that people with higher education tend to receive a dementia diagnosis later may simply reflect that they start from a higher level of cognitive functioning and therefore take longer to reach the threshold for diagnosis.
Lifestyle still matters
The researchers emphasise that lifestyle in adulthood is not irrelevant.
"What is good for cardiovascular health, mental health, social participation, and quality of life is often also good for the brain," says Fjell.
But the benefits are often exaggerated, he tells Science Norway.
"Especially when population-level estimates such as '45 per cent reduction in dementia risk' are presented as though they apply to individuals," he says.
We never had the chance to choose
Fjell has previously expressed concern that people who develop dementia may blame themselves for not having lived the 'right' way.
But according to the researcher, the foundation for how our brain functions is established so early in life that we have had no opportunity to make those choices ourselves.
"Brain health is shaped by genetics, childhood conditions, education, health, environment, and social factors, not just by the choices people make in old age," he says.
For that reason, prevention should involve more than individual lifestyle advice.
"It's also about stable differences that are established early in life, during foetal development, childhood, adolescence, and young adulthood," he explains.
Valuable to offer advice
Martin Bystad is a psychologist and brain researcher and works as head of research at the University Hospital of North Norway.
He believes that Walhovd and Fjell make an important point in arguing that individual outcomes can differ greatly from average effects.
But that does not necessarily mean we should be hesitant to make recommendations, he says.
"Many health interventions are recommended precisely because they are likely to provide benefits at the population level, even though not every individual will benefit. It can be valuable to advise people about behaviours that are likely to improve their health, without necessarily putting a specific number on how much they reduce the risk," he says.
The main challenge is communicating the uncertainty in a way that neither promises too much nor undermines measures that may still be beneficial, according to Bystad.
