“Measures aimed at preventing dementia later in life may have some effect, but their benefits are often oversold,” researcher Anders Martin Fjell recently told Science Norway.
He and Kristine Beate Walhovd recently wrote an article in the Journal of the Norwegian Psychological Association in which they challenge several myths about brain health.
One of these myths is that the risk of dementia can almost be cut in half through lifestyle changes.
The figure comes from the Lancet Commission’s work on dementia prevention, intervention, and care.
Geir Selbæk is director of research at the Norwegian National Centre for Ageing and Health and one of the contributors to the Lancet report.
“There is strong evidence that lifestyle- and health-related measures can help reduce the risk of dementia. However, the size of the effect for any individual remains uncertain,” he writes in an email to Science Norway.
Must be cautious about how the message is communicated
In its 2024 report, the commission concluded that around 45 per cent of dementia cases in the population could potentially be prevented by reducing 14 risk factors.
Researchers Walhovd and Fjell argue that there are good reasons to be sceptical about how such figures are interpreted.
They point out that the 45 per cent figure is a theoretical maximum. It assumes that all the risk factors are present, which is not necessarily the case in the Norwegian population. Furthermore, the calculations are largely based on observational studies, which cannot establish cause and effect.
The researchers emphasise that lifestyle in adulthood does matter. But the effects are often “oversold,” Fjell told Science Norway.
“Especially when population-level estimates such as ’45 per cent reduction in dementia risk’ are presented as though they apply to individuals.”
Geir Selbæk agrees that it is incorrect to apply the figure of a 45 per cent reduction in risk to individuals. This applies more generally to health and lifestyle advice.
“Overall, one must be cautious when communicating this so that the message does not lead to increased stress, anxiety, depression, or shame, and thereby poorer health,” says Selbæk.
“At the same time, we must acknowledge that there is considerable public interest in disease risk in general, and perhaps cognitive decline and dementia risk in particular,” he adds.
Applies at the population level
Selbæk explains what lies behind the calculation.
“The 45 per cent figure is a theoretical estimate based on a model that combines the strength of the association between each risk factor and dementia risk and how common the risk factor is, while also adjusting for overlap between the factors,” he says.
This applies at the population level, which is also noted by the Lancet Commission, according to Selbæk.
“It directs the message towards policymakers and healthcare professionals. It is unrealistic to eliminate all of these risk factors entirely, but the message that public health measures can substantially influence the occurrence of dementia still stands,” he says.
Most people do not have all the risk factors
The 45 per cent figure assumes the presence of all the risk factors, Walhovd and Fjell write in their article.
In Norway, for example, fewer than two per cent of people consume more than 21 units of alcohol per week, around seven per cent smoke daily, and around six per cent have diabetes.
‘For most individuals, the theoretical ‘maximum benefit’ will therefore be only a fraction of 45 per cent, simply because they do not have these risk factors,’ the two researchers write.
The Lancet Commission produces an estimate that applies internationally, says Selbæk.
“There will be variations in risk profiles between countries, particularly regarding smoking rates and access to education. As mentioned, this figure cannot be transferred to each individual’s risk,” he says.
Nevertheless, Selbæk says the Lancet Commission’s summary can be an important tool for healthcare professionals providing advice on preventive health measures.
It would be unethical to conduct long-term experiments
The estimates are largely based on observational studies, write Walhovd and Fjell.
‘Such data is important, but it is very difficult to distinguish cause from effect,’ they write in the journal. ‘Hearing loss, depression, or physical inactivity, for example, may be early symptoms of – or consequences of – the same disease process that later leads to dementia, rather than independent causes.’
This is a well-known limitation that all researchers in this field are aware of and account for to varying degrees, says Geir Selbæk.
“For most of these risk factors, it would be unthinkable to conduct randomised controlled studies because the time between exposure to the risk factor and outcomes such as dementia is so long,” he says.
He notes that it would be extremely demanding in terms of resources and ethically highly problematic.
“For that reason, researchers have to rely on studies with a lower level of evidence. This means that multiple well-conducted studies must point in the same direction and that there must be plausible mechanisms explaining the associations,” he says.
The Lancet Commission, along with other literature reviews, have brought together these studies and assessed whether the overall body of evidence is sufficient to draw reliable conclusions, says Selbæk.
A well-known issue
Could it be that some of what appears to be risk factors are actually early symptoms of dementia?
“The issue of the direction of the association is well known and is especially relevant because dementia diseases, such as Alzheimer’s disease, begin in the brain many years before symptoms appear,” says Selbæk. “We have published a great deal of research showing that the direction of the association can reverse as the time of a dementia diagnosis approaches.”
He explains that high blood pressure in midlife, for example, is a clear risk factor for developing dementia later on, whereas among people who are in the process of developing dementia, low blood pressure is associated with increased risk.
“This is probably because the disease process itself affects blood pressure. Timing is critically important when evaluating risk profiles for dementia,” he says.
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Translated by Alette Bjordal Gjellesvik
Read the Norwegian version of this article on forskning.no
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