Not all physical activity is equalwhen it comes to protecting the brain from dementia. Where and why we move may matter more than most people realise
A large new review of studies published in The Lancet Public Health found that leisure-time physical activity – such as sport, dancing or going to the gym – was linked to a 24% lower risk of dementia. Housework was linked to a 15% lower risk, although this finding came from just one study
Occupational physical activity, on the other hand, was linked to a 20% increased risk of dementia
The study compiled data from 74 studies involving more than 4.2 million people in 30 countries, making it one of the largest studies of its kind
Brain protection is well established
Physical activity may protect the brain in several ways. It improves blood flow, helping to deliver oxygen and nutrients to the brain. It also causes muscles to release molecules that can reduce inflammation, help the brain use energy and encourage the growth of new brain cells
That is one reason why reducing physical inactivity is a key part of the World Health Organization’s recently updated dementia prevention guidelines
There is plenty of evidence that being active can help protect against dementia. A UK Biobank study tracked people’s activity using wearable devices for four years. Even less than 35 minutes of moderate-to-vigorous activity a week was linked to a 41% lower risk of dementia compared with no such activity
More vigorous exercise – the kind that leaves you too breathless to talk – was linked to a 63% lower risk of dementia compared with being inactive
Meanwhile, the English Longitudinal Study of Ageing followed people for 17 years and found that the more active people were, the lower their risk of dementia. The most active group had about half the risk of the least active group
Walking outdoors – even as little as two miles a day – and gardening have also both been linked to a 25 to 36% lower risk of dementia
But the new Lancet study suggests that physical activity at work or while travelling to work may not offer the same protection. It may even be linked to a higher risk of developing dementia
Physical activity paradox
Physical activity at work, based on the combined data from five studies, was linked to a 20% higher risk. And active commuting, such as walking or cycling, based on just two studies, was linked to a 10% higher risk
Researchers call this the “physical activity paradox”. It is well documented in heart disease research: physical activity at work fails to deliver the same protective effect as the same activity done during leisure time, and can sometimes increase risk instead. Several explanations have been proposed
People in physically demanding jobs may have had fewer opportunities for education than people in office jobs. Education and mentally stimulating activities throughout life are linked to greater reserve capacity in the brain – its ability to cope with damage and keep working normally
Manual workers may also be more likely to work in polluted environments, such as factories or building sites. And commuting, particularly by bicycle or on foot, can mean greater exposure to air pollution. Air pollution has separately been linked to a higher risk of Alzheimer’s disease
About the author
Eef Hogervorst is a Professor of Biological Psychology, Loughborough University. This article was first published by The Conversation and is republished under a Creative Commons licence. Read the original article
Recreational exercise accounts for just 4% of active time in low-income countries, but 28% in high- and middle-income countries. So differences in income may shape the factors that influence dementia risk around the world
The researchers say more research is needed, particularly in low-income countries, to understand what is behind the link between physical activity at work and dementia
Not all physically demanding jobs are the same. Two physically demanding jobs can involve similar amounts of activity but very different exposures to noise, pollution, stress, heat and other hazards
These findings point to a deeper inequality: leisure time itself is a reuntries and those who do physically demanding jobs often have the least opportunity for the kind of activity that seems to protect the brain, while facing the working conditions that may undermine it. Understanding and addressing that imbalance may matter as much for dementia prevention as encouraging people to move more
