Illustration: Fran Pulido/The Guardian
The idea was simple. Recruit hundreds of people in their 80s and 90s, equip them with fitness trackers, and monitor their physical activity. Then, when the participants died, collect their brains and examine the tissue. Is there evidence, lurking in the tissue, that exercise benefits the brain?
The results, from a 2022 collaboration between the University of California in San Francisco and the University of British Columbia, were striking. Physical exercise, late in life, seemed to protect the ageing connections between brain cells – the synapses where memories are made. The work, if backed up by further studies, could see exercise, and potentially drugs that mimic biochemical aspects of activity – prescribed to help slow the onset of dementia.
We know there is a 30%-80% reduced risk of dementia in people who exercise
“We know there is a 30%-80% reduced risk of dementia in people who exercise,” says Kaitlin Casaletto, the lead author on the study and an assistant professor in neurology at UCSF. “My question was, wouldn’t it be cool if we could figure out exactly how this is happening? If we could identify some of the mechanisms of exercise for brain health? These are potential therapeutic targets we can bottle.”
A small mountain of work has linked physical exercise to better brain health and lower risk of dementia in older age. One recent study of nearly 80,000 people in the UK found that the risk of dementia was halved in people who reached the goal of 10,000 steps a day. But much is still unclear. Part of the observed benefit could be down to people with healthier brains simply exercising more.
While there are definite benefits to be had from exercise – greater blood flow to the brain, better cardiovascular health, lower blood pressure, less obesity and diabetes – there is still plenty to nail down.
Dementia is the number one killer in the UK, with the disorder affecting about 900,000 people. Most cases, about two-thirds, are driven by Alzheimer’s disease, but it is far from the only cause. Other forms, namely vascular dementia, dementia with Lewy bodies, and frontotemporal dementia, arise from other processes.
Whatever the cause, the steady destruction of brain cells erodes memory, thinking, movement and personality. In old age, dementia can be several of these conditions at once.
Some of the highest rates of dementia are found in developed countries with older populations. In Germany, Italy and Japan, more than 20 in every 1,000 people have dementia compared with fewer than nine per 1,000 in proportionally younger countries including Mexico, Turkey and South Africa.
The UK sits in the middle. Indigenous groups in the Amazon have some of the lowest rates. In one recent study, researchers confirmed only six cases among 604 Bolivian Tsimane and Moseten people aged 60 and over, suggesting that lifelong physical activity and healthier preindustrial diets substantially reduce the risk.
Over the next three decades, global dementia is due to rise substantially, particularly in north Africa, the Middle East and eastern sub-Saharan Africa, where population growth and ageing will be among the driving forces.
But dementia is not inevitable, nor is it the reward for dodging other fatal conditions. Take all of the risk factors that we as individuals, or nations through their policies, might improve, and potentially 40% of cases could be prevented or delayed. We would not eradicate dementia, and many people who did everything to keep their brains healthy would still succumb to the disease…
By: Ian Sample Science editor
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