According to the Centers for Disease Control and Prevention (CDC), physical activity is “one of the most important things you can do for your health”.
The CDC recommends that adults get at least 150 minutes of moderate-intensity physical activity, such as brisk walking, or 75 minutes of vigorous physical activity, such as running, each week, as well as doing muscle-strengthening activity at least twice a week.
This is a minimum — doing more exercise than this will give greater benefits.
Exercise benefits not only your physical health, but is good for your brain too. Several studies suggest that aerobic exercise — movement that increases your heart rate and increases blood flow — may improve cognitive performance, reduce the risk of developing dementia, and even alleviate some symptoms in people with dementia.
Now, a new systematic review suggests that when and why you exercise could impact your dementia risk.
The review, which is published in Lancet Public Health, found that leisure-time exercise was associated with a decreased risk of dementia, whereas physically demanding work was linked to an increased risk of developing the condition.
Steven Allder, MD, a consultant neurologist at Re:Cognition Health, who was not involved in this research, told Medical News Today:
“I think the findings are certainly worth paying attention to, particularly because the analysis included more than four million people and followed participants for many years. The consistency of the results across a large number of studies makes the association interesting and potentially important.”
“However,“ Allder cautioned, we need to be careful not to confuse an association with cause and effect. Because this was an observational study, we cannot say that occupational physical activity causes dementia or that leisure exercise directly prevents it.”
The international team of researchers that conducted this review, led by scientists at the University of Southern California, analyzed data from 74 studies with more than 4.2 million participants from 30 countries.
The participants ranged in age from 45 to 93 years at the start of the median 10-year follow-up. During follow-up, researchers recorded all diagnoses of all-cause dementia, Alzheimer’s disease, and vascular dementia.
All 74 studies assessed physical activity by self-reported questionnaires or objective measurements, and included comparison with a reference group — active versus inactive, low- versus high-activity. Occupational physical activity was recorded only for those in work, rather than non-working or retired.
People who engaged in leisure-time physical activity had a 24% decreased risk of developing dementia compared with those who were least active. Occupational physical activity, in contrast, was associated with a 20% increased risk of dementia.
Allder told MNT that leisure time physical activity may protect the brain in several different ways: “Regular exercise improves cardiovascular health and blood flow, helps control blood pressure, blood sugar and cholesterol, and may support the brain’s ability to maintain healthy connections between nerve cells.”
“There is also something distinctive about leisure activity,” he continued. “We choose to do it. “
“Going for a walk with a friend, swimming, cycling or playing a sport can combine physical activity with social interaction, enjoyment and mental stimulation. These factors may reduce stress and social isolation, while helping to build what we think of as cognitive resilience, which is the brain’s ability to cope with age-related changes,” Allder suggested
“So, it may not simply be about the amount of movement, but also the physical, psychological and social benefits that come with enjoyable, voluntary exercise,” he told us.
“It would be wrong to conclude that physically demanding work itself causes dementia,” Allder stressed.
The researchers found that higher levels of occupational physical activity were consistently associated with an increased risk of all-cause dementia in analyses adjusting for age, education and chronic disease.
They suggest that other factors involved in physically demanding jobs may play a role in increasing dementia risk. These factors could include heightened psychosocial stress, hazardous occupational exposures, and increased exposure to air and noise pollution, both of which have been linked to higher dementia risk.
Allder cautioned that the finding should be interpreted carefully, as the increased risk may reflect the context surrounding occupational activity.
“Someone in a physically demanding occupation may spend many hours standing, lifting, carrying or performing repetitive movements, often with limited control over the pace or intensity and not enough opportunity for recovery. Physically demanding jobs can also be associated with chronic stress, shift work, noise, air pollution and other workplace exposures,” he explained.
“There may also be a knock on effect,” he continued. “Someone who is physically exhausted after a demanding working day may have less time or energy for recreational exercise, social activities and other behaviours that support healthy ageing.”
Natan Feter, PhD, postdoctoral scholar and research associate at the University of Southern California, first author on the study, also advised caution when interpreting their results:
“We cannot completely rule out residual confounding — that is, the possibility that some of the association we observed is explained by factors we did not measure or fully account for. This is particularly important for occupational physical activity, because physically demanding jobs may cluster with other social, economic, environmental, and health-related disadvantages.”
“For this reason, our findings should not be interpreted as showing that physical activity at work itself causes dementia, but rather that the broader context in which that activity occurs may be important,” noted Feter.
“When promoting physical activity at the population level, we must ensure everyone has equal access to choice-led, safe, pleasant, and meaningful physical activity,” Feter told us.
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The study authors note that rather than simply encouraging people to “move more,” dementia prevention efforts should recognize that not all physical activity occurs under the same conditions.
“For me,” Allder commented, “the most important message is that people should not be discouraged from being physically active, including those who have physically demanding jobs.”
“Instead, this research reminds us that physical activity is more complicated than simply counting steps or hours of movement. The way we move, the environment in which we do it, whether we have control over it, whether we can recover afterwards and whether it is enjoyable and socially engaging may all matter,” he told MNT.
“It also reinforces the importance of making recreational exercise accessible to everyone. Walking, cycling, swimming, dancing or simply being active with friends can all be valuable,” added Allder.
“Ultimately, dementia prevention is likely to involve a combination of factors, including regular exercise, cardiovascular health, good sleep, social and mental engagement and addressing other modifiable risk factors, rather than any single behaviour in isolation.”
– Steven Allder, MD
