It's better to take the stairs instead of the elevator and go jogging a few times a week: Many people make sure they get enough exercise, and not just to stay physically in shape. You also want to be mentally fit and for as long as possible. Scientists have been reporting for a long time that exercise protects against dementia. The credo was: Every step counts. But a large study is now shaking this up: Apparently it's not just how much you move that counts - but also why and under what conditions. Leisure time exercise is associated with a lower risk of dementia. Physically strenuous work, on the other hand, has a higher rate. What's behind it?
This “physical activity paradox” is already known from cardiovascular research: those who work in construction do not have the same health benefits as someone who trains for a triathlon. In fact, hard workers are more likely to suffer a heart attack and die earlier, as large data analyzes from Denmark showed. However, this connection has not yet been broadly summarized for dementia.
The research team led by David Raichlen from the University of Southern California has now published a meta-analysis in the journal “The Lancet Public Health”. 74 studies with a total of more than 4.2 million people from 30 countries were included. The participants were between 45 and 93 years old and were followed for an average of ten years. The total number of people suffering from dementia as well as Alzheimer's and vascular dementia was recorded.
Those who exercised a lot in their free time had a 24 percent lower risk of dementia than those who exercised the least. This meant walking, cycling, jogging, swimming and other sports. Working in the garden or cleaning the house could also have a protective effect: housework was associated with a slightly lower risk of dementia, although this was only examined in one study. However, those who were physically active at work had a 20 percent increased risk.
"The results challenge the long-held assumption that 'every movement counts' when it comes to brain health," said study lead author Natan Feter of the University of Southern California.
But why does it make a difference to the brain whether you lift a load in the gym or on a construction site? The researchers cannot find a clear explanation. But there are various factors that could play a role, says neuroscientist Gerd Kempermann, who researches dementia at the German Center for Neurodegenerative Diseases in Dresden. “The context of the movement is crucial.” For example, stress probably plays a big role. “Physically demanding jobs often take place under high pressure,” says Kempermann. It is different whether you decide to achieve a better running time or whether someone else demands that you put away three more shelves.
In addition, there are possible stresses at work: noise, pollutants, heat, risk of injury, little recovery time. The study authors also suspect that it is not the exercise itself that is harmful, but rather the working conditions in physically demanding jobs.
Motivation also counts for Kempermann. When doing sports in your free time, you consciously decide to exercise. When it comes to physical work, however, it is a duty. “It’s also about the feeling of self-efficacy,” he says. How much can someone control when and how they engage in physical exertion? In physical jobs, however, you are often dependent on others, says Kempermann. However, much is still unclear and difficult to grasp.
It is important, however, that the studies only show associations but cannot prove a cause. Although other factors that influence the risk of illness, such as family history, were eliminated as best as possible, it cannot be completely ruled out that the result was influenced by people's lifestyle or level of education. For example, people who do physically demanding work eat less healthily on average. “The basic requirements are very different,” says Kempermann. Another limitation of many studies is that the level of physical work is often based on self-reports. But what that means at work or at home is often monitored less meticulously than on the treadmill. Even “physical work” in construction can mean completely different things, says Kempermann: building a roof structure, pouring asphalt, hauling stones or working as a painter.
You shouldn't avoid such physically demanding jobs, says Kempermann. But the data could have an impact on what advice is given to people in such jobs: “Even those who exercise a lot at work can benefit from exercise in their free time.”
