Movement to movement: physical labor linked to risk of dementia

Physical activity is not always equally linked to brain health. People who moved a lot in their free time had a 24% lower relative risk of developing dementia than the least active participants. At the same time, high physical activity at work was associated with a 20% increase in the indicator. This is stated in an article published in The Lancet Public Health.

The Paradox of physical activity

The authors concluded that not only the duration and intensity of movement, but also its purpose may be important for brain health. Walking, swimming, or cycling in your free time takes place in a different physical and psychological context than weight lifting, prolonged standing, and repetitive activities at work.

A team led by David Raichlen, Professor of biological Sciences and anthropology at the University of Southern California, analyzed the results of 74 cohort studies and case–control studies. The total sample exceeded 4.2 million people aged 45 to 93 from 30 countries.

The median follow-up period was 10 years. During this time, the researchers tracked cases of all types of dementia, Alzheimer's disease, and vascular dementia. Instead of combining all movements into one indicator, the researchers divided activity into four categories: activities in their free time, physical activity at work, household chores, and active movement, such as walking or cycling.

Sport has been linked to reduced risk

Participants with the highest levels of leisure-time physical activity had a 24% lower relative risk of dementia than those in the least active group. These activities included walking, running, swimming, cycling, and various sports.

We are talking about the relative risk. The results obtained do not mean that exercising is guaranteed to prevent dementia in a particular person or reduce the absolute probability of the disease by exactly 24%.

Physical activity at home also showed a possible protective link. However, the corresponding result was obtained in only one study, so the authors considered the evidence base insufficient for confident conclusions.

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The opposite picture was found when analyzing the professional workload. People who performed physically demanding work had a 20% higher relative risk of dementia. A slight increase in the indicator was also observed with active commuting, but this part of the analysis included only two studies.

According to the first author of the work, Nathan Feter, an employee of the University of Southern California, the findings cast doubt on the widespread notion that any movement is beneficial for brain health, regardless of its context.

How is work different from training

The activity in their free time is usually chosen by the person himself. He can determine the duration and intensity of the lesson, stop when tired and set aside time for recovery. Walking and sports are also often accompanied by communication, positive emotions and a reduction in psychological stress.

Physical work takes place in different conditions. It can include repetitive actions, prolonged standing, uncomfortable postures, heavy lifting, and insufficient recovery time. Such a load often lasts for several hours in a row and does not stop when fatigue appears.

As leisure time activity increased, the risk of dementia gradually decreased, after which the positive relationship reached a plateau. An inverse nonlinear relationship was observed for professional workload: as it increased, the risk increased, and then also stabilized.

The authors consider it unlikely that the unfavorable relationship is explained by the movement itself. Physically demanding professions are more often combined with chronic stress, insufficient control over the work process, noise, air pollution and other harmful effects.

Such employees may have less time and energy to exercise after their shift. They may also have more limited access to safe parks, sports facilities, and medical care. Therefore, the revealed relationship may reflect not one circumstance, but a combination of socio-economic and professional factors.

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What the study proves

The authors emphasize that the results should not be interpreted as a recommendation to avoid physically active work. The meta-analysis was based primarily on observational studies that reveal a link, but do not prove that occupational stress directly causes dementia.

The association persisted after age, education level, and chronic diseases were taken into account. However, the researchers could not completely separate the impact of the movement from profession, income, working conditions, stress levels and cognitive load. In almost all the included works, the participants independently reported how much and how they were moving. Such responses depend on a person's memory and may not accurately reflect the actual duration and intensity of activity.

Most of the data also came from high-income countries. Meanwhile, the conditions of physical labor and the availability of sports in their free time may vary significantly depending on the region.

Lucrezia Moreno Royo, Professor of Pharmacology at CEU Cardenal Herrera University, drew attention to the possible mixing of factors. The division of professions into primarily physical and intellectual ones may simultaneously reflect differences in cognitive reserve, job content, and stress levels.

In her opinion, further research should jointly take into account physical activity, profession, intellectual load and psychological working conditions. Without this, it is impossible to determine which part of the risk is directly related to the movement.

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You can even sit in different ways.

The findings of the meta-analysis are consistent with other recent work by the same research group. In July, researchers compared different types of sedentary behavior in about 1,700 people. Participants who were on average 53 years old at the beginning of the study reported the frequency of watching TV and the duration of sitting at work. More than 20 years later, they underwent magnetic resonance imaging of the brain.

Frequent TV viewing in middle age was associated with a smaller volume of brain regions involved in memory formation, as well as a greater volume of white matter changes. People who spent a lot of time sitting at work, on the contrary, found a larger volume of some parts of the cortex and fewer changes in white matter.

These results also do not prove that working at a desk protects the brain, and watching TV directly leads to its structural changes. The scientists did not perform an MRI scan at the beginning of the follow-up, and information about sedentary behavior was obtained from questionnaires. Nevertheless, the work has again shown that not only the position of the body can be important, but also the occupation of a person at that time.

According to the authors, preventive recommendations should not be limited to a call to move more. Equally important may be access to safe parks and hiking trails, free time for training, full recovery after work and reduction of harmful industrial impacts.

The main conclusion of the study is not that physical labor is harmful, but that sport is guaranteed to prevent dementia. A meta-analysis shows that workload cannot be automatically equated with exercise, and the benefits of movement for the brain should be assessed along with the conditions in which it occurs.