Review of 61 Mendelian randomization studies finds no clear genetic link of activity to depression

A systematic review of 61 studies that used Mendelian randomization (MR) has questioned the view that physical activity reliably protects against mental disorders, according to pravda.ru. The authors did not find clear genetic evidence that a high level of activity directly protects against depression, schizophrenia or anxiety disorders pravda.rupravda.rupravda.ruOpen source ↗. The results for general activity were contradictory.

MR uses genetic data to look for cause-and-effect relationships. It avoids errors typical of ordinary observational surveys, for example when a person moves more not because exercise helps but because they already feel better. Mental disorders such as depression and anxiety affect about 30% of people during their lifetime, and physical activity is a central part of the search for ways to prevent them.

Fitness measures and sedentary time

The data were more consistent for physical fitness indicators, such as grip strength and muscle mass. According to the authors, good fitness and muscle strength are more often associated with better cognitive function and mental state. Long periods of sitting are linked to mental health risks, but the association is often more complex than it appears. It is frequently explained by body mass index and socioeconomic status.

Why genetic and conventional studies differ

The authors name several reasons for the mismatch with conventional fitness research. Randomized clinical trials show how exercise affects a patient's condition at a given time, while genetic studies assess a lifelong predisposition to a certain level of activity pravda.rupravda.rupravda.ruOpen source ↗. Observational studies often confuse cause and effect: a person with depression may be less active because of the illness itself rather than a lack of exercise. Self-reported training volume also often differs from objective tracker data.

The researchers stress that the absence of a direct genetic link does not mean sport is useless. Accumulated data indicate that physical fitness, which objectively reflects the state of the body, has a positive effect on the brain. However, there is no simple universal remedy in the form of training. The authors recommend combining physical activity with other health-maintenance methods and taking individual characteristics into account. In their view, future studies should rely on triangulation, using several data-verification methods at once.