Numerous studies in recent years have found a strong link between too much sedentary behavior and higher risks of heart disease and other health problems. One study found that sitting for long periods is also associated with thinning in regions of the brain that are critical to memory formation.

In the study, researchers questioned 35 men and women about their physical activity levels and the average numbers of hours a day they spent sitting during the previous week. Each study participant then had a high-resolution magnetic resonance imaging (MRI) scan. The scans provided researchers a detailed view of the medial temporal lobe (MTL), a brain region involved in the formation of new memories.

Results showed that the people in the study who spent the most time sitting tended to have more thinning in the MTL. Researchers also found that while sedentary behavior is a significant predictor of MTL, physical activity—even at high levels—is insufficient to offset the harmful effects of sitting for extended periods. The study did not prove that too much sitting actually causes thinner brain structures, but that there is a strong association.

One limitation of the study, aside from it including just 35 people, was that researchers did not explore if, or how often, the participants took breaks from sitting. In the future, the researchers hope to follow a larger group for a longer period of time and to study whether gender, race and weight. While there is no set number of hours that is considered safe or unsafe, health experts agree that it is best to reduce the number of hours you sit each day and take frequent breaks during long stretches when you’re seated.

This article originally appeared in Mind, Mood & Memory, a publication of the Department of Psychiatry at Massachusetts General Hospital, dedicated to maintaining mental fitness for middle age and beyond.

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