There are plenty of reasons out there to move your body more: to better your posture, to build strength, to improve flexibility, to boost your brain health, to reduce your risk for a myriad of diseases (such as heart disease, diabetes, and cancer). The list goes on.

You’d be hard-pressed to find a reason not to get off your butt, considering our sedentary lifestyles have been linked to obesity, anxiety and depression, cardiovascular disease, high blood pressure, and more. (“Sitting is the new smoking,” they say.) And if all that wasn’t scary enough, a recent study published in the journal PLOS One has identified a truly terrifying potential impact of inactivity: the thinning of the part of our brain responsible for creating new memories, called the medial temporal lobe (MTL).

The thinning of the MTL, which tends to occur with age, leads to issues with memory seen in many older adults. While previous research had already suggested a connection between fitness and a larger hippocampus (part of the MTL), none had explored the flip-side, a correlation between sitting more and a thinner MTL.

That’s where this study comes in. Researchers from the University of California surveyed 35 adults between the ages of 45 and 75 about their level of physical activity and the average number of hours they spent sitting in one place for an extended period of time per day. Then, they used a high-resolution MRI scan to take a detailed look at the volume of the participants’ medial temporal lobes to identify any possible correlations between the participants’ patterns of sitting and activity and the thickness of their MTL.

The results were pretty alarming. “We found that time spent sitting was associated with less thickness in the MTL and its sub-regions, in spite of physical activity,” says Prabha Siddarth, Ph.D., lead study author, of UCLA’s Semel Institute for Neuroscience and Human Behavior. This seems to indicate that sedentary behavior is a significant predictor of brain structure—specifically medial temporal lobe thickness—and that even high levels of physical activity can’t offset the harmful effects of sitting for extended periods of time.

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While the study is small, the connection it’s made between physical inactivity and the development of brain dysfunction deserves the bulging-eyes reaction it incurs—especially given the number of people worldwide who now have jobs that require them to remain stationary for extended periods of time.

“This was an associational study, so it does not prove that too much sitting undermines brain health—only that more hours spent sitting is linked to thinner brain structures,” says Prahba. “We would like to conduct a longitudinal [long-term] study and study participants over time to examine if sitting causes the thinning.”

Initial studies like this one, however, are still critical, because they develop the early data that establishes the need for studies that can determine causality, so the the appropriate interventions and treatments can be identified, explains Jesse Corry, M.D., stroke neurologist with Allina Health in St. Paul, Minnesota.

If you’re one of the estimated 13 percent of people who works a sedentary job, consider this study one more reason to incorporate physical activity into your day whenever possible. “This could include taking breaks from sitting during the day to go for short walks, and avoiding sitting for prolonged periods when you’re not at work,” suggests says Siddharth Sehgal, M.D., lead study author, Director of the Stroke Program at Tallahassee Memorial, and neurologist at TMH Physician Partners Neurology Specialists. “Everyone should try to participate in regular physical exercise several times a week to improve their chances of normal, healthy cognitive aging.”