The UCLA study reports that people who are more sedentary have thinning in brain regions linked to memory—and even high-levels of exercise don’t seem to undo the effects of sitting too much.

The team looked at the connections between sitting, exercise, and the thickness of his or her medial temporal lobe, which is involved in memory formation, as well as its subregions. Participants, aged 45 to 75, answered questions about how much they’d sat on average over the past week and how much exercise they got at low, medium, and high intensities. Some physical measures were taken, and they were all tested for the “Alzheimer’s gene” variants (APOE). Finally, their brains were scanned with MRI to measure the thickness of regions in the medial temporal lobe.

As mentioned, time spent sitting was significantly correlated with less thickness in the medial temporal lobe, and certain areas within it, including the entorhinal cortex, the parahippocampal cortex, and the subiculum. Interestingly, exercise was not correlated with thickness in these regions, suggesting that exercise can’t undo the damage that excessive sitting brings. The authors write in their paper, “it is possible that sedentary behavior is a more significant predictor of brain structure, specifically [medial temporal lobe] thickness, and that physical activity, even at higher levels, is not sufficient to offset the harmful effects of sitting for extended periods of time.” There wasn’t a link between APOE status and thickness in the regions of interest.

Sedentary behavior is known to be a predictor of Alzheimer’s risk. In fact, the team points out that earlier studies have calculated that about 13% of Alzheimer’s cases may be due to inactivity, and that even a 25% reduction in sedentary behavior would reduce Alzheimer’s prevalence by about one million cases across the globe.

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