Do you spend a lot of time sitting down? A new study has found that excess sitting can actually shrink the part of your brain responsible for storing memories. Evidence from clinical trials, epidemiological and neuroscience research is mounting that physical exercise could be a promising way to delay the onset of dementia and Alzheimer’s disease.

Other studies have shown that too much sitting, just like smoking, increases the risk of heart disease, diabetes and premature death. It is also known that atrophy of the brain’s medial temporal lobe (MTL) occurs with aging, resulting in impaired episodic memory.

But the exact association between sedentary behavior and MTL health is still unclear. So researchers at UCLA wanted to see how sedentary behavior influences brain health, especially regions of the brain that are critical to memory formation.

Medial Temporal Lobe Thinning

35 people ages 45 to 75 were recruited for the study. People with a history of dementia, major psychiatric or neurologic disorders, alcohol or substance abuse, head trauma or systemic disease affecting brain function, or uncontrolled hypertension or cardiovascular disease were excluded.

They answered questions about their physical activity levels and the average number of hours per day they spent sitting over the previous week. This was done using the self-reported International Physical Activity Questionnaire modified for older adults (IPAQ-E).

[caption id=“attachment_95230” align=“aligncenter” width=“680”]Oblique coronal images are acquired to cover the long axis of the hippocampus Oblique coronal images are acquired to cover the long axis of the hippocampus.
Credit: Siddarth et al CC-BY[/caption]

Each person had a high-resolution MRI scan, which provided a detailed look at the medial temporal lobe, a brain region involved in the formation of new memories.

The researchers found that sedentary behavior is a significant predictor of thinning of the MTL and that physical activity, even at high levels, is insufficient to offset the harmful effects of sitting for extended periods.

Cause And Effect

This study does not prove that too much sitting causes thinner brain structures, but instead that more hours spent sitting are associated with thinner regions, researchers said. In addition, the researchers focused on the hours spent sitting, but did not ask participants if they took breaks during this time.

The researchers next hope to follow a group of people for a longer duration to determine if sitting causes the thinning and what role gender, race, and weight might play in brain health related to sitting. Reducing sedentary behavior may be a possible target for interventions designed to improve brain health in people at risk for Alzheimer’s disease, researchers said.

The findings do raise some unanswered questions.

“There may also be differences in the effect of various types of ‘sitting’ behaviors, and this is an area for further investigation. It is possible that there may be two distinct groups: mentally active sitting and mentally inactive sitting. In mentally active sitting, individuals may be attending to cognitive demanding tasks such as crossword puzzles, documentation, writing, or computer games. In mentally inactive sitting, individuals may be engaging in less demanding, passive tasks such as watching television or movies,"

the authors wrote.

The study recieved support from the National Institutes of Health, Department of Energy, the McLoughlin Gift Fund for Cognitive Health, the Larry L. Hillblom Foundation, Fran and Ray Stark Foundation Fund for Alzheimer’s Disease Research, Ahmanson Foundation, Lovelace Foundation, the Sence Foundation, the UCLA Claude Pepper Older Americans Independence Center funded by the National Institute on Aging, AFAR, the John A. Hartford Foundation and the Centers of Excellence National Program.

Siddarth P, Burggren AC, Eyre HA, Small GW, Merrill DA (2018) Sedentary behavior associated with reduced medial temporal lobe thickness in middle-aged and older adults PLoS ONE 13(4): e0195549.

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