Thursday, January 13

How does regular exercise protect against mental decline?

An old man playing basketball

Q. Is it true that regular exercise protects against mental deterioration as well as obesity, diabetes, and heart disease? If that's the case, how can exercise help with all of this?

A. For decades, we've got solid data that regular exercise protects against all of these things. But how do you do it? That has been the question. It's simple to understand how burning calories through regular exercise might help prevent weight gain. However, it's been more difficult to figure out how exercise can protect you from diabetes, heart disease, and dementia.

The Harvard Health Letter published an article in 2012 on a hormone named irisin that was discovered at Harvard Medical School (pronounced EYE-ris-in). The hormone was first discovered in mice, but it was later discovered in humans. Muscles and possibly other organs, including the brain, create irisin during exercise.

Experiments have shown that this molecule converts white fat cells (which store fat) to brown fat cells (which burn fat), as well as improves insulin resistance. These adjustments help people lose weight and protect them from diabetes and heart disease. Is irisin also responsible for the positive effects of exercise on the brain?

It may, according to a study published online by the journal Nature Metabolism on Aug. 20, 2021, by many of the same Harvard researchers. Blood levels of irisin were very low and brain cells (neurons) were aberrant when a gene required for the production of irisin was knocked out in mice from birth. Exercise did not boost brain function in these animals as it did in mice with an intact gene. This suggested that irisin may be to blame for the positive effects of exercise on the brain. To investigate this further, the researchers employed gene therapy to replace the knocked-out gene in mice with fresh copies of the healthy gene. When the mice exercised, they produced a lot of irisin, and their cognitive ability improved as a result.

The scientists next used gene therapy to increase irisin levels in animals with a condition similar to Alzheimer's disease. The mice's cognitive abilities improved, as did the brain abnormalities associated with Alzheimer's disease. Irisin may protect against Alzheimer's-like disease in the mouse brain by lowering brain inflammation, according to the study.

The lessons learned from mouse experiments are not necessarily transferable to people. The fact that humans and mice both share the same irisin molecule gives hope that the discovery of irisin will one day help human health. More broadly, this research suggests that one or more hormones produced by exercise may be responsible for the many distinct health benefits of regular exercise, at least in part.

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