How exercise may help keep your memory sharp

A HORMONE released during exercise may improve brain health and lessen the damage and memory loss that occur during dementia, a study finds.

The study, published last month in Nature Medicine, could help to explain how, at a molecular level, exercise protects our brains and possibly preserves memory and thinking skills.

But many questions remain about how exercise alters the inner workings of the brain. Those issues attracted an international consortium of scientists focused on preventing, treating and understanding Alzheimer’s disease.

Because Alzheimer’s is believed to involve, in part, changes in how brain cells use energy, the scientists reasoned that exercise might be helping to protect brains by increasing levels of the muscle-producing hormone irisin there. Tests revealed irisin in the brain, which might have been created in the brain itself.

The scientists used mice, some healthy, others bred to develop a rodent form of Alzheimer’s.

They infused the brains of the mice bred to have dementia with irisin. Those mice began to perform better on memory tests. They soaked the brains of the healthy mice with a substance that inhibits production of irisin, then pumped in the protein, beta amyloid, giving them dementia. Without irisin, the mice showed signs of worsening memory.

The scientists found that when they added irisin to healthy mice, gene expression changed in ways that would be expected to lessen damage from beta amyloid.

Finally, they had healthy mice work out. Beforehand, some of the mice were treated with the substance that blocks irisin production. In the untreated animals, irisin levels in the brain blossomed during the exercise and, later, after the animals’ brains were exposed to beta amyloid, they seemed to fight off its effects, performing much better. But the animals unable to create irisin did not benefit much from exercise.

These experiments suggest exercise may protect against dementia in part by triggering an increase of irisin, but can’t tell us if exercise and irisin will work similarly in people or whether exercise and irisin can prevent Alzheimer’s.

The scientists hope soon to test a pharmaceutical form of irisin as a treatment for dementia in animals and, eventually, people.