Harvard Health Letter

Ask the doctor: Can exercising ward off Alzheimer's disease or dementia?

Q. Can exercising ward off Alzheimer's disease or dementia?

A. There is pretty strong evidence that regular exercise in people without dementia reduces (but does not eliminate) the risk of cognitive decline and dementia as we age. Several randomized clinical trials of regular exercise report a protective effect on cognitive function. When benefits from a particular behavior are reported, doctors tend to be more inclined to believe the result if they know of a biological mechanism that could explain it. Brain imaging has found somewhat larger volumes of brain tissue, particularly in the parts of the brain essential to memory, among people who exercise regularly.

It may come as an unpleasant surprise, but we share a lot of genes with rodents. That's why the results of experiments in rodents often prove to be true in humans. Rodents that exercise regularly, compared with those that don't, have increased amounts of a brain molecule called brain-derived neurotrophic factor (BDNF) that builds new brain cells. Exercising rodents also are less likely to have brain deposits of a molecule called beta-amyloid, which is found in abundance in the brains of people with Alzheimer's disease. Rodents that regularly exercise also solve mazes faster.

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