Scientists have previously shown that lower-than-usual levels of blood flow to the brain, and stiffer blood vessels leading to the brain, are associated with MCI and dementia. Studies have also suggested that regular aerobic exercise may help improve cognition and memory in healthy older adults. However, scientists have not established whether there is a direct link between exercise, stiffer blood vessels, and brain blood flow.

In the study, Zhang, Cullum, and their colleagues followed 70 men and women aged 55 to 80 who had been diagnosed with MCI. Participants underwent cognitive exams, fitness tests, and brain magnetic resonance imaging (MRI) scans. Then they were randomly assigned to either follow a moderate aerobic exercise program or a stretching program for one year. The exercise program involved three to five exercise sessions a week, each with 30-40 minutes of moderate exercise such as a brisk walk.

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Forty-eight study participants -- 29 in the stretching group and 19 in the aerobic exercise group -- completed the full year of training and returned for follow-up tests. Among them, those who performed aerobic exercise showed decreased stiffness of blood vessels in their neck and increased overall blood flow to the brain. The more their oxygen consumption (one marker of aerobic fitness) increased, the greater the changes to the blood vessel stiffness and brain blood flow. Changes in these measurements were not found among people who followed the stretching program.

Having physiological findings like this can also be useful for physicians when they talk to their patients about the benefits of exercise," says Zhang. "We now know, based on a randomized, controlled trial, that exercise can increase blood flow to the brain, which is a good thing.