Some fraction of aging in the brain is due to a reduced blood flow to brain tissue, and thus a reduced delivery of nutrients and oxygen to brain cells. Vascular aging reduces the density of capillary networks in tissue, and increases stiffness of blood vessels. Equally, a sedentary lifestyle - and, later, heart failure - reduces the ability of the heart to pump blood uphill to the brain. Structured exercise programs consistent demonstrate health benefits in older individuals, likely because near everyone in later life fails to undertake sufficient exercise. Here, researchers show that one of those benefits is an increased flow of blood to the brain, an outcome that should slow the progression of neurodegeneration to some degree.
As many as one-fifth of people age 65 and older have some level of mild cognitive impairment (MCI) - slight changes to the brain that affect memory, decision-making, or reasoning skills. In many cases, MCI progresses to dementia, including Alzheimer's disease. 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.
Researchers 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. In both programs, exercise physiologists supervised participants for the first four to six weeks, then had the patients record their exercises and wear a heart rate monitor during exercise.
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.