Physical exercise is one of the few proven ways to maintain brain size and functioning into older age, say the researchers behind an analysis of 14 studies on exercise and brain health.

Activity is well-known to improve physical and mental health. From cardiovascular, metabolic and bone health, to depression and anxiety, regular exercise provides a positive step towards prevention and improvement of many chronic conditions.

Exercise prevented the decrease in hippocampal volume that is typically seen with aging.

The study looked at the impact of aerobic exercise on the brain's hippocampus. This region in the brain, named for its seahorse-like shape, is primarily involved in memory and in spatial navigation. It is one of the first brain areas damaged in Alzheimer's disease, and decreases in neuronal mass in most people during healthy aging, a change that is associated with cognitive decline.

This connection between exercise and hippocampal size has been investigated in rodents, where exercise has been found to cause new neurons to develop and prevent age-related decline in this portion of the rat brain. The research has been less clear in humans.

The team reviewed studies that involved over 730 adults, ages 24 to 76, who participated in a structured program of aerobic exercise, such as stationary cycling, treadmill use or walking. The exercise programs ranged from three to 24 months and involved two to five sessions per week.

People in the studies had a variety of clinical diagnoses at the time of assessment, including normal health, schizophrenia, depression and cognitive impairment. The volume of the hippocampus was measured by magnetic resonance imaging and compared to control subjects who did not participate in a structured exercise program.

Studies of healthy adults (690 subjects) showed a significant positive effect on the left region of the hippocampus when compared to controls, though the exercise interventions did not change the overall hippocampal volume. As lead author, Joseph Firth, explained, “Our data showed that, rather than actually increasing the size of the hippocampus per se, the main ‘brain benefits’ are due to aerobic exercise slowing down the deterioration in brain size. In other words, exercise can be seen as a maintenance program for the brain.”

This effect was not seen in studies of adults with schizophrenia, mild cognitive impairment, Alzheimer's and depression.

The positive effect of aerobic exercise on the hippocampus may be the result of the increased activity of brain-derived neurotropic factor (BDNF), a growth supporter for brain cells, the researchers suggest. They conclude that, while more study is necessary, their analysis adds to the growing body of information that highlights the positive role of aerobic exercise in maintaining brain health and cognitive function.

The study is published in NeuroImage .