In a first-of-its-kind international collaboration, researchers from Australia's National Institute of Complementary Medicine at Western Sydney University, as well as the UK's Division of Psychology and Mental Health at the University of Manchester, examined the effects of aerobic exercise on the hippocampus, which is critical for memory and other brain functions.
Brain health decreases with age, with the average brain shrinking by approximately 5% every decade after the age of 40.
Studies on mice and rats have consistently shown that physical exercise increases the size of the hippocampus, but until now, evidence in humans has been inconsistent.
The researchers systematically reviewed 14 clinical trials that examined the brain scans of 737 people before and after aerobic exercise programmes, or in control conditions.
The participants included a mix of healthy adults, people with cognitive impairment such as Alzheimer's, and people with a clinical diagnosis of mental illness, including depression and schizophrenia. Ages ranged from 24 to 76, with an average age of 66.
The researchers examined the effects of aerobic exercise on the subjects, including stationary cycling, walking, and treadmill running. The length of the interventions ranged from three to 24 months, with two to five sessions per week.
Overall, the results — published in the journal NeuroImage — showed that, while exercise had no effect on total hippocampal volume, it did significantly increase the size of the left region of the hippocampus in humans.
The paper stated: "A systematic search identified 4,398 articles, of which 14 were eligible for inclusion in the primary analysis.
"Post-hoc analyses indicated effects were driven through exercise, preventing the volumetric decreases which occur over time. These results provide meta-analytic evidence for exercise-induced volumetric retention in the left hippocampus."
Lead author and NICM postdoctoral research fellow Joseph Firth said the study provided some of the most definitive evidence to date on the benefits of exercise for brain health.
"When you exercise, you produce a chemical called brain-derived neurotrophic factor (BDNF), which may help to prevent age-related decline by reducing the deterioration of the brain," he said.
"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 programme for the brain."
Firth said along with improving regular 'healthy' ageing, the results had implications for the prevention of ageing-related neurodegenerative disorders such as Alzheimer’s and dementia. However, further research is needed to establish this.
Volume 166, 1 February 2018, pages 230 — 238
"Effects of aerobic exercise on hippocampal volume in humans: a systematic review and meta-analysis"
Author: Joseph Firth, et al.