The hippocampus, the brain region primarily responsible for memory formation, begins to shrink at approximately 1 to 2 percent per year from the late thirties. It is among the first regions affected in Alzheimer's disease. In 2011, a randomised controlled trial published in the Proceedings of the National Academy of Sciences demonstrated that a one-year aerobic exercise programme increased hippocampal volume by 2 percent in adults over 60, while the control group who performed stretching showed a 1.4 percent reduction over the same period. This was not a small finding. It represented a reversal of expected age-related hippocampal atrophy through exercise alone.
Brain-Derived Neurotrophic Factor
The primary mechanism through which aerobic exercise benefits the brain is brain-derived neurotrophic factor, BDNF. BDNF is a protein that supports the survival of existing neurons, promotes the growth of new neurons and synaptic connections, and supports the cellular processes involved in learning and memory. Aerobic exercise is the most potent non-pharmacological stimulus for BDNF production. A single bout of aerobic exercise raises circulating BDNF levels within minutes, and consistent training over months produces lasting elevations in baseline BDNF.
Cerebral Blood Flow and Vascular Dementia
Physical fitness improves cerebral blood flow and microvascular health in the brain. Vascular dementia, caused by reduced blood supply to brain tissue, is the second most common form of dementia after Alzheimer's disease, and in many cases the two co-exist. Maintaining cardiovascular fitness is one of the most direct ways to protect the small blood vessels that supply the prefrontal cortex and other high-level cognitive regions.
Sources
- Erickson, K.I., et al. (2011). Exercise training increases size of hippocampus and improves memory. Proceedings of the National Academy of Sciences, 108(7), 3017-3022.
- Cotman, C.W., & Berchtold, N.C. (2002). Exercise: a behavioral intervention to enhance brain health and plasticity. Trends in Neurosciences, 25(6), 295-301.
- Northey, J.M., et al. (2018). Exercise interventions for cognitive function in adults older than 50: a systematic review with meta-analysis. British Journal of Sports Medicine, 52(3), 154-160.