Once and for All: Aerobic Exercise Helps Maintain Brain Volume

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For over a decade, researchers have suspected that aerobic exercise boosts cognitive function and maintains brain health via neurogenesis (the birth of new neurons). Neurogenesis is believed to bulk up gray matter volume, prevent neural atrophy, and increase the size of certain brain regions.

Some neuroscientists even refer to aerobic exercise as “Miracle-Gro for the brain." But there are also some naysayers who have fueled a constructive "correlation does not imply causation" debate about whether or not aerobic exercise actually causes the hippocampus (a memory hub) to increase in size.

Finally, a new meta-analysis confirms that aerobic exercise does, in fact, affect hippocampal volume in the human brain. The findings of this report, "Effect of Aerobic Exercise on Hippocampal Volume in Humans: A Systematic Review and Meta-Analysis," were published online ahead of print in the journal NeuroImage.

For this meta-analysis, an international team of researchers systematically reviewed 14 clinical trials, which involved brain scans of 737 people before and after aerobic exercise programs or under control conditions. More specifically, the team examined effects of aerobic exercise, which included stationary bicycling, walking, and treadmill running. The length of the aerobic interventions ranged from three to 24 months with a spectrum of two to five moderate-to-vigorous physical activity (MVPA) sessions per week.

Typically, brain health decreases as we get older. The average brain shrinkage experienced by men and women is approximately 5 percent per decade after age 40. The good news is that aerobic exercise appears to increase the retention of left hippocampal volume and may improve memory function along with helping to maintain overall brain health as we age.

What Makes Aerobic Exercise Like Miracle-Gro for the Human Brain?

Brain-derived neurotrophic growth factor (BDNF) is a protein increased by aerobic exercise that acts like neuron fertilizer. BDNF promotes both neurogenesis and functional connectivity between brain regions.

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Studies on rats and mice have consistently shown that physical exercise increases the size of the hippocampus. However, until recently the empirical evidence of aerobic activity affecting hippocampal volume in humans has been inconsistent. That said, the current meta-analysis reaffirms a significant effect of aerobic exercise on left hippocampal volumes in the human brain. In a statement, lead author and NICM postdoctoral research fellow Joseph Firth said, “this study provides some of the most definitive evidence to date on the benefits of exercise for brain health.”

Firth concludes that along with improving regular, healthy brain aging, the results of this new systematic review and meta-analysis have implications for the prevention of aging-related neurodegenerative disorders such as Alzheimer's disease. Notably, aerobic exercise is one of the very few proven methods for maintaining gray matter (GM) volume and white matter (WM) functional connectivity into older age.

If you need one more reason to stay physically active on a regular basis, hopefully, the growing mountain of empirical evidence showing that aerobic exercise affects brain size will inspire you to move more.