More than 80 percent of North Americans over the age of 85 suffer from some form of dementia. A new study in rats helps to explain why exercise could help to prevent or delay this dreaded condition (Sci Rep, 2017 Sep 7;7(1):10903). A group of rats were kept in cages that had exercise wheels, while the control group had no exercise equipment. One month with exercise wheels caused their brains to triple the rate that they made new nerves in the part of the brain called the hippocampus, where memory of past experiences is stored. A month in the life of a rat equals about four years in a human.
• The new nerves were larger and had longer dendrites that are used to send messages to other hippocampal nerves. The new nerves were the stimulatory nerves that increase memory.
• They also had a decrease in the hippocampal inhibitory nerves that interfere with memory.
Which Types of Exercise are Best for the Brain?
Another study with rats was designed to simulate three types of exercise used by humans, to compare the increase in new nerves in their memory-governing hippocampi with:
• long distance running
• high-intensity interval training (repeated short bursts of all-out effort separated by periods of rest)
• weight lifting
The rats that ran long distances on exercise wheels at their own choice of speeds had the greatest increase in nerves associated with memory, and the more miles they ran, the more their brains produced brain-derived neurotrophic factor (BDNF) that causes new brain nerves to grow (J Physiol, 2016 Apr 1; 594(7): 1855–1873).
The rats that did high-intensity interval training (HIIT) were put on little treadmills that required them to sprint very fast for three minutes, followed by two minutes of slow jogging, and repeated this twice, for a total of 15 minutes of running. The HIIT group had much less new brain nerve growth and lower levels of BDNF, probably because they spent little time exercising because they had no running wheels in their cages.
The weight-lifting group climbed a wall with tiny weights attached to their tails. This group had more new nerve cells than the HIIT sprinters, but still had far less brain growth than the long distance runners. Overall, this study showed that in rats, the total time spent exercising was the most important factor in promoting new brain-cell growth — more significant than intensity or effort against resistance. Another study in mice showed that endurance exercise raises brain levels of irisin that helps to govern memory by increasing BDNF and activates genes involved in memory (Cell Metabolism, October 10, 2013).
These animal studies require biopsies of the rats' brains after exercise, which cannot be done in humans, so we have no way to know if the same results would be found in humans. However, we do have many studies that confirm the benefits of exercise on human memory, and the animal studies help us to understand the probable mechanisms.
Studies in Humans
A study of 60 men and women, ages 65 to 85, had them ride an exercise bike for 20 minutes three times a week for 12 weeks. Those who exercised had no rise in brain levels of choline, while those who did not exercise had elevated levels (Translational Psychiatry, 2017; 7 (7): e1172). Choline levels rise with nerve cell damage such as is found in Alzheimer's disease.
An outstanding review of hundreds of articles in the world's scientific literature showed that exercising older people have far less loss of brain function with aging, less brain blood vessel damage, larger hippocampal brain size for better memory, less loss of brain tissue with aging, better spatial memory, better communication between brain nerves and improved ability to learn new facts (Mayo Clin Proc, 2011 Sep; 86(9): 876–884). Exercise appears to be one of the most effective treatments for brain- debilitating Parkinson's disease (Neurology, 2011 Jul 19;77(3):288-94.) A regular exercise program is among the best methods we have at this time to help stave off dementia associated with aging.