For decades, the scientific consensus has been that exercise improves both mental and physical health. Numerous studies over the years have demonstrated that this is the case, but some have also found that exercise plays a role in preventing Alzheimer's disease.
A new joint study from Columbia University, the Federal University of Rio de Janeiro in Brazil, and Queen's University in Canada answers a key question: Why does exercise protect against Alzheimer's? Apparently, a recently discovered hormone called irisin is to blame.
Published in the peer-reviewed journal Nature Medicine, "Exercise-linked FNDC5/irisin rescues synaptic plasticity and memory defects in Alzheimer's models" explores what effect irisin has on the brain.
Previous studies have suggested, the researchers note, that irisin is released during physical activity and that it plays an important role in energy metabolism. Research has also found that irisin promotes neuronal growth in the hippocampus, a region of the brain that is often associated with memory.
"This raised the possibility that irisin may help explain why physical activity improves memory and seems to play a protective role in brain disorders such as Alzheimer's disease," lead author Ottavio Arancio explained in a press release.
The researchers examined tissue samples from brain banks, established the presence of irisin in the hippocampus, and found that individuals suffering from Alzheimer's disease had reduced levels of this important hormone. In order to further explore how irisin affects the brain, the researchers conducted a number of experiments on healthy mice.
The mice were given infusions of beta-amyloid, "a sticky compound that accumulates in the brain, disrupting communication between brain cells and eventually killing them," per the Alzheimer's Association.
Of the mice that were studied, only the ones who swam regularly for five weeks did not develop memory impairment caused by beta-amyloid, suggesting that regular physical activity boosts irisin levels, and therefore improves memory and protects against Alzheimer's disease.
In order to test this, the researchers blocked irisin with a drug. This eliminated the benefits of swimming. Mice who were treated with irisin-blockers performed on par with sedentary mice, but not better. These findings also suggests that irisin plays a key role in memory improvement.
According to the scientists, this study shows that irisin could be exploited to develop new drugs for combating and preventing dementia. Not everyone is able to exercise regularly, so developing such drugs could prevent cognitive decline in the elderly.
"For those individuals, there's a particular need for drugs that can mimic the effects of irisin and protect synapses and prevent cognitive decline," lead author Ottavio Arancio said.
"In the meantime, I would certainly encourage everyone to exercise to promote brain function and overall health," Arancio concluded.