We know that exercise is a powerful treatement for Alzheimer's disease. But how?

In Beating the Dementia Monster, I tell the story of my dramatic walk-back from the cliff-edge of dementia.  My first step in reversing the effects of the disease was to get off the couch and get to the gym.  I did this when my care team and scientific material I read said that lifestyle changes are necessary for someone confronting the disease.  And initiating physical exercise was the most powerful of these changes.

But why is exercise so powerful?  We discussed the hypothesis that's most popular among neuroscientists, and that is that the brain generates the protein "brain-derived neurotrophic factor" (BDNF) during exercise.  That certainly happens, and BDNF has the power to repair damaged brain cells as well as to prompt stem cells in the hippocampus to form new neurons.  

So that's an explanation.  But is that the whole story?  Maybe not.

According to new research published in the journal Neuron, there is a hormone generated during exercise with similar power.  It's called irisin.  The research was conducted at Massachusetts General Hospital.

So what's the deal with irisin?  According to the researchers, they found that "irisin significantly reduces beta amyloid levels by elevating the levels of soluble NEP secreted from astrocytes."  So NEP attacks beta amyloid plaques.  What's NEP?  NEP is an enzyme secreted by special brain cells called astrocytes.  We briefly discussed astrocytes about three years ago, noting that their failure contributes to the advance of Alzheimer's disease.  Apparently that's because they play a role in controlling beta amyloid by secreting NEP.  Note that the latest monoclonal antibody treatments, Aduhelm and Leqembi, work by attacking and removing beta amyloid in the brain -- just like NEP.

Here's a simpler, more easily understood narrative on this research.

So what's our takeaway from an increasingly complex picture?  Physical exercise fights Alzheimer's disease in at least two different ways.  First, it generates BDNF that heals and generates new brain cells.  But we now learn that it also encourages generation of irisin.  Irisin fights the amyloid plaques that interfere with the flow of information between cells and also kill cells outright.

Moral of the story?  Get to the gym!