1) Correlation is not causation. It could be that the dope mean just coincides with the reduce levels of Hydrogen peroxide.
MAO-B degrade dopamine it is clearly causative.
But you’re saying is the dopamine, I’m saying is the hydrogen peroxide that is not produced when the dopamine is not metabolize. Dopamine has no real function in the body other than neurological. But oxidative stress is critically important especially to lifespan.
A little late to this conversation, but I want to point out that it appears dopamine does have functions other than neurological.[1] Of course one might take the view that immune function is regulated by the nervous system and thus it may not be a direct pathway.