I completely agree and absolutely intend to discuss that in the book, thank you. When you say "brain health" do you mean actual neurological changes taking place in the brain, or underlying mental health issues like depression and anxiety?
I've been looking closely at this distinction between mind and brain for over a decade and I have to say the evidence is very thin as to nature vs. nurture wrt anxiety and depression. Moreover, ask any professed expert about the differences between chronic stress and "generalized" or otherwise anxiety, on the one hand, and sleep disturbances and depression on the other. The more certain they seem of the answer you more you know they are not honest arbiters.
The most recent work on sleep suggests a glymphatic system that washes toxins from the brain especially well during sleep. More to your question, the best work I've seen suggests that many mental health concerns can not be treated well if there's an underlying sleep disorder.
Taking a step back, if any person is under a lot of stress AND not sleeping well, and for years on end, the distinction between mind and brain and body would seem to matter little. They are suffering and in need of serious help and likely to self-medicate. However, doctors still today do not know how to treat sleep or stress concerns and specialists are all over the place, from therapists to neurologists to psychiatrists and behavioral health specialists.
Feel free to reach out to me personally. My contact info is in my profile.
Back to telomerase (Blackburn won the Nobel) and the glymphatic system (Nedergaard will win the Nobel). In short, chronic stress causes significant damage across the body and down to the cellular level. Sleep is the body's way to recover and the glymphatic system appears to be the cleaning process in the brain, down to the cellular level. When you have much more damage and insufficient recovery, something really has changed, like a car driven too fast, too hard, without oil changes for a decade.