I wouldn't call it "debunked". All these were later answered by author, I don't have sources, but I remember it was on author's blog and also on some podcasts*. I remember that he said all these will be answered also in second edition.

EDIT: 90% sure it was on one of these https://duckduckgo.com/?q=matthew+walker+site%3Apeterattiamd...

Thank you for sharing, this was an interesting read. I wonder if the rest of the book also suffers from this.

To be fair though (not that it excuses it) but pop-science/livestyle book written by academics to gain more notoriety usually suffer from this issue that a lot could be fixed by doing X. Livespan by David Sinclair also does this by basically pinning everything on aging.

It makes for a good read but I think it's best to always keep a healthy skepticism.

Slightly off topic but I always understood these types of books (scientific, biographical, medical) go through extensive fact checking before legit publishers will publish them. Is that not the case? Or did the author just serve as his own fact checker for that book?