Is there a biological process that explains how high altitude impacts suicide rates, or are there social variables that aren't controlled for. This paper gets

Is there a biological process that explains how high altitude impacts suicide rates, or are there social variables that aren't controlled for. This paper gets a lot of scrutiny, but it's been out for over a decade and hasn't been debunked or explained. I've been mulling over this one for awhile, and have had several conversations with reasonably informed individuals in related fields. There's a lot of theories, many of which are explored in the comment section here. If you strongly believe in a theory, I'd like to remind you that this is a line of inquiry that could have life saving implications.