"anyone want to venture a comment on whether the two are related?" Everything this thread will lead to is right here, in this question. It is not about a solid answer, just a whimsical discussion. Honestly, not my thing. That being said:
"I read somewhere that the "highs" and "lows" a chess player experiences during a game, combined with the anxiety, tension and stress of high-level chess, can exacerbate or bring to the surface an existing mental illness but is unlikely to be the cause. " The first post already defines the closest approximation we will reach.
Some of the opinions are vastly more interesting than the Original question. For example, Kenpos view of the introvert. Conversely, I would say there is no real division between extravert and introvert. They are accentuated roles of a confused ego. Both cases have been ruthelessly stretched to narcissism with unabashad certainty simply to fit within aptly defined boundaries. Not a single person is exclusively either. Then to mention the artificial division it creates between the ignorant of the two groups which otherwise have no backing to despise eachothers positions. These two considerations definitely point to both an extravert and an introvert as mentally deficient. While the second point is what I would call insanity, the total focus leads to broader psychology, motive, and power. All of which, I am more interested in than a correlation between a habit(or hobby) and its diverse possibilities.
Maybe think of it this way. We're all balanced between introvert and extrovert. They're just opposite ends of a spectrum. Maybe ties in with other factors or other personality traits? For instance, if we are highly confident, it's likely that we will be equally confident by ourselves for a protracted time or with participating actively in the company of others. If we have a personality imbalance we might, however, be unhappy by ourselves and calmer in the company of others, which "takes our mind off things", or we may feel subliminally threatened by being surrounded by other people.
To be honest, that's where good manners come in. If we're brought up to display good manners, then we will always do the necessary, in the company of others. That is to display basic politeness. And maybe we've all heard by now about Covid dogs and the fact that they can't stand their own company, very often, which can frighten them and makes them intensely nervous, because they were never used to being by themselves when they were puppies.
Chess might be good for people who spend lots of time with others and maybe it might not be so good for those who are already loners or who feel at odds with society. Maybe low-key sociopaths or, maybe more likely, suffering from long-term, acute depression. I've known a good few chess players who have committed suicide.
Humans are just like computers. We have processing power, we have stamina.
Just like computers, the conditions that the processor/brain is maintained correlate to the lifespan of the processor.
Play chess all day in a dark room, with minimal social interaction, absolute focus, and basic necessities. You could be so passionate about chess to begin with, but eventually you will seek an environment that satisfies your well-being. Like a better cooling system, a more nurturing fruitful environment.
Maybe chess played in moderation won't cause certain people mental problems, but excess chess to the extent that it's an exhausting obsession can cause problems.