Yeah I feel like the results could be stated more clearly. At any rate this doesn't seem to associate risk with any chosen behavior.

It seems to me that perhaps the data better supports that dementia is correlated with unintentional and short naps. This makes it sound like they think it is causal, which I doubt.

Easily. I'm 80% sure that they did reverse cause and effect.

Yes, ironically they even admit possible reverse causal effect along with many other causal variables. Frankly, this is not exactly stellar research in my view, at least with the rather reckless insinuations not supported.

> I wonder if this study is missing some quite big issues here.

Definitely seems like a possible "correlation is not causation".

I would find it hard to believe that sleep is somehow biologically harmful.

So, like your example, excessive or unintentionally napping is instead a sign of an underlying issue or poor health. Possibly the body trying to sleep to repair some damage?

I wonder what unitentional napping means as well. I assume it's for example watching TV/reading a book on the sofa and falling asleep as opposed to wanting to fall asleep with a book or while watching TV.

I think we need to understand what intentional vs unintentional napping is.

See what I mean?

Except intentional napping, which could be "yawn, I slept bad last night; I'm gonna go take a nap" is not a risk.