[totony]

IIRC there are negative effects of oversleeping; some mininal health issues, but cognition is the same as a 8-9hour sleep

I read a few studies when i started bodybuilding and that seemed to be the consensus

Also undersleep affects cognition to a signifiant degree, iirc it was 40% diminution day one, 60% day 2 on memory tasks (and you have the same health issues as oversleep, perhaps to a higher degree)

[mindB]

I did a brief search because I was curious who was remembering correctly here. There have been several studies correlating "long" sleeping with mortality, but the study I found that attempted to control for confounding variables[1] seems to suggest that most of the differences in mortality in the populations studied can be explained by "depression and low socioeconomic status". It seems like a lot more study has been devoted to undersleeping than oversleeping, and I can't find anything convincing as far as maximum healthy sleep time and effects of over-sleeping. One study I still want to look at but haven't gotten around to yet is the stuff the NSF produced in 2015 when making its recommendations about sleep duration.

[1] https://academic.oup.com/sleep/article/29/7/881/2708387

[tryonqc]

It appears there is indeed a link between short/long sleep and mortality. As you said, the possible causes are usually not reviewed. This concerns me as I do sleep 9h+ on average. (But then again I do have an eye-illness that require a lot of concentration to overcome)

> Conclusion: Both short and long duration of sleep are significant predictors of death in prospective population studies. > (...) > Future studies should be designed to answer the question whether sleep duration is a cause or simply a marker of ill-health. https://academic.oup.com/sleep/article/33/5/585/2454478?sear...

> Long sleep was significantly associated with mortality, incident diabetes mellitus, cardiovascular disease, stroke, coronary heart disease, and obesity. https://linkinghub.elsevier.com/retrieve/pii/S1087-0792(17)3...