> that at even 6 hours you have less all-cause mortality than at 8 hours of sleep[0]
Well, yeah; if you're sleeping more than 7 hours of sleep per night, it's likely because you're unhealthy somehow, such that your CNS takes longer than normal to clear out a sufficient amount of gunk for you to feel rested.
The real stat is "if you sleep less than you need to feel rested, you're at heightened risk of neurodegenerative diseases"; it's just hard to turn that into quantitative statistics.
>you sleep less than you need to feel rested, you're at heightened risk of neurodegenerative diseases
Do you have anything corroborating that? Eating less than you need to not feel hungry doesn't seem to be damaging (up to a point) so a priori I don't see a reason to believe sleeping somewhat less than you subjectively want to has big negative outcomes without evidence.
Why do you believe that those two processes are in any way analogous?
Hunger is an explicit suite of hormonal control-system signals (leptin + ghrelin) evolved as an "instinct" to direct food motivation toward medium-term calorie caching in a seasonal feast-or-famine environment. You get "more hungry than you need" because your body is actively/intentionally trying to acquire "extra" calories to use to build fat stores.
Tiredness isn't an intentional conscious signal; it's rather the experiential qualia of a direct physiological problem — the gradual degradation of the brain's ability to function. Well-restedness is just the feeling of not being tired — of not having the inflammatory processes, brain fog, confusion, etc. that stem from said brain-function degradation. Sleep clearly rewinds this degradative process; getting little sleep results in impaired recovery. People (when not being woken up by an alarm) tend to sleep until the degradation is fully fixed, however long that takes. People who have harmed their brain in other ways — e.g. with alcohol, with hypoxia, with a concussion, etc. — take longer to naturally awaken from sleep, because their brain is recovering from a deeper state of degradation.
I'm not claiming anything here about the mechanism by which sleep enables recovery from the gradual brain-function degradation caused by being awake for a long time; but it's pretty clear that sleep does have that effect.
Well, yeah; if you're sleeping more than 7 hours of sleep per night, it's likely because you're unhealthy somehow, such that your CNS takes longer than normal to clear out a sufficient amount of gunk for you to feel rested.
The real stat is "if you sleep less than you need to feel rested, you're at heightened risk of neurodegenerative diseases"; it's just hard to turn that into quantitative statistics.