[Tenoke]

Long before that specific book came out. If you look at how they arrived at the recommendation here, a lot of it was based on discussions and voting by 15 experts chosen by the US Department of Health.

Actual studies are much less conclusive (see the one we are commenting on for example) and the evidence for 8 hours of sleep is shaky and the difference from 6 to 8 is rarely especially big even when it is supported with anything under 6 and over 8 having negative effect.

Check this systematic review (first result of my search[0]) which seems extremely sympathetic to 8 hours, yet the actual results are:

>compared with 7 h of sleep per day, a 1-h decrease in sleep duration was associated with 6% increased risk of all-cause mortality and a 1-h increase in sleep duration was associated with a 13% increased risk of all-cause mortality (N = 241 107 adults in 43 articles)

So, going from 7 to 8 hours increases risk more than going from 7 to 6!

Further

>Itani et al. (2017) reported that short sleep duration (<6 or ≤7 h/day) was not significantly associated with the incidence of depression compared with normal sleep duration (N = 16 257 adults in 2 articles)

>Lo et al. (2016) reported that extreme sleep durations (both short and long) were associated with cognitive decline compared with the reference sleep of 7 to 8 h/day (N = 97 264 adults in 18 articles)

But again it's only at the extremes that there is decline, which seems to be more like 3+ hours less than 8 a day.

>Health-related quality of life No systematic review was identified that examined the association between sleep duration and health-related quality of life.

etc. If you go through actual studies and systematic reviews it is really hard to make much of a case that 6 hours is much worse (if at all) than 8, yet alone anything more than that.

0. https://cdnsciencepub.com/doi/full/10.1139/apnm-2020-0034

[Pyramus]

This is one of my favourite topics that seems straightforward (What's the optimal sleep length?) but is a lot more tricky.

> If you go through actual studies and systematic reviews it is really hard to make much of a case that 6 hours is much worse (if at all) than 8, yet alone anything more than that.

The absence of evidence that 6 is much worse than 8 hours is not evidence that 6 is not much worse than 8 hours. It doesn't matter that much in this case because we already agree that it's worse - the question is how much worse.

Better or worse is measured in averages, on a population level, and here we see exactly the adverse health outcomes you cited (and a lot more that you didn't cite) from [1].

Here is where things get tricky for two reasons:

1) Population studies don't translate into personal health advice - there are plenty of folks striving on 4 hours a night (but they are rare in relative terms).

2) Overly long sleep durations are also associated with adverse health outcomes, and we don't know why! We believe we have a good understanding why short sleep is linked to some health outcomes linked to certain metabolic pathways, e.g. obesity or diabetes. And also we can take one individual, restrict their sleep, and see that their cognitive performance is impaired, and from here, it is reasonable to assume we understand the link between short sleep and accidents and injuries.

For the overly long sleep however, we have no idea (as far as I'm aware of).

[Tenoke]

>The absence of evidence that 6 is much worse than 8 hours is not evidence that 6 is not much worse than 8 hours.

It's not absense of evidence as in hasn't been tested - they have been compared and it doesn't really come off as worse or at best only a little worse (and in some cases better than 8).

>It doesn't matter that much in this case because we already agree that it's worse - the question is how much worse.

Who is this 'we'? My whole point is that people have this assumption and keep looking for ways to justify it even when confronted with evidence that it might not be the case as in the study posted here or the systematic review I posted.

>and here we see exactly the adverse health outcomes you cited (and a lot more that you didn't cite) from [1].

But we don't see that. What I cited was that the evidence doesn't even suggest worse outcomes at 6 vs 8 hours in the biggest analyses out there.

[Pyramus]

I don't understand. The study you cited, a meta-analysis, reviews the adverse effects of short and long sleep on

* Mortality

* Incident cardiovascular disease

* Incident type 2 diabetes

* Mental health (incident depression)

* Brain health (incident cognitive disorders)

* Cognitive function

* Falls

* Accidents and injuries

and six other outcomes. The authors conclude:

> Conclusion

> A comprehensive body of evidence supports the presence of a U-shaped association between sleep duration and health outcomes in adults. Dose–response curves showed that the sleep duration that was most favourably associated with the health outcomes that were examined was around 7–8 h per day in adults, with no apparent modification of the effect by age in the few studies that looked at it.

[Tenoke]

I specifically cited the actual results from the meta-analysis. In the conclusion and abstract they seem to mostly talk about 7-8 vs really short or longer sleep but when you look at the analysis there's barely any adverse effects at 6 (and indeed 6 is better than 8 and only a tiny bit worse than 7 on the most important thing from most studies - all-cause mortality).

Yes, of course sleeping, say, 2 hours a night is too little. My claims and quotations were about 6 hours, which is roughly what the people in OP slept, too.

[Pyramus]

It seems to me you are picking one outcome, all-cause mortality (link to the study in question with nice dose-response curves [1]) but ignoring cardiovascular disease, type 2 diabetes, brain health, cognitive function, falls, accidents and injuries, and obesity?

> My claims and quotations were about 6 hours, which is roughly what the people in OP slept, too.

It's not clear how comparable the numbers are. The study from OP [2] reports sleep as measured by actigraphy (5.5h), time in bed (8h) and self-reported sleep (7.2h). What the meta-analyses most likely have studied (I haven't checked) is self-reported sleep.

[1] https://www.ahajournals.org/doi/pdf/10.1161/JAHA.117.005947

[2] https://economics.mit.edu/files/16994

[Tenoke]

I cited 4 outcomes, starting with both the most important one and the one with most studies and subjects behind it. There wasn't an outcome where the big negative effect is there at 6.

You are proving my point - even when presented with data against the 8 hours myth you try to twist it in every way to confirm your prior belief and wouldn't even consider if the data might just be correct.

[shlep21]

The absence of evidence that 6 is much worse than 8 hours is not evidence that 6 is not much worse than 8 hours.

If sleep studies show that 6-hour sleepers do better than 8-hour sleepers on a variety of metrics... that definitely counts as evidence.

It doesn't matter that much in this case because we already agree that it's worse

The parent comment literally cites a study that suggests 8 is worse than 6.