Alexey Guzey’s Theses on Sleep gained a lot of popularity and acclaim on LessWrong and among people I follow on social media, despite largely consisting of what I think were weak arguments and misleading claims. I found that a bit surprising, so I decided to write a post pointing out several of the mistakes I think he’s made, and reporting some of what the academic literature on sleep seems to show. 

Sleep deprivation is associated with *both* depression *and* mania

One of Guzey’s theses is that “depression triggers/amplifies oversleeping while oversleeping triggers/amplifies depression.” The first piece of evidence he uses to support that is people on /r/BipolarReddit saying that they sleep a lot when depressed, and sleep very little when manic. However, there’s a big problem with using that as evidence. 

Guzey’s /r/BipolarReddit evidence is misleading

The DSM-5 specifies subtypes of depression that have opposing relationships with sleep. Depression with melancholic features is associated with early morning awakening, whereas depression with atypical features is associated with hypersomnia.

Guzey’s evidence is misleading because people with bipolar disorder are disproportionally prone to having atypical features during their depressive episodes. So, unsurprisingly, his evidence from bipolar disorder patients is not representative of what you see in the general population: both long and short sleep duration are associated with depression (and, relevantly, suicide as well, in adults as well as adolescents). 

I’m surprised no one in the comments of this post brought up this objection – it only takes a very quick Google Scholar search to see that the relationship between sleep duration and depression is not linear. 

Chronic sleep deprivation might be associated with *decreased* BDNF expression, as shown by Guzey’s own sources

Guzey hypothesizes that 

Sleep deprivation appears to increase BDNF [and therefore neurogenesis?]

He then proceeds to link to a few papers that showed up when he Googled “sleep deprivation bdnf”. These sources agree that acute sleep deprivation increases BDNF expression, but some also say that the opposite may happen when sleep deprivation is chronic, which Guzey fails to mention in his post.

From The Brain-Derived Neurotrophic Factor: Missing Link Between Sleep Deprivation, Insomnia, and Depression:

Chronic sleep deprivation and insomnia can act as an external stressors and result in depression, characterized by hippocampal BDNF downregulation along with disrupted frontal cortical BDNF expression, as well as reduced levels and impaired diurnal alterations in serum BDNF expression.

Guzey also links to The link between sleep, stress and BDNF, which seems to be only an abstract. After a bit of searching, I found this full-text paper with some of the same authors, which appears to have an almost identical abstract (?). It concludes with the following:

[O]ur findings are in line with the hypothesis of an increased stress vulnerability due to sleep loss which may lead to a decrease in BDNF. [...] While we report a reduction of BDNF levels linked to sleep disturbance reflecting chronic stress on the one side, we and others consistently showed that prolonged wakefulness caused by SD (partial or total), which can be considered as an acute stressor for the brain, leads to a rapid increase of BDNF (1,36).

Our priors about sleep research should be high

I feel grumpy, dumb and distractable every time I sleep less than 7 or so hours. I can’t do things that require focused attention like solving physics homework problems very effectively, and I don’t get nearly as much pleasure when I attempt doing so. My memory becomes very poor: after a recent night of <6 hours of sleep, I somehow forgot the reasoning behind several Manifold Markets trades I had made the prior evening and just stared at them in utter confusion for several minutes before remembering. 

I have the impression that most people have a similar experience. Guzey has a cute explanation of how this is consistent with his thesis that sleep deprivation doesn’t make you grumpy or dumb, but the fact that I and others I know have this experience with sleep deprivation obviously makes it so that I have a high prior that it’s harmful to cognition and mood. It sounds a lot more plausible that sleep deprivation being harmful in those ways is causing both my personal experience with it to be terrible and academic research to find that it’s harmful, instead of a different factor explaining each thing. Guzey has to add quite a few epicycles to his theory to explain the evidence. 

To the extent that you and the people you know feel the same way I do after a night of sleep deprivation, your prior should be high as well. 

Most of Guzey’s arguments against trusting sleep research are bad

Guzey claims that “most sleep research is extremely unreliable and we shouldn’t conclude much on the basis of it,” but there are problems with that. Firstly because he doesn’t seem to believe that about sleep research that favors his hypotheses. Guzey, after all, uses sleep research to show that Matthew Walker’s book is terrible and fraudulent. So it seems that he wants to trust sleep research when it says that sleep deprivation is not as bad as Walker shows, but doesn’t want to trust it when it says that sleep deprivation is not harmless.  

Secondly, he bases that assertion on a claim that sleep science is “mostly just rebranded cognitive psychology” (and that it is only not facing a severe replication crisis because sleep experiments are expensive), which is very misleading. Unlike the famously unreliable cognitive science results, the finding that sleep deprivation is harmful for cognition (1) in fact gets replicated a lot (see the section below on meta-analyses of sleep restriction studies, as well as this meta-analysis of total sleep deprivation studies) and (2) is consistent with a lot of people’s experiences (for examples, see this addendum.) So it’s hard to see how Guzey’s criticisms apply. 

Moderate sleep restriction impairs cognition

Guzey says, in his post: 

I wrote large chunks of this essay having slept less than 1.5 hours over a period of 38 hours. I came up with and developed the biggest arguments of it when I slept an average of 5 hours 39 minutes per day over the preceding 14 days. At this point, I’m pretty sure that the entire “not sleeping ‘enough’ makes you stupid” is a 100% psyop. It makes you somewhat more sleepy, yes. More stupid, no. I literally did an experiment in which I tried to find changes in my cognitive ability after sleeping 4 hours a day for 12-14 days, I couldn’t find any. My friends who I was talking to a lot during the experiment simply didn’t notice anything.

I don’t think that “feeling smart after sleep deprivation” (or any of those other things) is nearly enough evidence to make you conclude that “ ‘not sleeping ‘enough’ makes you stupid’ is a 100% psyop” if you start out with even a halfway reasonable prior, and especially if you appropriately update on what the sleep literature says. 

I looked for meta-analyses that investigated the effect of experimental or quasi-experimental nighttime sleep restriction on cognition. I found three, and am quoting the relevant conclusions from them:

The neurocognitive consequences of sleep restriction: A meta-analytic review:^[1] 

The current meta-analytic review revealed that restricted sleep results in significant neurocognitive deficits (g = −0.383) in a sample of 1688 participants derived from 71 different study populations. This effect was apparent across multiple cognitive domains, with the largest effects being observed on measures of sustained attention (g = −0.409) and EF (g = −0.324), and within these domains, attentional lapses and (g = −0.516) and behavioural inhibition (g = −0.464) specifically.

[...]

Meta-regression analyses indicated that age-adjusted sleep deficit (β=-.206, p=.033), cumulative days of restricted sleep (days; β=-.015, p=.019),^[2] subjective sleepiness (β=-.040, p=.016), biological sex (β=.0318, p=.009), and sleep latency (β=.012, p=.013) accounted for a significant proportion of the variance in the observed effect of sleep restriction on overall cognitive abilities.

Sleep Loss and Performance in Residents and Nonphysicians: A Meta-Analytic Examination:

Chronic partial sleep loss also resulted in a significant reduction in cognitive performance, with a correct d value of -.886. 

A Meta-Analysis of the Effect of Experimental Sleep Restriction on Youth’s Attention and Hyperactivity (on people under 18 years old only):

A total of 13 samples (N = 268) examined the difference in youth’s attention performance between baseline (control) sleep and restricted sleep. The overall effect size of −0.19 was significant (95% CI: −0.34−0.03; p = .02); Q(13) = 21.98, p = .04, I 2 = 45.40% (see Figure 2). The I^2 index of 45.40% indicates a small to moderate amount of heterogeneity in effect sizes across studies (Card, 2012). However, the trim and fill method for addressing publication bias (Duval & Tweedie, 2000a; Duval & Tweedie, 2000b) revealed asymmetry in the funnel plots for the difference in attention outcomes between sleep restricted and baseline sleep. One study to the left of the mean was unmatched. The counterpart of this study was imputed to the right of the mean, resulting in a non-significant and small adjusted effect size of −0.14 (95% CI: −0.32–.04).

Six samples (N = 279) examined the difference in attention between extended sleep (sleep extension) and sleep restriction. The overall effect size of −0.37 was significant (95% CI: −0.55 to −0.19, p < .0001) and represents a small to medium effect size (Lipsey & Wilson, 2001), though this effect was heterogeneous between studies Q(5) = 15.29, p = .009, I 2 = 67.30% (see Figure 2). The I 2 index of 67.30% indicates a moderate to large amount of heterogeneity in effect sizes across studies (Card, 2012). Based on trim-and-fill analyses, asymmetry was also present for attention outcomes between restricted and extended sleep, with two studies to the left of the mean unmatched, resulting in a significant adjusted effect size of −0.26 (95% CI: −0.46 to −0.05), which is considered a small to medium effect (Lipsey & Wilson, 2001).

The average age-adjusted sleep deficit in the first meta-analysis was 3.83 hours (SD = 1.25). (This is in comparison with the median recommended amount of sleep for each age group (so 8 hours per night for non-elderly adults), not the average amount of sleep people in each age group actually get.) I couldn’t find information about the other ones, but I have a high credence that they examined studies with a roughly similar protocol; I’ve combed through a lot of individual sleep restriction studies before and they rarely seem to involve making people sleep for < 3.5 hours. 

I also found a meta-analysis investigating the effects of napping, and it finds that it’s beneficial, which is probably relevant:

Effects of a Short Daytime Nap on the Cognitive Performance: A Systematic Review and Meta-Analysis:

Overall cognitive performance did not differ at baseline (t0) between groups (effect size −0.03, 95% CI −0.14 to 0.07), and improved in the nap group following the nap (t1) (0.18, 0.09 to 0.27), especially for alertness (0.29, 0.10 to 0.48). Sensitivity analyses gave similar results comparing only randomized controlled trials, and after exclusion of outliers.

There’s also (weaker) evidence that, contrary to what Guzey hypothesizes, there is no cognitive adaptation to chronic sleep restriction. From this article:

Contrary to a popular belief that healthy adults can acclimate to sleep loss, the effects of chronic partial sleep loss appear to be cumulative.^9-11 Specifically, sleepiness has been found to increase⁹ and performance on tests of vigilance and mathematical calculations to decline across 7 days of 5 and even 7 hours of sleep per night.^10,11 Subjects often underestimate their own degree of sleep-related impairments in vigilance after 1 week of partial sleep restriction.^9,12 Thus, they may mistakenly believe that they have acclimated to sleep deprivation.

In addition to reduced vigilance, verbal processing and complex problem solving^13,15 are impaired with both short-term and chronic partial sleep loss.

See also footnote 2 (^[2]) on the matter of cognitive adaptation. 

I do recognize that even meta-analyses of experimental studies can obviously be very problematic, and so this section is not conclusive evidence that moderate sleep restriction impairs cognition (and not only because conclusive evidence is not a thing). But it’s not as if Guzey has any better evidence to argue that “ ‘not sleeping ‘enough’ makes you stupid’ is a 100% psyop.”

Occasionally stubbing your toe is good for health and promotes more efficient toe healing

One of Guzey’s theses is that “[o]ccasional acute sleep deprivation is good for health and promotes more efficient sleep.” His argument supporting that thesis is pretty much that, because some types of acute stress (such as exercising and fasting) are good, and acute sleep deprivation causes acute stress, then acute sleep deprivation is also good. (Yes, that does seem to actually be the entirety of his argument in that section. You can read it yourself.)

The obvious problem with that argument is that the set of things that cause acute bodily stress is much larger than the set of things that cause long-term benefits. Stubbing your toe, for example, causes acute bodily stress. Guzey’s argument works equally well for showing that occasional toe-stubbing is good for health as for showing that occasional acute sleep deprivation is.

Short-term != long-term

In this section, Guzey lists lines of evidence that bring him to the conclusion that “decreasing sleep by 1-2 hours a night in the long-term has no negative health effects.” The lines of evidence are:

1. A sleep researcher who trains sailors to sleep efficiently in order to maximize their race performance believes that 4.5-5.5 hours of sleep is fine.
2. 70% of 84 hunter-gatherers studied in 2013 slept less than 7 hours per day, with 46% sleeping less than 6 hours.
3. A single-point mutation can decrease the amount of required sleep by 2 hours, with no negative side-effects.
4. A brain surgery can decrease the amount of sleep required by 3 hours, with no negative-side effects.
5. Sleep is not required for memory consolidation.

Apart from (2), we don’t have any indication of the long-term outcomes of the groups of people he mentioned. So I don’t know how these points could be more than weak and circumstantial evidence of this section’s thesis.

(For that matter, barely any of those even rigorously measure the health effects of short sleep at all. In a sense, they confirm that these people are not immediately dying or getting very acutely sick or something, and I guess I can interpret Guzey as merely wanting to claim that, but it’s not exactly a novel or surprising claim.)

(Also, the 5th line of evidence doesn’t even seem to be related to health.)

Experimental sleep restriction seems to cause short-term detriments to metabolic health

I searched Embase for meta-analyses on the effect of experimental sleep restriction on a host of health-related variables, and this is what I found.

Effects of sleep manipulation on markers of insulin sensitivity: A systematic review and meta-analysis of randomized controlled trials:

Whole-body insulin sensitivity was also reduced after short sleep when measured by the hyperinsulinemic euglycemic clamp, but peripheral insulin sensitivity was not affected. In addition, circadian misalignment and slow wave sleep suppression negatively affected insulin sensitivity, while rapid eye movement sleep disturbance and sleep fragmentation had no effect.

Effects of sleep restriction on metabolism-related parameters in healthy adults: A comprehensive review and meta-analysis of randomized controlled trials:^[3]

Participants consumed 252.8 more kcal/d (p = 0.011) under sleep restriction than under normal sleep. Partial sleep restriction resulted in a 0.34 kg weight gain (p = 0.003). Sleep restriction also decreased insulin sensitivity (standardized mean difference = −0.70, p < 0.01). Significant changes in brain activity in response to food stimuli were observed under sleep restriction, particularly regions related to cognitive control and reward.

Sleep Restriction Effects on BP: Systematic Review & Meta-analysis of RCTs:

Overall, sleep restriction did not result in significant changes in systolic blood pressure (SBP) or diastolic blood pressure (DBP) and heart rate (HR). The respective weighted mean difference (MD) was 1.0 mmHg (95%CI, -2.3-4.2; p = 0.57), -0.4 mmHg (95%CI, -3.2-2.4; p = 0.80), and 2.0 bpm (95%CI, -2.2-6.2; p = 0.34).

Sleep Disturbance, Sleep Duration, and Inflammation: A Systematic Review and Meta-Analysis of Cohort Studies and Experimental Sleep Deprivation:

Experimental sleep deprivation, either for partial or total night, was not associated with CRP [...], IL-6 [...], or TNFα [...]. Likewise, sleep restriction over several days was not associated with CRP [...], IL-6 [...], or TNFα [...].

(Eyeballing each of those meta-analyses’ lists of studies, it seems that, in most of them, time in bed was restricted to 4-5 hours, with the range being from ~3.5 to ~5.5.)

So experimental sleep restriction (presumably during short periods of time) seems to impair things like insulin sensitivity and the regulation of satiety, but not blood pressure or inflammatory markers. 

Importantly, the metabolic effects of sleep restriction found in the first two meta-analyses seem consistent with the finding that short sleep duration is associated with weight gain in observational studies (particularly in younger persons), which perhaps indicates that the adverse metabolic effects of sleep restriction don’t wane with time. 

These changes seem pretty bad. It’s unclear to what extent they translate to long-term health effects (see the section below) but those are things you perhaps should not ignore when investigating whether sleep deprivation is bad for your health. 

The evidence for a U-shaped association between sleep and mortality is actually pretty weak 

Guzey doesn’t talk about the supposedly U-shaped association between sleep and mortality on Theses on Sleep itself, but he has brought it up in a couple of other places (in the conclusion of his takedown of Walker’s Why We Sleep, and on a comment in the EA Forum) so I thought I’d tackle it here. 

For those who don’t know, a lot of epidemiological studies seem to show that the association between sleep duration and mortality is something like this:

(This specific chart comes from Shen 2016). 

But Kurina et al.’s “Sleep duration and all-cause mortality: a critical review of measurement and associations” finds that this U-shaped association is suspiciously restricted to a very specific type of study (emphasis mine): 

One interesting pattern among studies using survey sleep measures is that all of the studies reporting U-shaped associations measured sleep duration with questions about typical nighttime sleep or 24-hour sleep (Table 2). None of the studies that asked about usual bedtimes and waking times reported a U-shaped association; rather, they reported either no association [12,22,23] or only a long sleep association [6,9,34,99], or, in the case of two studies of young to middle-aged Japanese men, only a short sleep association [12,22]. That the U-shaped associations are exclusively found in studies asking about usual sleep duration may be informative and suggests the possibility of systematic response biases, with people in generally good health more likely to give a “normative” response (i.e., 7 or 8 hours) and those in worse health more likely to give a “non-normative” (shorter or longer duration) response.

It seems that you can’t take people’s reports of how many hours they sleep at face value. Further evidence of that is that studies have shown that people seem to give the same answers when asked how many hours they sleep and how many hours they spend in bed. Also, a substantial fraction of older adults (47% in this study) report sleeping >=8 hours a night, but when their sleep is actually measured, very few of them do, as pointed out in Kurina et al.’s paper. 

Kurina et al. look into studies that actually measure people’s total sleep time, and report the following:

A study employing actigraphy among women 50 to 81 years of age (n = 444) concluded that the relationship between sleep duration and mortality was U-shaped [... but] death rates by more detailed sleep categories do not show a dose response for either side of the duration distribution. The top and bottom categories (<4.5 or >7.5 hours) have relatively low mortality, albeit with small numbers, and the highest mortality risk was observed in women sleeping either 4.5—5 hours or—interestingly—between 7 and 7.5 hours.

Neither of the two studies employing polysomnography reported significant associations between sleep duration and mortality [27,36]. In both studies, sleep duration was dichotomized at fewer than 6 and 6 or more hours, precluding the possibility of finding a U-shaped effect. 

This isn’t exactly strong evidence that sleeping too much or too little is not harmful. This review only mentions three studies examining the effect of measured sleep on mortality, and two of those didn’t record sleep duration in a way that would make them able to find a U-shaped relationship. Moreover, all of these naturalistic studies probably have substantial range restriction — they mostly involve elderly or middle-aged subjects, many of whom can probably sleep as much as they want, and it’s fairly plausible that very few of those people manage to consistently sleep so much or so little that it’s harmful. Also, they measured sleep for one night only, and the study equipment might have disrupted the sleep of subjects. 

However, this review does provide evidence against six hours of sleep being associated with the lowest mortality, as Guzey has hypothesized before (as well as evidence against eight hours of sleep being associated with the lowest mortality, of course). And thus, most importantly, it also provides evidence against moderately short or moderately long sleep being harmful.

Conclusion

So here are my credences on a few relevant object-level claims:

• Shorter-than-average sleep is associated with both depression and mania: 95%
• Modulo weird edge cases like abolishing REM sleep exclusively, a single night with 4.5 to 6 hours of sleep has a negative impact on cognition the following day: 96%
  • Conditional on this, cognition does not return to baseline levels after several months of sleep restriction: 83%
• Also modulo weird edge cases, consistently sleeping between 4.5 and 6 hours per night as a non-elderly adult has some long-term negative health effects: 75%
• It’s not worth it to stress out about how much you’re sleeping, as long as you feel comfortable and productive (and you’re not (getting) manic)^[4]: 63%

I’d be happy to bet on reasonable operationalizations of those statements at those odds (unless I change my mind, in which case I’ll probably edit the credences listed here).

Addenda

Mania is really, really bad, and can be triggered by sleep restriction

 I thought I’d bring this up, since it affects how harmful we should expect sleep deprivation to be in expectation. Two years after being hospitalized for a manic episode, less than half of people regain their premorbid occupational and residential status, and the hospitalization rate of mania is pretty high, so manic episodes seem to screw people over really badly for a long time. 

And sleep deprivation might risk triggering mania if you have bipolar or a high risk of getting it. A night of total sleep deprivation seems to be able to trigger full-blown mania in a substantial percentage of people with bipolar disorder (even those currently depressed) and even cause mania-like behavior in healthy subjects. Moreover, a shift towards mania or hypomania after a short night of sleep seems common in bipolar patients. 

Given how bad mania is, it might be a good idea to try to decrease even a relatively small chance of getting it, so those at a high risk of getting bipolar disorder should probably consider these effects before experimenting with sleep restriction.

Amusing r/NewParents anecdotes about sleep deprivation

I collected a few amusing anecdotes about sleep deprivation from r/NewParents. 

From this thread, titled “Tell me you’re sleep deprived without telling me you’re sleep deprived..”:

I just unzipped my 1 month old’s sleeper to expose his nipple so I could feed him…… 🤨

My husband attempted to hand me a cat to nurse.

"There was 120ml in the bottle, there is now 50ml in the bottle, so she's drank...

Okay, this isn't that hard, there was 120 in the bottle, there is now 50 in the bottle so she's had...

Right the bottle has 50ml, she's drank 120 so there should be.. no, she's drank 50 there's 120 left so, NO!

there was 120 in the bottle, there is now 50 and it goes 50, 60, 70, 80, 90, 100, 110, 120 so she's had 120.

NO! "

i genuinely gave up and used a calculator

From “Finish the sentence: I was so sleep deprived I....”:

Filled the dryer full of wet clothes and tried to turn it on via the microwave sat above it

...ran into a laundry basket and said "excuse me" to it.
 

Turned on the Keurig to make my coffee and walked away without noticing that I forgot to put my mug under it. The worst part is I've done this 3 or 4 times now.

Forgot to put a new diaper on after taking dirty one off. Baby went commando for a while.

From “Funniest thing you’ve said while sleep deprived in the dead of night”:

Nothing will ever top my husband waking me up saying "please take the baby I can't stay awake any longer" and gently passing me a very pissed off cat that had been asleep on his lap. Note, cat weighed twice what our newborn weighed. When I told him that was a cat he looked terrified and went "but then where's the baby?!"

My husband and I woke up to our 5-month old crying and he said, “Is that ours??” Yes, my good sir, that is in fact our baby.

It was my turn to wake up for a feed and my wife woke up first so said “babe, wake up she’s crying” and I responded “what? who the hell would be crying in our house?” It was 2 weeks after our daughter got home and she’s our first 🙃 

Errata

(Let me know if you think something should be added here that hasn't been.)

• I used to have an additional quote in the section about BDNF, saying that insomniacs had lower levels of BDNF than sleep-healthy controls in a study. Guzey noted that insomniacs often underestimate how much they sleep; which prompted me to look up the objective sleep duration of insomniacs and not find much evidence that they sleep less than other people. So I removed the quote.
• The last paragraph of my section about mortality used wording that seemed to imply that Guzey had hypothesized that sleeping 6 hours per night was causally optimal, in the sense that people should sleep that much if they want to have the lowest mortality. Guzey did not actually hypothesize that. He pointed that out and I reworded the paragraph. 

1. ^{^}

   This study looks for publication bias in the literature and says the following about what they found: "Evidence for publication bias was observed for the overall effect and the effect on measures of sustained attention; see Table 3. However, the impact of such publication bias on the effect appears to be minimal as another 75 studies with an effect size <0.0 would have to be added to result in a small overall effect size (g < −0.200)."

   Orwin’s fail-safe N was used to calculate that number.

2. ^{^}

   Note that the β for cumulative days of restricted sleep is negative, providing evidence against Guzey’s hypothesis that cognitive adaptation occurs after several days of restricted sleep, at least in the timespans investigated in the studies included in that meta-analysis.

3. ^{^}

   Importantly, although this meta-analysis included total sleep deprivation studies, the numbers reported in the sentences I quoted are for partial sleep restriction only.

4. ^{^}

   This is a very important caveat. People with mania will feel perfectly comfortable and productive while sleeping very little.