This was one of the most thought-provoking posts I read this month. Mostly because I spent a really large number of hours of my life sleeping, and also significantly increased the amount that I've been sleeping over the past three years, and this has me seriously considering reducing that number again. 

The opening section of the article: 


Matthew Walker (a) is a professor of neuroscience and psychology at the University of California, Berkeley, where he also leads the Center for Human Sleep Science.

His book Why We Sleep (a) was published in September 2017. Part survey of sleep research, part self-help book, it was praised by The New York Times (a), The Guardian (a), and many others. It was named one of NPR’s favorite books of 2017. After publishing the book, Walker gave a TED talk, a talk at Google, and appeared on Joe Rogan’s and Peter Attia’s podcasts. A month after the book’s publication, he became (a) a sleep scientist at Google.

On page 8 of the book, Walker writes:

> [T]he real evidence that makes clear all of the dangers that befall individuals and societies when sleep becomes short have not been clearly telegraphed to the public … In response, this book is intended to serve as a scientifically accurate intervention addressing this unmet need [emphasis in this quote and in all quotes below mine]

In the process of reading the book and encountering some extraordinary claims about sleep, I decided to compare the facts it presented with the scientific literature. I found that the book consistently overstates the problem of lack of sleep, sometimes egregiously so. It misrepresents basic sleep research and contradicts its own sources.

In one instance, Walker claims that sleeping less than six or seven hours a night doubles one’s risk of cancer – this is not supported by the scientific evidence. In another instance, Walker seems to have invented a “fact” that the WHO has declared a sleep loss epidemic. In yet another instance, he falsely claims that the National Sleep Foundation recommends 8 hours of sleep per night, and then uses this “fact” to falsely claim that two-thirds of people in developed nations sleep less than the “the recommended eight hours of nightly sleep” – a myth that spread like wildfire after the book’s publication.

Walker’s book has likely wasted thousands of hours of life and worsened the health of people who read it and took its recommendations at face value.

Any book of Why We Sleep’s length is bound to contain some factual errors. Therefore, to avoid potential concerns about cherry-picking the few inaccuracies scattered throughout, in this essay, I’m going to highlight the five most egregious scientific and factual errors Walker makes in Chapter 1 of the book. This chapter contains 10 pages and constitutes less than 4% of the book by the total word count.

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I stopped taking the book seriously when I reached Walker's suggestion that teenagers might have a sleep cycle offset from adults because "wise Mother Nature" was giving them the chance to develop independence from the tribe, in a group of their peers, and that this was an important stage in societal development of a human.

If one *must* find an evo-psych explanation for this phenomenon, surely "we need people guarding the camp at more hours of the day" is simpler and less ridiculously tenuous. (Though this still has precisely the same "I could have explained anything with this" flavour that most popular evo-psych does.)

(removed this comment)

Yes, this just-so-story is suspicious, especially because it's not "just so"--if there were such strong selection for variability, wouldn't you expect full coverage of the night? Some people could go to bed at four and others could wake up at three. As far as I know this does not generally happen (in the absence of electric lighting) and hence the dangers of having everybody asleep at once must be manageable.

Alas, according this FB ad I just saw, the guy really took off.

Walker probably feels justified in exaggerating or is simply biased in his investment of accuracy-checking effort) akin to climate scientists - feeling the public won't update its policy as close to the optimal setting unless they lie.

That is a strategy whose defects are proverbial.

I don't understand why this is downvoted. I don't perceive this comment to be defending the algorithm it is ascribing to Walker, just assigning it higher probability. 

Maybe the claim that climate scientists are liars? I don't know if it's true, but if I knew it were false I'd definitely downvote the post...

Author advocates biphasic sleep totaling 6.3hr/day.

Author claims doesn't support 'smaller testes size for men who sleep less'. It does.

Still, I appreciate that he helped me repair some erroneous beliefs I picked up from Walker's book.

I'm the author of this essay. I don't believe your characterization of it is accurate.

1. You write:

Author advocates biphasic sleep totaling 6.3hr/day.

I don't remember "advocating" biphasic sleep. I link to people I know who were able to adjust to it and I describe my personal experience. In fact, in the essay's conclusion I write:

If you take one thing away from this entire essay, remember this: as long as you feel good, sleeping anywhere between 5 and 8 hours a night seems basically fine for your health

which contradicts your assertion.

2. You write:

Author claims doesn't support 'smaller testes size for men who sleep less'. It does.

You add quote marks as if you're quoting my essay. I never wrote that this paper doesn't support 'smaller testes size for men who sleep less'. I wrote: "It does not support either of Walker's claims" Here are Walker's claims:

Men who sleep 5 hours a night have significantly smaller testicles than those who sleep 8 hours or more. [from his 2017 talk at Google)


Men who sleep 5 hours a night have significantly smaller testicles than those who sleep 7 hours or more. [from his 2019 TED Talk]

The paper in question finds a correlation between sleep and testicle size. Walker says that the difference between those sleeping 5 and those sleeping 8 hours or more (or 7 hours or more) is "significant", by which he clearly means statistical significance. The paper never examines whether the difference between those two groups is statistically significant. It is true that it found a significant correlation. The paper however does not support either of Walker's claims.

Anticipating comments that say that I'm nitpicking: the testicles thing is indeed nitpicking and it's not important. I included it in one of the last appendices of the essay, mostly out of curiosity at the fact that Walker repeats the exact same phrases word for word in different talks but his numbers change in the process.

Finally, (even though I believe their reading of my essay is wrong), I'm glad that both of the OP's concerns regard things he found in appendices to the essay and not in any of the main parts it.