Hi, I'm the author of that critique.

>Point 1: the chart bottoms out at 7, which falls within the range the book recommends. I'm fairly sure he recommends 7-9, and that the required amt varies from person to person. Another thought I had: metabolism and longevity go hand and hand. I mean, I just read a brand new paper from George Church's Harvard lab, showing that they reversed several chronic ailments in mice by inserting FGF21, which regulates glucose levels. And sleep absolutely regulates metabolism. Personally, I'm keeping my ears perked up when it comes to metabolism/circadian rhythms/homeostasis, etc.

The point you're making has nothing to do with the point I'm making in the relevant section. I take issue with Walker writing "the shorter your sleep, the shorter your life span". You seem to have missed this part entirely. If you say that the book recommends 7-9, feel free to quote the book because it definitely seems that he strongly advocates at least 8 hours. Example: as I showed in section 5, Walker takes 7-9 hours recommendation from the National Sleep Foundation and then falsely claims that they recommend 8 hours of sleep.

>Point 2: Depression is an incredibly complicated topic. It is a psychological construct, the net result of thousands and thousands of genes, filtered through a modern technological world, and then filtered through inventories, interviews, and assessments. For this reason, I am not at all surprised that Guzey was able to find studies that suggest that sleep deprivation might have some benefit for some people. I would HIGHLY recommend this new, open-access Nature review paper covering the genome wide studies on depression: https://doi.org/10.1038/s41398-019-0450-5. Its almost not worth pitting a complex phenotype like depression against another complex behavior like depression. But what the hell, let's brush with broad strokes: the significant genetic variants associated with depression have to do with regulating homeostasis (eg sirtuins). So I would not be surprised if good sleep is at least correlated with low levels of depression.

You missed the point I was making entirely. Walker wrote that there are no biological functions that do not benefit from a good night's sleep. I point out that this is false, as sleep deprivation therapy is a safe, effective, and a very-well studied treatment for depression.

>Point 3: I know almost nothing about FFI, but we have kept mice awake, and they do eventually die. I'm pretty sure humans would die too, but ethics precludes us from performing such a study.

You missed the point I was making entirely, again. Walker wrote that FFI demonstrates that lack of sleep kills people. I pointed out that saying that is completely false. What relation do mice have to the point I was making?

>Points 4&5: This is just fussing about Walker's writing and WHO. I'll have to agree with Guzey that Walker's citations and consistency are often weak. And I honestly couldn't care less about WHO. But I'm pretty confident that sleep quantity has declined with time across the world. I remain curious about the connections between light and circadian rhythms (I think retinal cells go straight to the superchiasmatic nucleus, the circadian rhythm controller). Also, sugar is a thing in the modern world.

Points 4&5: this again has very little relationship with what I was writing. In section 4, I pointed out that Walker has seemingly invented a sleep loss epidemic and attributed it to the WHO. This is not just an issue with citations. In section 5, I pointed out that Walker misrepresents National Sleep Foundations sleep guidelines, saying that they recommend 8 hours of sleep, while in reality they recommend 7-9 hours of sleep.

For readers of this exchange: if you're still unsure how serious my concerns with the book are, the clearest example is provided in section 18, where I show deliberate data manipulation by Walker. He simply edited out the part of the graph that contradicted his argument in the book: https://guzey.com/books/why-we-sleep/#appendix-what-do-you-d...