While it is good to be skeptical, the book really goes in depth and makes a compelling case. I also believe sleep is one of those areas that it is better to err on the side of getting the recommended amount. “If sleep does not serve an absolutely vital function, then it is the biggest mistake the evolutionary process has ever made.” - Dr. Allan Rechtschaffen.
They are all observational studies, usually with small cohorts. Same problem with nutrtitional science and psychology. History tells us again and again these results are biased, unduly influenced by the investigators and often overturned (eg Thinking Fast and Slow).
