Why We Sleep

Summary

Why We Sleep by Matthew Walker, PhD (2017) is the most-cited popular-science sleep book of the last decade and the one most likely to walk into a sports medicine clinic in the hand of a worried patient. The book is built around four parts — how sleep works, why you need it, what dreams are for, and what sleep means for society — and closes with twelve practical tips for better sleep. Walker's underlying case is largely correct: adults 18 to 64 should sleep at least 7 hours per night on a regular basis, with 7 to 9 hours as the recommended range, and chronic short sleep is one of the most consistent dose-response relationships in the entire medical literature. His framing of specific quantitative claims is sometimes overstated, and a careful 2019/2025 critical review by Alexey Guzey documents specific overstatements on mortality, cancer risk, and WHO prevalence that the popular narrative should not repeat uncritically.

About

Matthew Walker is a professor of neuroscience and psychology at the University of California, Berkeley, and the founder and director of the Center for Human Sleep Science. His research has helped shape the modern clinical conversation about sleep's role in memory, emotional regulation, metabolic health, immune function, and cardiovascular risk.

Why I recommend it

Walker's case for sleep converges with the sports medicine evidence I bring into clinic: extending sleep improves performance, and chronic short sleep roughly doubles youth-athlete injury risk. The book is the right next read for the patient who has finished Sleep Basics and wants the broader case for sleep as a foundation of health.