British-American neuroscientist Matthew Walker’s Why We Sleep: Unlocking the Power of Sleep and Dreams (2017) provides an in-depth exploration of the science of sleep health. Walker argues that sleep loss is an epidemic and one of the most serious public health issues of the 21st century. Drawing from a wealth of data and scientific studies, including his own innovative scientific breakthroughs during his time as a professor at the University of California-Berkeley, Walker illustrates the extensive damage sleep deprivation does to all major brain and bodily functions. His arguments also draw from his tenure as a sleep consultant for several large companies and sports organizations, including Google, Fitbit, NBA, NFL, British Premier League football teams, and Pixar Animation.

Walker’s goal is to reunite humankind with sleep, but to do this he recognizes that he must first demystify sleep, detail the benefits of sleep and the costs of sleep loss, explain the power of dreams, unpack how our modern environment makes obtaining a good night’s sleep challenging, and the societal costs of insufficient sleep. Accordingly, the book is divided into four main parts. Though the narrative is overarching, Walker notes that each chapter can be read on its own and out of order.

In Part 1, Walker provides a detailed view of what sleep is and is not, the evolutionary context of sleep, and how sleep changes across the human lifespan. Sleep is not unique to humans but universal across animal species, but humans are the only known animal who willingly deprive themselves of this biological necessity. The circadian rhythm and sleep pressure (adenosine) control humans’ sleep-wake cycle, which was shaped by Homo sapiens evolution in eastern Africa. Humans generate two different phases of sleep: NREM (non-rapid eye movement) and REM sleep. Each phase serves life-sustaining but different body and brain functions. Sleep also plays a critical role in brain development during early childhood and adolescents but deteriorates with age.

Part 2 moves on to discuss the astonishing benefits of sleep for the brain and body and how and why sleep deprivation leads to ill health, disease, and a shortened lifespan. Sleep, and particularly eight hours of nightly sleep, helps the brain facilitate memory consolidation, retention, and retrieval. Inadequate sleep impacts concentration, plays havoc with human emotions, makes individuals more forgetful, and increases the risk of developing Alzheimer’s disease. Moreover, sleep disturbances increase the risk of obesity, diabetes, stroke and heart attacks and cancer development, and impair the immune and reproductive systems.

Part 3 scientifically explains the fantastical world of dreams. Walker starts with emphasizing that dreams are not by-products of REM sleep but serve critical functions of their own. In fact, dreams have therapeutic, emotional processing, problem-solving, and creative functions. Dreams inspire human ingenuity and are the primary reason that we are the only animal to have solved the challenge of the periodic table of elements or traveled beyond Earth. The closing focus of this segment is on dream control, which perhaps is the next phase in humanity’s evolution.

Finally, Part 4 first examines the impact sleep deprivation has on individuals. Walker discusses several sleep disorders, supporting his claim that few other areas of medicine offer a more astonishing or troubling number of disorders than those related to sleep. Next, he turns to factors, many of which are a product of our modern environment, that impact sleep. These range from technological devices like smartphones and laptops to alcohol to climate-controlled bedrooms. To overcome sleep disturbances, millions of people turn to sleeping pills. Walker strongly counsels against their usage and offers other effective non-drug alternatives. Walker then broadens his discussion to the detrimental impacts of sleep loss on society, which include costs to GDP, collective shame when used as a form of torture, creation of a generation of disadvantaged children, and poorer healthcare quality. In this section’s closing chapter, Walker offers several intervention opportunities that individuals, industry and education leaders, and government officials and policymakers can implement to help overcome the sleep epidemic.

The data presented throughout Why We Sleep reaffirm repeatedly that there are no benefits to sleep loss. Yet, despite the enormity of the public health challenge at hand, Walker remains fiercely optimistic that humanity will reconnect with sleep.