One of the professors at Edinburgh Medical School, where I was taught from 1970-76, was a world expert on sleep, but I remember hearing little about sleep at medical school. We were taught about sleeping pills, and I remember routinely prescribing them for patients undergoing surgery the next day—with no understanding of the damage I was doing. In my 25 years at The BMJ I remember publishing little on sleep, although we did publish an ABC of Sleep Disorders, with the emphasis on the disorders. Generally, like most doctors, I thought little about sleep. Now I read in Matthew Walker’s book Why We Sleep: The New Science of Sleep and Dreams that: “ [The] silent sleep loss epidemic is the greatest public health challenge we face in the twenty-first century in developed nations.” He perhaps forgot climate change, but he makes a strong—if not wholly convincing—case to support his dramatic claim.

His core argument about the public health challenge is that we all need at least seven and preferably eight hours sleep a night because sleep is vital for many functions of the brain and body, including memory, problem solving, attention, immune function, growth, and the effective and efficient functioning of most of our organs. Lack of sleep leads to dementia, raised blood pressure, heart disease, stroke, cancer, road traffic and other injuries, and proneness to infection—in other words to all the commonest causes of morbidity and mortality. Yet many people in the developed world are not getting seven to eight hours sleep a night, and crucially he shows that you cannot catch up on lost sleep—sleeping late at the weekend will not undo the damage done during the week. Worse, we have a culture that almost sees sleep as for wimps, and we admire people like Margaret Thatcher and Ronald Reagan (both of whom succumbed to dementia, points out Walker) who supposedly slept only four or five hours. Walker shows that people who can sleep so little and not suffer long-term damage are vanishingly rare.

All of biology is ultimately about evolution, and humans have evolved over two million years to sleep eight hours a night. Walker presents evidence from hunter-gatherers of how they sleep eight hours a night, although often in two parts. Sleep is clearly important, and it is also extraordinary: Walker mimics a paediatrician talking to parents of a new born baby: “From this moment forth, and for the rest of your child’s entire life, he will repeatedly and routinely lapse into a state of apparent coma. It might even resemble death at times. And while his body lies still his mind will often be filled with stunning, bizarre hallucinations. This state will consume one-third of his life and I have absolutely no idea why he’ll do it, or what it is for. Good luck!” Walker makes us think that this bizarre state must have some vital function and teases the medical profession for paying little attention to the importance of sleep.

Medicine, with its emphasis on disease and malfunction, has also neglected to a lesser degree diet and physical activity, and I suspect that few doctors would describe sleep as a pillar of good health, but Walker goes further: “I was once fond of saying, ‘Sleep is the third pillar of good health, alongside diet and exercise.’ I have changed my tune. Sleep is more than a pillar; it is the foundation on which the other two health bastions sit. Take away the bedrock of sleep, or weaken it just a little, and careful eating or physical exercise become less than effective.”

Walker, a scientist rather than a clinician, is at his best explaining the functions of sleep, although we still have a long way to go with understanding all the effects of sleep. His book reminded me of Daniel Kahneman’s world-changing book Thinking Fast and Slow in that much of the evidence comes from psychological experiments performed in sleep laboratories. To be fair to my teachers at medical school most of the research has been conducted since I left medical school. I particularly liked Walker’s sculpture metaphor for explaining how REM (rapid eye movement) sleep and NREM (non-REM) sleep are essential for memory: NREM, which predominates at the beginning of sleep, moves the great clumps of clay (the day’s learnings) into memory and then REM sleep, which predominates later, refines and shapes the clay to make the memories.

The book even manages to cast light on the particular importance of dreams not just the REM sleep during which they occur. Ingenious experiments have shown that dreams have therapeutic, problem solving, and creative functions.

There is epidemiological evidence in the book, but I’d have liked more of that to be wholly convinced of Walker’s assertion that lack of sleep is our leading public health problem. I think that anybody who reads his book will be convinced of the importance of sleep and will make sure that they do all they can to get eight hours’ sleep a night, but there are many forces—including work habits and requirements, electric light, noise, electronic gadgets (particularly those, the majority, powered by blue LED lights), alcohol, caffeine, mass entertainment, and a culture that doesn’t grasp the importance of sleep—that work against getting eight hours sleep every night. (I reflect on how little the harmful effects of sleep disruption as opposed to pollution have featured in the arguments over a third runway at Heathrow—I wake most mornings to the sound of planes heading towards Heathrow.)

An individual, particularly  a retired one like me, can do something to try and ensure eight hours sleep a night, but many social forces work against it. Walker chastises school systems that oblige adolescents to attend school at 7.30am for failing to understand that adolescents’ diurnal rhythm runs some three hours behind those of adults, meaning that getting up at 6am each day to get to school by 7.30am feels like getting up at 3am for an adult. He also criticises medicine for its long-hours culture, meaning that doctors make many more errors.

This book, a best-seller, has changed my thinking greatly. I wonder if it will manage to have a broader effect on society. I hope so.

PS. A fun quote from the book:

“Last night, you became flagrantly psychotic. It will happen again tonight. Before you reject this diagnosis, allow me to offer five justifying reasons. First, when you were dreaming last night, you started to see things that were not there— you were hallucinating. Second, you believed things that could not possibly be true— you were delusional. Third, you became confused about time, place, and person— you were disoriented. Fourth, you had extreme swings in your emotions— something psychiatrists call being affectively labile. Fifth (and how delightful!), you woke up this morning and forgot most, if not all, of this bizarre dream experience— you were suffering from amnesia. If you were to experience any of these symptoms while awake, you’d be seeking immediate psychological treatment.”

Richard Smith was the editor of The BMJ until 2004.