Performance
A circadian neuroscientist explains how biological clocks coordinate sleep, health, cognition, eating, medication, and daily performance.
The body runs on an internal day that would slowly drift away from the real one without a daily correction. According to the author, the strongest correcting signal is light, especially the changes in light around sunrise and sunset. A walk outside at dawn is offered as one way to help that night's sleep.
The author argues that the body works only when the right materials reach the right tissues, in the right amounts, at the right time of day. Timing is part of what makes something work, not a detail. When an action happens can matter as much as what the action is.
The author reports that the same drug can work very differently depending on when it is taken. He cites blood pressure pills taken at bedtime instead of the morning halving the risk of stroke or heart attack. He also cites children's cancer drugs given in the morning instead of the evening, linked to a 4.6 times higher risk of relapse. These are the author's reported findings, not advice to change any treatment.
Since electric light became cheap and common, people have assumed they can do anything at any hour and ignore a body built over 200 million years. Work, exercise and social life keep moving later into the night. The author's verdict is that in doing this we have thrown away an essential part of our biology: sleep.
In the author's account, a change in the brain that leads to mental illness will also disturb sleep, so the two are tied together. He argues the link runs both ways: when sleep disruption is reduced, psychiatric symptoms ease. He also says sleep loss weakens empathy.
The author compares sleep to shoe size: insisting everyone needs the same amount or timing makes no more sense than one shoe size for all. People differ in how long they sleep and when they naturally sleep. A good schedule has to fit the person.
The author holds that what we eat is only part of the story; when we eat matters too. He reports that people who eat late in the evening are at much higher risk of type 2 diabetes and obesity.
The author links living out of step with the body clock to a long list of harms. These include stress hormones, heart disease, weight gain, weaker immunity, cancer risk, diabetes, infertility, and problems with mood and thinking. One mistimed system affects nearly all the others.
The author says that even after years of permanent night work, around 97% of night workers' bodies stay set to daytime. At work they are fighting a whole body that is telling them to sleep. He notes that the World Health Organization classes night shift work as probably cancer-causing.
Exhaustion and working against the body clock wear down judgment, so their costs reach well beyond the tired person. A reviewer reports that the book names this as a likely factor in major industrial accidents. The author adds that the poorest workers bear the heaviest burden, and that employers owe their staff a duty of care.