Sleep, familiar, yet mysterious, is an essential stage of our daily physiological rhythms—we neglect it at our peril. Every cell in our body contains an independent molecular clock that ticks throughout our lifetime—even in isolation from the outside world—generating what is known as the circadian rhythm.
Thanks to their brilliant molecular genetics experiments on animal models, US scientists Professor Jeffrey Hall, Professor Michael Rosbash and Michael Young helped us understand how this works, and were awarded the 2017 Nobel Prize in Physiology or Medicine for their efforts. The clock is powered by negative feedback circuits cyclically turning on and off specific sets of genes, shared throughout biology, from insects to man. Like an old mechanical wristwatch, the system drifts slowly if left alone and needs an external signal to keep it in sync. The timekeeper that reads this signal is a small region in our brains receiving the measure of external light from our eyes and coordinating internally with the rest of the body through specific hormones and neural signals. This has allowed living things to adapt over millions of years of evolution to the relentless 24-hour cycles of exposure to the sun.
The circadian rhythm also drives most of our physiological processes, modulating up to 50% of the genes in our cells, and exerting enormous influence on our health. Every day, we cycle through a relatively regular pattern, from a more active phase (mainly during daytime) to a rest or sleep phase at night. Other phases may be less obvious but include sequences of distinct physiological changes in our metabolism, cardiovascular and other systems that impact our health. Humans share these daily cycling patterns of physiology with most living beings.
Eyes wide shut
Sleep is one of the more obvious phases in our circadian rhythm. Unfortunately, sleep loss has become a hallmark of the modern professional. Many executives complain, or even brag, about busy schedules, all-nighters, jet lag or excessive partying, that prevent a full night’s rest. The resulting physical exhaustion should not be taken lightly. The US National Academy of Medicine has issued national guidelines against sleep deprivation of medical professionals and trainees. Airlines take the sleep of their crew seriously. And we all know the dangers of driving when tired.
‘Short term sleep deprivation not only makes us feel like a total wreck, we also underperform in tests of cognitive ability, memory retention, decision taking and other essential professional capabilities.’
But what happens when we don’t get enough sleep? At its most extreme, complete sleep deprivation has been shown in controlled experiments with animals to be lethal. The available data for humans, though sparse for obvious reasons, predicts the same outcome. More pertinent to our everyday performance, partial sleep disruptions and repeated shortened sleep periods are more harmful than most people think. The short term impact includes not only feeling like a total wreck, with headaches, irregular body temperature, gastrointestinal symptoms and more, but also results in severe underperformance in tests of cognitive ability, memory retention, decision taking and other essential professional capabilities. While the amount of sleep needed varies between people, and it is possible to make up for occasional lost sleep by resting more the following day, this kind of flexible sleep accounting has its limits.
The research data is discouraging. Our metabolism goes off, leading to diseases such as obesity and diabetes. Hypertension sets in, raising the risk of acute heart failure or chronic heart disease. Not only is a sleep-deprived brain unable to memorise and function at its peak, it also cannot clear endogenous waste products which can accumulate and lead to Alzheimer’s disease. Moreover, long term sleep deprivation, even if partial, is correlated with increased incidence of cancer.
Our bodies simply must go through their circadian rhythms in as constant a pattern as possible to maintain healthy function. When it doesn’t, we underperform at work and shave years off our lives.