Matthew Walker's book Why We Sleep brought to mainstream attention a body of research that sleep scientists had been accumulating for decades: there is no major system in the human body whose function is not significantly impaired by inadequate sleep. The immune system, the cardiovascular system, metabolic regulation, cognitive function, emotional regulation, reproductive hormones, and physical repair all depend on adequate sleep for their normal function. Claiming to do fine on five or six hours of sleep per night is, in almost all cases, an inaccurate self-assessment; the research shows that people chronically deprived of sleep are poor judges of their own impairment.
What Happens During Sleep That Cannot Happen Otherwise
Sleep is not simply rest; it is an active biological process involving multiple distinct phases that perform specific functions. Slow-wave sleep drives growth hormone release that mediates physical repair and immune function. REM sleep consolidates emotional memories, processes emotional experiences, and maintains the emotional regulatory systems that prevent mood disorders. Glymphatic clearance, the brain's waste removal system that clears amyloid beta and other neurotoxic proteins associated with Alzheimer's disease, operates primarily during sleep and is substantially reduced when sleep is disrupted. These functions cannot be performed at reduced efficiency during waking; they either happen during sleep or they do not happen.
Sleep and Every Other Health Goal
Sleep deprivation directly undermines every other health investment. Inadequate sleep reduces anabolic hormone production, reducing the benefit of resistance training. It elevates ghrelin and reduces leptin, increasing appetite and food intake while impairing the ability to resist high-calorie foods. It impairs the glucose metabolism that makes dietary carbohydrate management possible. It reduces exercise motivation and tolerance and increases injury risk. It impairs the emotional regulation that makes social relationships function well. Anyone pursuing health goals while tolerating chronic sleep deprivation is working against their own investment.
The Busyness-Sleep Trade-Off
The cultural prestige of busyness and the normalisation of sleep deprivation in professional culture has created a widespread belief that sleep is negotiable and that its sacrifice is a sign of dedication. The research does not support this. A study by Harriet Agerbo and colleagues found that sleep deprivation impairs performance on complex cognitive tasks as significantly as a blood alcohol level above the legal driving limit. Performing cognitively demanding work in a sleep-deprived state is not productive; it is accurately described as performing drunk.
Practical Steps to Make Sleep a Priority
Making sleep a priority requires treating it as a non-negotiable commitment rather than a variable to be adjusted when other commitments expand. This means: setting a consistent wake time and using it to work backward to a consistent bedtime; treating pre-sleep time as preparation for sleep rather than additional productive hours; managing light exposure, particularly blue light from screens in the two hours before sleep; maintaining a cool sleeping environment; and, importantly, resisting the social normalisation of sleep deprivation by declining the cultural mythology that successful people sleep less.