Fatigue can also adversely affect the workplace, with repercussions on both performance and leadership. Barnes was the first to examine how sleep-deprived bosses are more likely to mistreat their employees through hostile verbal and non-verbal behaviour: “They go into work with less self-control and they’re more likely to engage in what we call ‘abusive supervision’,” he says. (Read more from BBC Future about why burnout happens and what to do about it.)
Worse still, fatigue can have devastating outcomes — in the UK, tiredness is the root cause of 20% of all accidents on major roads. Human error linked to fatigue or sleep loss has also been implicated, along with other factors, in numerous man-made disasters, including the Challenger Space Shuttle accident and the Exxon Valdez oil spill. “Fatigue in oil and gas [extraction], both onshore and offshore, has resulted in significant catastrophes, the loss of lives, economic issues, and environmental issues that we still suffer from,” says Ranjana Mehta, a professor of industrial and systems engineering at the University of Wisconsin-Madison, Madison, who studies occupational fatigue.
But getting sufficient shuteye is only one part of the equation. Quality matters too, if not more. “Getting fewer hours of solid sleep is better than more hours of sleep, but interrupted sleep,” says Whittemore. “You feel much less refreshed if you have interrupted sleep.”
That’s partly because when we sleep, our brains power down extraneous processes. The resting neurons create space for cerebrospinal fluid, which usually surrounds the brain, to flood in and clear out accumulated debris, such as the sticky beta-amyloid plaques that are usually associated with Alzheimer’s disease. It’s a sort of waste-clearance system scientists call the glymphatic system. “If you have disrupted or dysfunctional sleep, it disrupts that whole balance,” says Whittemore. “So there aren’t as many toxins being cleared from your brain.”
Interestingly, our glymphatic systems work best at the same time every day, says Daniel Jin Blum, a sleep psychologist and research assistant professor at New York University Shanghai. “So if you get the same amount of deep sleep at your regular time versus shifted eight hours later, the ability to flush out toxins is significantly compromised.”
This means that when we get our shuteye is important. Syncing sleep with our natural circadian rhythms – the brain’s 24-hour internal clock that regulates the cycle of alertness and sleepiness – gives rise to the best-quality rest. This explains why shift work is often associated with poor health outcomes, ranging from heartburn to diabetes.
“Among other things, if you get that same eight hours of sleep, but not during the regular circadian period, you get almost no REM sleep and you’re not really reaping the benefits,” says Blum, referring to the fourth and final stage of our sleep cycle that’s characterised by rapid eye movements, where we typically dream, strengthen neural connections, and process emotions from the day. Too little or dysregulated REM sleep has been linked with depression, dementia, Parkinson’s disease, and other cognitive issues.
Myriad reasons
Given the pervasive effects of poor-quality sleep on our health, relationships, and work, it’s important to try and unearth the root of all this misery. When patients complain of persistent fatigue, the first thing Adam does is rule out any medical causes.
Blood tests can sometimes be useful in pinpointing thyroid disorders or an imbalance of oestrogen and other hormones – conditions that are frequently linked with feelings of fatigue, especially in women.
Tests can also reveal if you’re lacking certain nutrients like vitamin B12, folate, and D; or minerals such as iron and magnesium. “Nutrient deficiency plays a substantial role in contributing to fatigue,” says Geir Bjørklund, who founded the Norwegian nonprofit Council for Nutritional and Environmental Medicine. “Essential nutrients, including vitamins, minerals, and dietary components, are crucial for various physiological processes, including energy metabolism,” he says.
