Do you think sacrificing sleep to get more work done makes you – or your employees – more productive? Think again. Although you may not be able to think very clearly.
A landmark study published in 2003 showed that sleeping for six hours or less every night destroyed the cognitive performance of healthy adults in just two weeks.
Cognitive performance includes processes such as perception, memory, learning, attention, decision making, problem solving, creativity, and communication. It’s a crucial component of mental health. In fact, I can’t think of any aspect of health and wellbeing that is more important to work and life. And yet, it rarely – if ever – features in the discussions around employee mental health.
As it turns out, like all other aspects of health, cognitive performance is largely determined by eat, move, and sleep habits. Here, we’re going to explore the cognitive impact of sleep, or rather lack of sleep.
The 2003 study found that sleeping for four to six hours a night for two weeks:
- Progressively eroded cognitive performance, contradicting the commonly held belief that humans can mentally adapt to chronic sleep restriction
- Eroded cognitive performance to a similar degree as one to two days of total sleep deprivation
- Did not increase sleepiness after the first few nights, which is probably why such sleep restriction is widely practised
The study included 48 healthy adult subjects, aged between 21 and 38 years. They were randomly allocated to one of four sleep conditions:
- Eight hours of sleep a night for 14 nights (8-hour condition);
- Six hours of sleep a night for 14 nights (6-hour condition);
- Four hours of sleep a night for 14 nights (4-hour condition); or
- No sleep at all for three nights (no sleep condition)
For the duration of the sleep conditions (and three ‘normal’ nights either side) the subjects lived in a sleep laboratory, so all relevant variables were tightly controlled. While awake, the cognitive performance – alertness, working memory, and accuracy and speed – and sleepiness of the subjects were measured every two hours.
The results were, quite literally, mind blowing.
As you might expect, the cognitive performance of the subjects in the 8-hour condition didn’t change. In comparison, those in the 6-hour condition suffered declines in cognitive performance every day, which accumulated over time. The 4-hour condition subjects fared even worse. It’s safe to assume that, had the experiment gone beyond two weeks, the cognitive decline would have continued.
The cumulative impact on cognitive performance after two weeks was equivalent to that of 24 hours with no sleep at all (for the 6-hour condition) and 48 hours with no sleep at all (for the 4-hour condition). Many of you will have pulled an ‘all-nighter’ at some point, so you will have experienced the crushing impact on brain function of being awake for 24 hours. Well, people who sleep for six hours a night are in that same state (or worse). All the time.
Except they don’t realise it because they don’t feel sleepy. After the first few nights of sleep restriction, the subjects in the 6-hour and 4-hour conditions didn’t feel any sleepier, even while their cognitive performance continued to decline day after day. In fact, by the end of the two-week period, when cognitive performance was at its worst, subjects in the 6-hour and 4-hour conditions reported feeling only ‘slightly sleepy’. And there was no difference in the sleepiness ratings between the 6-hour and 4-hour conditions, despite cognitive performance being substantially worse in the 4-hour condition.
Imagine how poorly your brain would function after 24 or 48 hours without sleep. Now imagine you didn’t realise.
Cognitive performance – how well the brain works – is one of the most important determinants of employee wellbeing and performance. And, as we’ve seen here, consistently getting less than eight hours of sleep destroys our ability to process, think, and react effectively.
If you want a company full of people on top of their mental game, you must enable, encourage, and empower your employees to get at least eight hours of sleep every night. It’s business critical.