It stands to reason that getting a few hours of shut-eye a night is better than going without sleep altogether, but the science says otherwise. In a US-based study, participants who'd slept for 6 hours a night over two weeks were found to be just as badly affected as those who'd gone without sleep for two nights in a row.
The 48 volunteers were tested every 2 hours (while awake) to assess cognitive performance and reaction time; they were also asked to answer questions on their mood and how sleepy they felt. By the end of the experiment, not only were the slightly sleep-deprived people at a similar level to those who'd gone without sleep, they also didn't know it – they thought they were still functioning as normal.
This doesn't mean if you stay up all night tonight it's the same as getting 6 hours of sleep, but it does indicate that the cumulative effects of getting less shut-eye than you should will eventually add up to the equivalent of sleepless nights as far as your brain is concerned. That's something to consider when you're up until late watching Netflix or playing one more level on your video game of choice.
"It appears that even relatively moderate sleep restriction can seriously impair waking neurobehavioral functions in healthy adults," the team from the University of Pennsylvania concludes in the report, published in the journal Sleep.
"Sleepiness ratings suggest that subjects were largely unaware of these increasing cognitive deficits… sleep debt is perhaps best understood as resulting in additional wakefulness that has a neurobiological 'cost' which accumulates over time."
Even as the cognitive performance of the 6-hour group was deteriorating, these participants weren't reporting much change in how sleepy they felt – certainly not as much as those who went one or two nights without sleep altogether. So do we kid ourselves about how much sleep we need or how sleepy we feel?
As Jill Duffy from Fast Company explains, we're also very bad at estimating how much sleep we're actually getting every night, which further complicates matters. One recent study suggests that we tend to overestimate the amount of time we've spent asleep by almost an hour a night: if you think you're getting 7 hours of sleep a night, you might only be getting 6.
Additionally, the researchers found that the effects on cognitive performance lasted through the whole of the working day, while those participants who got 8 hours of sleep every night showed none of the adverse effects noticed in the other groups.
It's been well-established that a lack of sleep can have a whole host of detrimental effects, but the cumulative effect of skimping on a few hours of slumber each night hasn't been as comprehensively explored. While the sample size of this particular experiment is very small, the results certainly warrant further investigation.
Something worth bearing in mind the next time you reach out for the snooze button.