Tired? We all know the feeling; irritable, groggy, and exceptionally lazy. Chances are you didn’t sleep enough last night...or the past few nights. But what exactly is ‘enough sleep’? And more importantly, can you ever ‘catch up’ on it? While the very function of sleep is still debated by scientists, we do know that it's necessary to function efficiently and productively - after all we spend 24 years of our lifetime sleeping, it’d better be important.
Researchers have tested how much is required each night, by assigning groups of people to 4, 6, and 8 hours of sleep over extended periods of time. After 14 days, those with 8 hours of sleep exhibited few attention lapses or cognitive issues; however, those with 6 or 4 hours of sleep showed a steady decline. In fact, after only 2 weeks, the 6 hour group showed a similar reaction time to a person with a blood alcohol concentration of 0.10% , which is considered legally drunk.
The 4 hour sleepers suffered even more, occasionally falling asleep during their cognitive tests. In both groups, brain function decreased day by day, almost linearly with no sign of leveling off. Scientists have dubbed this cumulative effect as sleep debt. So can we recover from it? After a night or two of little sleep, studies show that the body and brain can fully recover with a few nights of good sleep.
However, with long term sleep deprivation on the scale of weeks to months, the recovery of cognitive function is much slower, requiring many more nights of quality sleep. On the timescale of months to years, it is unknown whether brain function can be fully repaired, or if it causes permanent damage. Paradoxically, with chronic sleep deprivation, your sleepiness or how tired you feel does eventually level off, meaning that you become less and less aware of your objective impairment over time.
So how long should you sleep? Most studies tend to show that 7-8 hours of sleep is the average ideal for humans. Apart from the cognitive issues, individuals who consistently sleep less than 7 hours a night have an increased risk of heart disease, obesity and diabetes - not to mention a 12% higher risk of death. On the flip side, studies have shown that while sleeping more than 8 hours does not impair brain function, it also carries an increased risk of heart disease, obesity and diabetes and a 30% increased risk of mortality!
So too much sleep may also be a bad thing. But variation most certainly exists - and our genetics play a large role! In fact, individuals genuinely unaffected by only 6 hours of sleep were found to have a mutation of a specific gene. When scientists genetically engineered mice to express this gene, they were able to stay awake for an extra 1.2 hours than normal mice.
It turns out these short sleepers have more biologically intense sleep sessions than the average person. Ultimately, while it’s important to know the ideal average of 7-8 hours exists, let your body and brain help you figure out its own needs. After all, no one shoe size fits all.
