If you've ever gone without sleep for an extended period, you will know it isn't exactly a good idea. Even one night of broken sleep can cause problems the next day - and there can be few things worse than not getting enough shut-eye for weeks on end.
But while lack of sleep is undoubtedly bad for you, the jury's out as to how bad. We know it can cause a litany of health problems, both on a short and long-term basis. What is harder to determine is - can it kill you?
Mercifully for insomniacs who don't need another thing to worry about, the answer seems to be no. According to Professor John Groeger of Nottingham Trent University, deaths from sleep deprivation are likely to occur only indirectly.
"Nobody dies from lack of sleep alone, and I suspect nobody has," he says. "However, being sleep-deprived increases absolutely every other risk we face. You are more likely to die when driving if sleep-deprived than not, and the risk of a small amount of alcohol when driving is far greater if you haven't slept or slept well. Slips trips and falls are all more likely when lacking sleep, not to mention the stroke, hypertension, type 2 diabetes, obesity, risk of suicide, etc."
Some reported cases
True enough, most purported deaths from sleep deprivation can be traced to other causes. In 2012, a Chinese football fan reportedly died of exhaustion after staying up for 11 nights in a row to watch every game in Euro 2012 championship. Two years later, the same thing happened when a different Chinese football fan stayed up for days to watch the World Cup.
However, in both these cases the cause of death wasn't clear-cut. In the first case, the man is thought to have died from the combined effects of alcohol, tobacco and sleep deprivation. In the second, the doctors cited a possible heart attack as the causative factor.
We know there is one condition associated with lack of sleep which can be fatal. With fatal familial insomnia, a prion disease of the brain, patients progress from complete insomnia to dementia and die between seven and 36 months after onset. However, it is a degenerative brain disease and also affects other body regulation functions such as temperature and heart rate regulation. So even here, it's not insomnia alone which causes the problem.
Luckily, this disease is extremely rare. It has only been found in about 40 families worldwide and shouldn't be a cause of concern for the average person.
How long can you go without sleep?
In fact, it seems that people can go without sleep for a surprisingly long time. If you watched Channel 4 during the reality TV heyday of the early 2000s, you may remember a show called Shattered, in which participants stayed awake as long as possible in order to win a cash prize. (The winner, Clare Southern, managed a gruelling 178 hours.)
Perhaps the most famous sleep deprivation study came in 1964, when a 17-year-old boy, Randy Gardner, voluntarily went 264 hours (11 days) without sleep. Although he was hallucinating by day 5, he seemed to suffer no long-term ill effects, and was sleeping normally within a few nights.
Since then, there have been a number of attempts to break this record, including a reported 449 hours by Maureen Weston in 1977. However, the Guinness Book of Records has stopped certifying these attempts so as not to encourage people.
This means the true outer limits of endurance aren't known. And in fact, research into sleep deprivation generally has been stymied by ethical issues. You certainly couldn't ask human subjects to stay awake until they dropped dead.
Animal experiments do suggest death by sleep deprivation is possible. In the 1980s, the University of Chicago conducted a series of experiments on rats, and found that after 32 days of sleep deprivation all the rats had died.
However, in practical terms it seems the brain has a defence mechanism against prolonged sleeplessness. Stay awake for long enough, and you will be highly prone to microsleeps - temporary, unintended episodes of unconsciousness that may be just a fraction of a second long. (While microsleeps do serve a purpose, they are also part of the reason why you shouldn't drive when tired.)
Consequences of lack of sleep
So how does going without sleep actually affect your health? Groeger points out that very little gets better when we lose sleep.
"A loss of just an hour a night over a few nights in a row will gradually affect your mood, physical health and how well you perform," he says. "The effects of this sustained shortened sleep are evident in your hormones, heart rate, appetite and digestion. Your resistance to bugs reduces, and if you were ill to begin with, your recovery slows. These changes are slight at first, but accumulate over time."
Unfortunately, many of us are in this state much of the time (whether due to insomnia, a busy life, or small children). Although we may attempt to compensate with caffeine, sugar etc, the only real antidote to sleep loss is sleep itself. (You don't need to put back all, or even most, of what you've lost.)
Over the long term, the effects of sleep deprivation are compounded, with chronic sleep loss playing a clear role in a number of physical diseases and mental health conditions.
"We have known about this for the last decade or so but more recently research has begun to show how resistance to, and recovery from, infection or inflammation is massively affected by chronic sleep loss," says Groeger. "Again, most of these effects are reversible, but doing so requires far more than a few decent nights' sleep, because of the physical damage which the body or brain has endured - hence why lifestyle changes are also part of the recovery process."
While the amount of sleep you need is highly individual - it will depend on your age, sex, health, lifestyle, etc - if you're not getting enough, you will know about it. If prolonged lack of sleep is a problem, see your doctor, who will be able to give you an evaluation and may refer you to a sleep clinic if necessary.
After all, lack of sleep may not kill you, but it's worth addressing as soon as it starts to affect your quality of life.