So far, we've spoken about all of the wonderful benefits that sleep provides, but how much sleep should we actually be getting? [Sleeping with Science] (Music) For the average adult, the current recommendation is somewhere between seven to nine hours of sleep a night. And what we've been finding from large-scale epidemiological studies is that, using that reference point of seven to nine hours, once you start to drop below that, your mortality risk actually starts to increase. In fact, the Center for Disease Control in the United States, or the CDC, they stipulate a minimum of seven hours of sleep a night for the average adult. In other words, the shorter your sleep, the shorter your life. But it turns out that it's not quite a linear relationship as you would expect. It's not as though the more and more that you sleep, the lower and lower your mortality risk is. In fact, something strange happens. Once you get past nine hours, you actually start to see a rise back up in mortality risk, which seems rather strange and peculiar. And scientists have actually put forward at least two different explanations. The first is that, if you look at those studies, it may be that individuals are suffering from significant disease and illness. When we become infected, or we have disease, typically, we try to sleep longer, we stay in bed longer. So in other words, it was the unmeasured disease and sickness in those studies that was triggering a response in those individuals to try and sleep more. That's one explanation. The second possible explanation is poor sleep quality, because we know that sleep quality, independent of sleep quantity, is also associated with mortality risk. And the lower that your quality of sleep is, the higher your risk of death. People who have poor quality of sleep will typically try to sleep longer; they'll try to stay in bed longer to overcome that poor quality of sleep. It may be poor quality of sleep masquerading as long sleep that is associated with a higher risk of death, rather than the long sleep itself. But if we take a step back and think about society overall, I think modernity is constantly pushing us to, perhaps, work long hours and therefore neglect our sleep. But if we want to be around long enough to get the benefits and the fruits of all of that hard labor, we may want to think about starting to prioritize our sleep some more.