How many of you would interrupt a washing machine mid-cycle, asks Till Roenneberg as he begins his discussion at DLDw13. "Would you say stop. That must be enough?" Or would you expect your clothes to be very wet and probably dirty, he asks.
He links his example to sleep - an area we know very little about – but which also happens in cycles. Showing a graph mapping sleep across ages, the LMU professor demonstrates how we eat most when we are infants and young children, least during adulthood and a little more again in old age. "This graph is a little boring. We all know this." A more interesting picture is offered by his second graph, which shows the huge discrepancy between the amount people sleep on workdays and the hours they sleep on free days. On free days, we sleep like mad. "Too catch up." Next he shows a graph showing where in the world people get up when. Our sleep depends on the internal clock, which is set by light and darkness. Living in a country with an early dawn thus makes for more early risers.
Maria Furtwängler-Burda asks how to find out how much sleep is the right amount. Roenneberg says that is very difficult, because most of the sleep research done so far is actually sleep deprivation study, since most people are sleep deprived. As a test at home, Roenneberg says if a person takes four or five days where they allow themselves to wake up by themselves, they should have an indication of how much sleep they need.
Furtwängler-Burda points out that if she were to do that, she'd prob need 8.5 hours sleep, which she would never have time for on a typical day. R. says that because we do not get enough light, our internal clocks are late. In effect, we are living in two time zones, which Roenneberg calls "social jetlag". Which makes us fatter, more likely to develop diabetes, more prone to being a smoker, drink more coffee and consume more alcohol. Sleep is hence not just about quantity, but quality.
Our need for sleep, Roenneberg says, is genetic. There is not much we ca do to change it, but we can optimise the hours we give ourselves.