Sleep experts recommend that healthy adults usually have seven to nine hours of sleep each night (ten hours for children and nine for teenagers). However, recent research into sleeping patterns shows that seven, not eight hours is the optimal sleep duration for adults.
More or less than this amount is associated with poorer performance at work and many other problems.
Professor Shawn Youngstedt from Arizona State University says: "The lowest rate of mortality and disease is linked to seven hours of sleep per night. Eight hours or more can be dangerous." This opinion is shared by Professor Daniel Kripke of the University of California, whose extensive research into people who sleep 6.5 to 7.4 hours per night recorded a significantly higher survival rate than others.
A neuroscientific study into sleep last year also showed that cognitive performance increases as the amount of sleep increases. This, however, peaks at seven hours, whereupon performance decreases. "Therefore longer sleep does not provide additional benefits," concludes lead researcher Murali Doraiswamy.
Despite extensive scientific evidence about the dangers of 'oversleeping’, some experts remain skeptical. For example, Timothy Morgenthaler from the American Academy of Sleep Medicine says: "The problem with these studies is that they create a lot of associative connections, but not necessarily causal connections."
Morgenthaler therefore recommends a more traditional regimen of seven or eight hours a night. He also stresses that individual optimal sleep schedules may vary markedly due to genetic and cultural differences.
Three days to a week are needed in order to determine your own optimal required sleep time (ideally when on vacation). During this period you should avoid excessive caffeine and alcohol consumption and refrain from using an alarm. Just go to bed when you are tired and avoid electronic gadgets several hours before bedtime.
Keep a record of your sleep times during this period. If you feel fresh and awake during the day, then you have determined your optimal number of hours of sleep - and according to the latest sleep studies (including this one where volunteers lived in 'prehistoric' conditions for over two months) you're more likely to come closer to seven hours, rather than eight.