Saturday science subject: Sleep debt

— 2:30 PM on October 18, 2008

Do westerners get enough shut-eye these days, or have our hectic lifestyles given us a massive collective sleep debt? Although some claim the latter, Jim Horne from the University of Loughborough in the UK thinks that's rubbish. Here's what he writes in the New Scientist:

Over the past 40 years, there have been several large studies of how much sleep people actually get, and the findings have consistently shown that healthy adults sleep 7 to 7½ hours a night.

The well-known "fact" that people used to sleep around 9 hours a night is a myth. The figure originates from a 1913 study by researchers at Stanford University in California, which did find that average daily sleep was 9 hours - though this applied to children aged 8 to 17, not adults. Even today, children continue to average this amount.

If we spend more time snoozing on weekends and holidays, though, doesn't that mean we're not getting enough sleep the rest of the week? That might be the case for some folks, but Horne has another explanation:

However, just because we can easily sleep beyond our usual daily norm - the Saturday morning lie-in, the Sunday afternoon snooze - it doesn't necessarily follow that we really need the extra sleep. Why shouldn't we be able to sleep to excess, for indulgence? After all, we enthusiastically eat and drink well beyond our biological needs. Why shouldn't it be the same with sleep?

Most mammals will sleep for longer than normal if overfed, caged or bored. The three-toed sloth is a good example. Sloths kept in zoos sleep around 16 hours a day - yet in their natural, wild state they sleep less than 10. . . . This is seen in domestic animals too. Sheep in pens, horses in stables and cows in barns sleep much more than when in open fields, and pet cats sleep extensively compared with feral cats.

Actually, Horne goes as far as to claim we sleep better than ever nowadays. A worker in the mid-19th century "toiled for 14 hours a day, six days a week, then went home to an impoverished, cold, damp, noisy house and shared a bed not only with the rest of the family but with bedbugs and fleas," he points out.

In a recent study, Horne says his team at the University of Loughborough's Sleep Research Centre asked 11,000 subjects how much they slept each night—and how much sleep they felt they needed. Half of the subjects said they had a sleep shortfall (averaging 25 minutes per night) and 20% of all subjects said they were excessively sleepy during the day. However, Horne says the subjects with sleep shortfalls were no sleepier than others during the day, and when asked what they'd do with an extra hour each day, only a "handful" said they'd use it to sleep.

In the end, Horne concludes, "Propagating the myth of a chronically sleep-deprived society is not only intellectually lazy, but further adds to the anxieties of people who believe they are not getting enough, creating unfounded health concerns and a greater demand for sleeping pills."

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