The premise: You’ve probably learned from experience how hard it is to function the next day after just a few hours of sleep. And though a sleepless night isn’t ideal, it’s not the worst thing in the world every once in a while. But Jane Ferrie, a senior research fellow at the University College London Medical School in Great Britain, wanted to know what would happen if subjects began to clock less sleep during a five-year period. “We already know that inadequate sleep is associated with poor performance and concentration; that there’s a relation between sleep and many health issues; and that change in sleep duration over a similar five-year period is associated with an increase in premature death,” Ferrie explains. But beginning to sleep for 10 hours a day isn’t the answer: Ferrie’s research also looked at subjects who added more hours to their slumber during the test period. Turns out, when it comes to REM, you need to make like Goldilocks and make a sleep schedule that’s juuust right. And stick to it. The set-up: Ferrie and a team of researchers studied more than 5,000 middle-aged men and women (ranging from 35 to 55 years of age) for five years. Their sleeping habits were tracked through questionnaires. Cognitive function was assessed using six standard tests that measured memory, reasoning, vocabulary, phonemic fluency, semantic fluency and global cognitive status.
Find us on Facebook! The results: During the five-year period, the participants who increased their sleeping baseline from 7 or 8 hours had lower scores at follow-up on five of six cognitive function tests. The only exception was the test of short-term verbal memory. The participants who decreased from 6, 7 or 8 hours per night were also linked to lower scores at follow-up. This time, at three of the six tests, including reasoning, vocabulary and global cognitive status. In both cases, the decline in mental function was equivalent to the level of cognitive decline you would normally expect to accompany an increase in age of four to seven years. The takeaway: Ferrie’s study focused on middle-aged people, so we asked her if she’d expect similar results with younger men: “I can't extrapolate the study and give you a definitive answer. However, many experiments on the effects of sleep deprivation have been carried out in healthy young men and they certainly show all the classic symptoms of lowered performance on tasks, attention and concentration deficits and adverse changes in endocrine function, so it is not unlikely.” She adds that younger people have more resilience but warns that chronic exposure to adverse sleep patterns will eventually take their toll at any age. “Hence the use of sleep deprivation as torture,” she points out. There’s a magical number when it comes to the optimal sleeping hours: “In our study, seven hours a night was associated with the highest cognitive function score in women, the men seemed to do equally well on anything between six and eight hours,” says Ferrie. “We don’t want people to worry about the findings from our study,” Ferrie says. “Rather, heed the message that people shouldn't be cavalier about sleep and should pay more attention to sleep hygiene.”