Should I Be Sleeping Less at Night and Taking More Naps?
I read that the human sleep cycles last 90 minutes, so people are more rested if they sleep in increments of 90 minutes—7.5 hours, for example, is better than eight. Is that true? And what about sleeping for 4.5 hours at night, then supplementing with a few 90-minute naps? Is that the same as sleeping for 7.5 hours?
The short answer: No and no.
The long answer: People have long been looking for ways to squeeze more productivity out of every 24-hour cycle, particularly if they’re trying to wedge training into an already stuffed schedule. So it makes sense to experiment with sleep to get a few hours back.
In a 1943 Time agazine article, for example, American Rennaissance man Buckminster Fuller famously touted his “Dymaxion” sleep system, in which he slept for 30 minutes every six hours, as the cure for the “bad habit” of sleeping. More recently, bloggers and magazine writers (including Outside’s Tim Zimmerman) have documented their self-experimentation in polyphasic sleep (taking multiple naps), as opposed to monophasic sleep (sleeping in one big chunk) with less than stellar results. (“After two days I was a walking ghoul, barely able to make a pot of coffee,” Zimmerman wrote of his attempt to sleep for 15 minutes every four hours).
In addition to extreme endurance athletes, who may race for days at a time (see: Race Across America), the U.S. Army has been particularly interested in finding a sleep schedule that will allow soldiers on duty to sleep less without sacrificing their physical and cognitive abilities. Recently, however, it seems like experiments have been moving away from finding a suitable polyphasic sleep pattern to developing drugs that will enhance performance even while soldiers are exhausted.
Why? Because humans really do need sleep in one chunk, preferably a seven- to nine-hour chunk, says Dr. Jamie Zeitzer, a psychiatry and behavorial science professor at Stanford University, and a member of the school’s Circadian Research Laboratory.
To answer your first question, Zeitzer says the 90-minute cycle is an average. Your cycle may be shorter or longer, making it unnecessary for you to sleep in 90-minute increments. (There are currently gizmos on the market that can help you determine your sleep cycle so you wake up rested at the end of your cycle, including the Sleep Zeo and the Sleep Cycle iPhone app.)
To answer your second question: “The impression I get from the research that’s been done is that napping is not the same as nighttime sleep,” Zeitzer says. “You’ve got different sequences that occur during napping than those that occur during nighttime sleep.” So napping should be a supplement to nighttime sleep if you’re not getting enough, not a substitute. How do you know if you’re not getting enough? Zeitzer’s rule of thumb: “If you sleep in on the weekends, you’re not getting enough sleep during the week.”
And sleep deprivation can have dire health consequences. “There’s a lot of evidence that disrupted sleep contributes to weakening the immune system,” Zeitzer says. “You get sick more readily, the memory doesn’t work as well—nothing works quite right.” Researchers have even been examining a link between lack of sleep and the development and progression of cancer.
THE BOTTOM LINE: You don’t have to sleep in 90-minute increments, and researchers currently believe that napping doesn’t provide the same brain and body restoration that nighttime sleep does. Unless you’re gunning for the Race Across America record or preparing for battle, it’s best to nix other activities that are sapping your daily productivity.