Some people have felt drawn to bed ever since they started making forts with pillows, and sleep at every opportunity.
For others, sleep gets in the way of fun or productivity. You may find yourself in a tug-of-war with sleep, staying up late as an act of generosity toward yourself as you unwind from the day, only to curse yourself hours later, when the alarm clock sounds.
We sleepers come in many varieties, but we all face the same reality when it comes to the way sleep affects the way we function and feel every day. Here's a distillation of what science has to say about the basics of slumber.
How much sleep is enough?
Well, “enough” means different things to different people. In decades past, it was thought that four to six hours was sufficient. Beyond that, you were getting “residual capacity” or, put another way, you were storing up your rest or, yet another way, you were lazy.
You can survive on that amount, but when people ask this question, they probably mean “how much do I need to feel good and function well?” Scientists often approach this question by restricting research subjects’ sleep until adverse consequences appear.
Bottom line: Seven to nine hours is the sweet spot.
What happens if I don’t get enough?
Insufficient sleep has been shown to lower the metabolic rate, and increase the production of certain hormones like grehlin (makes you hungry) and cortisol (the stress hormone that, for one thing, triggers the body to store fat). Together, these factors can lead to eating an extra 350-500 calories per day, and storing them as fat.
In adults, there is a strong association of restricted sleep with obesity, diabetes, hypertension, heart attack, stroke, and even arthritis. (In underslept children, the association with obesity is crystal clear.)
The sleepy also suffer from a range of cognitive impairments, including impaired memory, judgment, decision-making ability, creativity, and spatial learning, (rats negotiating a "water maze"; you navigating around a new city).
These effects can lead to an increased rate of car accidents, and lower GPA (by 0.5) in college students. Combined, the effects of the underslept body's inability to regulate metabolism, cognitive functioning, and hormone levels are just like those of aging.
Psychologically speaking, studies dating back to the 1970s have shown people with insufficient sleep to be more anxious and neurotic; modern studies show a link between fatigue and emotional instability, aggression, pessimism, and depression.
I’m special. I actually function fine on little sleep.
Most likely, you’re fooling yourself. It’s true that studies look at average sleep durations, and that there is variability among individuals, but not very much. Plus, you might well be impaired and not realize it.
For instance, one study found that after a period of extended sleep restriction (here, defined as fewer than eight hours), people rated themselves as only moderately sleepy, although they exhibited clear cognitive impairment.
But eventually, my body will just get used to it, and I’ll be fine, right?
Nope. The effects of inadequate sleep are cumulative, meaning that they continue accruing as long as you’re sleeping too little, and you can’t acclimate to them. The good news is that the effects are reversible . . . with sleep.
Fine, then. Should I just sleep straight through the night?
It depends on what you mean by “should.” Let’s start with our natural 24-hour circadian rhythm, which regulates our biological cycles. Scientists theorize that there is an evolutionary basis for this body clock (keeping you more alert when the risk of predators is high, for instance), so when people oppose it, problems ensue.
For instance, nocturnal people, like those who work the night shift, have higher rates of things like obesity, gastrointestinal disorders, and heart disease. (Our circadian rhythm isn't fixed, though, if you make some effort. In one study, people exposed to bright lights for four hours every evening were able to shift their body clock accordingly.)
Even for people with a typical schedule of daytime activity, the answer is a little sticky. With the exception of studies of long-term sleep deprivation, sleep studies generally assume the real-world scenario that most of us live with: regular cycles of light and dark, and a continuous chunk of waking hours. We go about our day, then go home and sleep, and then get up to do things again the next day.
So, you probably have little choice about how your sleep is structured. If that’s the case, then yes, sleep soundly through the night if you can.
However, a pragmatic sleeping pattern like that may not be the most natural one. In this TED talk, Jessa Gamble describes research subjects who volunteered to live underground for two weeks, with no environmental cues of passing time.
After a while, they fell into a pattern of four hours of sleep starting at 8:00 p.m., followed by two hours of “meditative quiet” in bed, followed by three or four more hours of sleep, from roughly 2:00 a.m. to sunrise (note the total of seven to eight hours).
They emerged from the study describing a quality of restedness that they had never experienced before. So, if your schedule accommodates it, you may want to see how an early bedtime works for you.
I’ve heard that we sleep in 90-minute cycles. Does this mean that I should sleep for multiples of 90 minutes?
This idea is popular in online forums, and is even the subject of a book about raising babies. It is true that we alternate between the deepest phase of sleep (REM) and the other phases of lighter sleep, on average, every 90 minutes or so. Intuitively, it would also make sense to start the day by emerging gently from a light sleep, instead of rudely from a deep slumber.
However, there appears to be no scientific support for the 90-minute cycle-timing approach, at least among adults. This might be because there are too many variables at play.
For one, there is a lot of variation in the length of sleep cycles, both between individuals and in the same individuals over the night. They can range from 70 to 120 minutes. Plus, how long our body “wants” to sleep on any given night is affected by where we happen to be in our overall circadian cycle when we drift off.
So, if you go to bed at the same time every night, and find yourself awakening in regular cycles, it couldn’t hurt to try to get up during a time when you’re typically sleeping lightly, but trying to impose precision on your sleep cycle probably won’t work.
There’s still no way I can get enough sleep at night. What about napping?
Napping can be helpful. One of the most interesting and frightening sources of information on this question is a report that emerged from a conference sponsored, in part, by the American Medical Association.
They were looking for ways to address the 98,000 deaths that occur each year in hospitals due to medical errors. (Ninety-eight thousand!)
They note, as mentioned above, that too little sleep can lead to poor judgment calls and confusion, and that overworked medical students can significantly reduce these effects by taking naps prior to a 24-hour shift and, during a 48-hour shift, by taking short naps every two to three hours.
There are two takeaways from this study:
- Taking naps can help you function better.
- Did I mention that suboptimal sleep also impairs motor skills? So, if your surgeon approaches you with baggy eyes and a scalpel, stand up immediately and demand that he or she take a nap!
Well, there you have it. Getting enough sleep is essential to our well-being, and we shortchange it at our own peril. For those of you who have trouble falling asleep sometimes, an article about insomnia is forthcoming.
If you’re having trouble falling asleep right now, however, I recommend following the research article links above which, I assure you, will have you sawing logs in no time.