Sleep, like diet and exercise, is an essential ingredient of good health.
No one needs to be told that sleep affects the brain, but now researchers are finding that it has direct effects on the rest of the body, too. Experiments have found that when you shortchange sleep, your immune system may nod off too and produce fewer antibodies.
Researchers at the University of Chicago have shown that when people sleep just four hours a night, various hormonal and metabolic systems fall into disarray. Their surmise: Chronic sleep loss might both hasten the onset and increase the severity of diabetes, high blood pressure, and obesity. The same group has also suggested that sleep deprivation from working long hours and bad living situations may explain why poor people tend to have many more health problems than those who are better off.
Good for the brain, too
Recent research is also clarifying how sleep affects memory and learning. If memories are created by strengthening the connections among networks of brain cells, sleep may be the brain’s way of tinkering with those connections — boosting some, dampening others.
Sleep may also serve an important editing function. Each waking moment is crammed with sensations, thoughts, and feelings. If your brain tried to store them all as memories, you might not remember a thing. Undoubtedly, you’re filtering a lot of this as it happens, but sleep seems to help afterward.
One theory of post-traumatic stress disorder is that it is caused by disordered sleep. After a bad experience has filled the brain during waking hours, inadequate sleep prevents the normal sifting and winnowing that moves these impressions into more integrated and less emotional memory systems. As a result, all the emotions and sensations of the traumatic experience keep coming back untamed.
At Harvard, researcher Richard Stickgold has used computer games like Tetris and Alpine Racer, along with simpler tests, to see how sleep affects memory and learning. His experiments have shown that people’s scores on certain types of memory tests improve without any additional practice as long as they sleep soundly and for at least six hours after first learning the task. He has also found that if you deprive people of the REM (rapid eye movement) part of their sleep the night after they learn a certain game, they show no improvement even after they sleep normally on subsequent nights. What’s more, the amount of improvement tracks closely with the amount of REM sleep in the final two hours of sleep.
It makes sense that REM sleep would be essential to some types of memory. Your brain is intensely busy during that phase, thus the rapid eye movement, and it’s when a lot of dreaming occurs. If you’re sleeping well, you go into REM sleep about every 90 minutes, so if you sleep about eight hours you get about four REM episodes. The first one lasts only a few minutes, but they get progressively longer, so the final episode may last about half an hour.
How much sleep do we need?
From diaries, letters, and literature, we know that a century ago most Americans got about nine hours of sleep a night. Now the average is about seven, and a third of us try to get by on six hours or less. Based on lab experiments that have allowed people to find their "natural" amount of sleep, researchers believe that most of us have our body clocks set so we require a little more than eight hours a night.
But there are a lot of impediments to getting those eight-plus hours. Midnight — it used to be in the middle of the night. Today it’s the time we turn off the television. The computer is a 24/7 enticement. Even the light bulb is trouble. The human species evolved with bright light in daytime and darkness at night. Our circadian rhythms adapted accordingly: Nighttime darkness triggered a surge of the hormone melatonin, leading to sleep, and dawn triggered awakening.
But for the past 100 years, we’ve illuminated our evenings with electric light. Sleep physiologists assumed that such evening light would not affect circadian rhythms because electric light is so much weaker than sunlight. But recent studies have shown that assumption to be wrong. Artificially lit evenings are disrupting our sleep and, although this is less clear, may be producing sleep disorders in some of us.
