We tend to think of sleep as a time when our brains and bodies are dormant, but scientists spend a lot of their waking hours trying to understand the mysteries of this vital health activity. While you’re asleep, your muscles repair themselves, your brain clears away waste and stores new information, and hormones regulate everything from blood pressure to your hunger. Your body even gets rid of toxins that can build up in your brain and cause dementia. Without enough rest, you can have trouble learning, solving problems and concentrating, and a lack of sleep may also raise your risk for obesity, heart disease and depression.
It’s easy to see why getting a good night’s sleep is important, but many people don’t get enough. That’s especially true during times of stress, when our body’s natural systems kick into high gear to protect us and make it harder to fall asleep. It’s also challenging to get enough sleep when you have a busy schedule or chronic health issues. And even when you do get enough sleep, there are factors that can throw off your normal rhythms, like working the night shift or having an irregular routine.
Scientists know that your brain and body go through four stages during a sleep cycle, with each stage lasting about seven minutes. The first two are non-rapid eye movement (NREM) sleep and the last one is REM sleep, which is characterized by rapid eye movements and dreams. Scientists used to think that REM sleep was the most active part of sleep, but they now believe that NREM and slow-wave sleep are equally important.
The reason for this is that NREM and slow-wave sleep are thought to be critical for maintaining cognitive function. They’re also needed to prepare your brain for the next day and form new connections that help you learn, remember and concentrate. The brain also starts clearing cellular and protein debris, which helps prevent damage, as well as helping the immune system fight off infection.
One theory about why we need sleep is that it evolved to conserve energy, since finding food at night is more difficult. Another is that it’s important for regulating our mood, emotions and behavior. Some research also suggests that sleep can make you more resilient to stress and illness, by improving your immune response and ability to cope with difficult situations.
There’s also growing evidence that sleep may protect your physical and mental health, by protecting your brain from Alzheimer’s, lowering your risk of depression and increasing your memory capacity, and by reducing the chance of diabetes and heart disease. In addition, a growing body of research shows that sleep can improve your performance at work, school or on the playing field, as well as your creativity and ability to solve complex problems.