Why You Need to Sleep

Sleep is often considered to be a time when your body shuts down and takes a break. But scientists have found that, as you rest, some parts of your brain and body are surprisingly active. And that a good night’s sleep supports a variety of essential functions, including mental and physical health.

For example, during REM sleep, the brain clears away waste that builds up during waking hours. And it converts short-term memories into long-term ones to help you learn. It also regulates hormones that control your appetite and stress levels, and it helps you maintain a healthy weight. And it plays a critical role in your immune system’s ability to fight disease and infection.

Insufficient sleep can also affect how well you think and react, especially under pressure or in dangerous situations. In fact, getting less than a recommended amount of sleep increases your risk of car accidents and other serious problems. Sleep deficiency can also raise your risk for heart disease, high blood pressure, diabetes, depression, and obesity, and can lead to poorer work performance.

So how much sleep do you need to feel and function your best? There’s no one-size-fits-all answer, but most experts agree that adults need between 7 and 8 hours a night. Teenagers may need a little more, and older people can usually get by with a bit less.

The reason you need to sleep is that your body and brain run on a cycle of being awake and asleep each day, called the circadian rhythm. This cycle is matched to Earth’s 24-hour day and night, and helps you stay alert during the day and get enough rest at night.

When you sleep, your heart rate slows, and muscles relax. Eye movements stop, and your brain-wave activity decreases, with occasional bursts of activity called “sleep spindles” that can aid memory processing. You cycle through non-REM and REM sleep several times during the night, with REM periods getting longer and deeper as the night goes on.

During REM, your brain becomes very active, and you have vivid dreams. The amygdala, an almond-shaped region involved in emotional responses, becomes particularly active. This might explain why you’re more likely to remember emotional events from your life when you’re dreaming, than when you aren’t.

The other major part of your sleep cycle is non-REM, or N2. During this stage, your breathing and heart rate slow further, and your body temperature drops. Your muscles become more relaxed, and you spend most of your sleeping time in a deep phase of N2 known as slow-wave sleep (SWS), which makes up around 45% of the total time spent sleeping. This is when your body does most of its healing and repair, and when it releases growth hormone to support tissue growth and bone development. It’s also when your body produces antibodies to fight disease and infections. You can’t see these processes, but they’re vitally important to your overall health and well-being.