A ciência do sono em inglês: aula de conversação em 3 níveis (com Matthew Walker)

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Sleep is very important for the body and the brain. When we sleep, the body goes through different stages. There are two main types: NREM sleep and REM sleep. NREM sleep is deep and slow. REM sleep is lighter, the brain is very active and the eyes move fast.

Humans and chimpanzees

Humans and chimpanzees sleep in different ways. A chimpanzee sleeps about 9 or 10 hours a day. A human sleeps about 7 or 8 hours. Chimpanzees sleep in trees, where they are safe from predators. So they can sleep longer. But a tree is not a comfortable bed: a chimpanzee can fall, and this can wake it up. The place where an animal sleeps changes how long and how deep it sleeps.

Not everybody sleeps the same way

People in the same group have different sleep patterns. Some people are "morning people": they feel good early in the day. Other people are "night owls": they work better at night. This is good for the group. When some people are awake, they can see danger. Scientists call this the "sentinel hypothesis". Genetics, age, lifestyle and health also change how we sleep.

Two clocks

Two things control our sleep. The first is the circadian rhythm. It is the body's internal clock. It follows a 24-hour cycle and it uses light and temperature. It makes us feel awake in the day and sleepy at night. The second is the homeostatic process. The longer we are awake, the more we need to sleep.

A short nap in the middle of the day, 30 to 60 minutes, can give us more energy and a better mood. It is also important to sleep enough hours and to wake up at the same time every day. Look at the chart below to understand the sleep cycles.

Conclusion

Sleep is complex, and it affects the body, the mind and the emotions. When we understand what controls our sleep, we can change small habits and sleep better.

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Good sleep depends on five things: time, light, temperature, caffeine and habits.

Go to bed at the same time every day. Wake up at the same time every day, also on weekends. In the morning, go outside and get daylight for five to fifteen minutes. A cold shower in the morning helps you wake up.

If you are tired, take a short nap early in the afternoon. Don't drink coffee after 2 pm. Don't drink alcohol before bed. Don't eat a big dinner late at night.

At night, use only weak, warm light. Keep the bedroom dark and cool, around 19 °C. A warm shower before bed helps you fall asleep.

If you are in bed for twenty minutes and you can't sleep, get up. Come back only when you feel sleepy. A sleep mask, dark curtains and a constant soft noise protect your sleep.

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Sleep is an investment. When you sleep well, your brain, your mood, your immune system, your metabolism and your heart all get better results. The results grow night after night.

Deep sleep (NREM) saves your memories. REM sleep cleans your emotions (Walker, 2017). After one night without sleep, the emotional part of the brain reacts too much, and the rational part loses control (Yoo, 2007). People who sleep little get sick more often when they meet a cold virus (Prather, 2015). Little sleep also increases inflammation in the body (Irwin, 2006).

Sleep also changes how we eat. When we sleep less, the hormones of hunger change, we feel hungrier, and we gain weight (Taheri, 2004). Less sleep also means higher blood pressure (Czeisler, 1999). In big studies, people who sleep little have more strokes, more heart attacks and die earlier (Cappuccio, 2010).

The message is the same in many countries and many laboratories: sleeping less damages health in ways we can measure and we can prevent.

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Many busy people sleep six hours, not eight. The idea is simple: two hours less in bed means two more hours for work. That is fourteen hours a week. It sounds like a good trade.

But scientists tested this idea. In one study, people slept six hours a night for two weeks (Van Dongen, 2003). At the end, their brains worked as badly as the brains of people who did not sleep for one or two nights. And the strange part: they did not feel very tired. They thought they were fine.

Other studies show the same thing. After seventeen to nineteen hours awake, people perform like someone who drank alcohol (Williamson, 2000). Companies pay for this too. In the United States, tired workers cost more than a million working days every year (RAND, 2016).

Some people really can sleep less without problems. They have a rare gene (He, 2009). But they are very, very rare. Most people who say "I only need five hours" are not in this group.

So, is the trade good? You get more hours, but each hour is worse. And the worst part is that you can't see it.