Sleep is one of the strangest things we do each day. The average adult will spend 36 percent of his or her life asleep. For one-third of our time on earth, we transition from the vibrant, thoughtful, active organisms we are during the day and power down into a quiet state of hibernation.
The first purpose of sleep is restoration. Every day, your brain accumulates metabolic waste as it goes about its normal neural activities. While this is completely normal, too much accumulation of these waste products has been linked to neurological disorders such as Alzheimer’s disease.
During sleep, brain cells actually shrink by 60%, allowing the brain’s waste-removal system—called the glymphatic system—to essentially “take out the trash” more easily. The result? Your brain is restored during sleep, and you wake up refreshed and with a clear mind.
Sleep is crucial for memory consolidation, which is the process that maintains and strengthens your long-term memories.
when you sleep 5.5 hours per night instead of 8.5 hours per night, a lower proportion of the energy you burn comes from fat, while more comes from carbohydrate and protein. This can predispose you to fat gain and muscle loss.
The four-hour group performed worst, but the six-hour group didn’t fare much better.
Let me repeat that: if you get 6 hours of sleep per night for two weeks straight, your mental and physical performance declines to the same level as if you had stayed awake for 48 hours straight.
The irony of it all is that many of us are suffering from sleep deprivation so that we can work more, but the drop in performance ruins any potential benefits of working additional hours.
“Unless you’re doing work that doesn’t require much thought, you are trading time awake at the expense of performance.”
Generally speaking, experts agree that 95 percent of adults need to sleep 7 to 9 hours each night to function optimally. Most adults should be aiming for eight hours per night. Children, teenagers, and older adults typically need even more.
Working hard in the gym, at school, or at the office allows you to produce something of value. But even positive outputs are still outputs and they drain your energy accordingly.
Recovery is not negotiable. You can either make time to rest and rejuvenate now or make time to be sick and injured later.
During slow wave sleep the body relaxes, breathing becomes more regular, blood pressure falls, and the brain becomes less responsive to external stimuli, which makes it more difficult to wake up. This phase is critical for renewal and repair of the body. During slow wave sleep, the pituitary gland releases growth hormone, which stimulates tissue growth and muscle repair. Researchers also believe that the body’s immune system is repaired during this stage. Slow wave sleep is particularly critical if you’re an athlete. You’ll often hear about professional athletes like Roger Federer or LeBron James sleeping 11 or 12 hours per night.
REM sleep is to the mind what slow wave sleep is to the body. The brain is relatively quiet during most sleep phases, but during REM your brain comes to life. REM sleep is when your brain dreams and re-organizes information. During this phase your brain clears out irrelevant information, boosts your memory by connecting the experiences of the last 24 hours to your previous experiences, and facilitates learning and neural growth. Your body temperature rises, your blood pressure increases, and your heart rate speeds up. Despite all of this activity, your body hardly moves. Typically, the REM phase occurs in short bursts about 3 to 5 times per night.
To summarize: slow wave sleep helps you recover physically while REM sleep helps you recover mentally. The amount of time you spend in these phases tends to decrease with age, which means the quality of your sleep and your body’s ability to recover also decrease with age.
The circadian rhythm is a biological cycle of different processes that happen over a time span of about 24 hours.
The circadian rhythm is impacted by three main factors: light, time, and melatonin.
Light is probably the most significant pace setter of the circadian rhythm. Staring into a bright light for 30 minutes or so can often reset your circadian rhythm regardless of what time of day it is. More commonly, the rising of the sun and light striking your eyes triggers the transition to a new cycle.
This is the hormone that causes drowsiness and controls body temperature. Melatonin is produced in a predictable daily rhythm, increasing after dark and decreasing before dawn. Researchers believe that the melatonin production cycle helps keep the sleep-wake cycle on track.
Process 1 is sleep pressure. Basically, sleep pressure mounts from the moment you wake up, to the time when you go to sleep. While you’re sleeping, pressure decreases. If you get a full night of sleep, you start the next day with low sleep pressure.
Process 2 is wake drive, which counteracts sleep pressure and is controlled by a 24-hour rhythm that repeats in a wave-pattern.
For millions of years, humans and our ancestors have evolved to sleep at night (when it is dark) and wake during the day (when it is light). However, in the modern world, we work inside all day, often in areas that are darker than the outside world. And then, at night, we look at bright screens and televisions. Low light during the day, more light at night: It’s the opposite of naturally occurring cycles and it seems quite likely that it could mess up your wake rhythm and circadian rhythm.
“The time of night when you sleep makes a significant difference in terms of the structure and quality of your sleep,”
So how early do you need to be to bed to get enough of each type of sleep? Walker says there’s a window of several hours, about 8 p.m. to midnight.
When choosing your bedtime, try not to fight your physiology. The best bedtime will differ a little bit for everyone, but it’s crucial that you pay close attention to your internal clock and what your body is telling you. As long as you’re getting the recommended 8 hours of sleep, just focus on finding the time that works best for you.
Use relaxation techniques. Researchers believe that at least 50 percent of insomnia cases are emotion or stress related. Find outlets to reduce your stress and you’ll often find that better sleep comes as a result. Proven methods include daily journaling, deep breathing exercises, meditation, exercise, and keeping a gratitude journal (write down something you are thankful for each day).
From a practical application standpoint, timing is perhaps the most important of the 3 levers of sleep. The intensity of your sleep is managed automatically by your body. The duration of your sleep is largely dependent on when you get into bed (assuming you wake up around the same time each morning). And that means getting to bed at an earlier, more consistent time is critical for improving the quality and duration of your sleep.
Fit middle-aged adults sleep significantly better than their overweight peers. One caveat: avoid exercising two to three hours before bedtime as the mental and physical stimulation can leave your nervous system feeling wired and make it difficult to calm down at night.
Most people sleep best in a cool room. The ideal range is usually between 65 to 70 degrees Fahrenheit (18 to 21 degrees Celsius).
A quiet space is key for good sleep. If peace and quiet is hard to come by, try controlling the bedroom noise by creating “white noise” with a fan.