The science and significance of sleep

“Sleep is the single most effective thing we can do to reset our brain and body health each day.”

– Why We Sleep, by Dr. Matthew Walker. 

Sleep affects our memory, immune system, weight regulation and mental health. Not getting enough sleep doubles your risk of cancer. It makes you more likely to develop Alzheimer’s disease. It affects your blood sugar and your likelihood of heart failure. It also makes you want to eat more. Clearly, sleep is important!

Walker’s book helped me understand what actually happens when we sleep. Sleep is largely regulated by two factors: circadian rhythm and sleep drive. A circadian rhythm is a 24-hour cycle with a peak – when you feel awake and alert – followed by a trough – when you feel tired. Sleep drive depends on a chemical called adenosine which creates “sleep pressure.” The level of adenosine drops when you fall asleep and starts to rise again when you wake. You find it easiest to fall asleep when adenosine levels are high and your circadian rhythm is at a low point. 

Each night, we experience two main types of sleep: rapid eye movement (REM) sleep and NREM (non-rapid eye movement) sleep. Both kinds have incredible benefits. We start out with mostly deep-level NREM sleep. During this stage, the brain sorts and solidifies memories, pruning brain connections and clearing toxins from the brain. This kind of sleep is critical for learning information, which is why a professor in college told my class that “An hour of sleep before midnight is worth two hours after.” During later sleep cycles, we experience the majority of our REM sleep. During this stage, brain connections are strengthened and emotions are sorted and reset. If you go to bed very late, you will lose out on deep NREM sleep. If you get up too early, you can lose 60 to 90 percent of REM sleep. 

Mental health & technology  

Sleep and mental health are intimately connected. “Psychiatry has long been aware of the coincidence between sleep disturbance and mental illness,” Walker writes. “There is no major psychiatric condition in which sleep is normal.” Psychiatrists have speculated that mental disorders result in sleep disruption. But it goes the other way as well; sleep disruption can contribute to mental disorders. Knowing that, it stands to reason that establishing healthy sleep patterns could help prevent or treat mental health conditions. 

Sleep disruption has been linked to suicidal thoughts, aggression, behavioural problems, and addiction. Dr. Walker describes a study from the 1960s – which would not be allowed today – in which researchers deprived healthy young adults of REM sleep. The subjects were allowed to sleep, but every time a test individual entered REM sleep, they were awakened. The study was done for a week. After just three days, “participants were expressing signs of psychosis. They became anxious, moody, and started to hallucinate. They were hearing things and seeing things that were not real. They also became paranoid…..Describe these symptoms to a psychiatrist without informing them of the REM-deprived sleep context, and the clinician will give clear diagnoses of depression, anxiety disorders, and schizophrenia.”  

REM sleep is critical for regulating emotions. Our brains produce a hormone and neurotransmitter called noradrenaline. Dr. Walker says, “REM sleep is the only time during the twenty-four-hour period when your brain is completely devoid of [the] anxiety-triggering molecule [noradrenaline].” During this time of REM sleep, your brain can relax. As your mind sorts through recent experiences, it can do so in a safe environment during which emotions can be processed and softened; later, you’ll be able to remember the experience without the negative or traumatic emotions you might have felt when it happened. 

We live in a broken world, and many of us face disordered sleep for other reasons. Parents of babies and young children, who wake frequently in the night, experience the toll of disrupted sleep. Women approaching menopause and elderly people often experience insomnia or wake too early in the morning to feel fully rested. 

While some impediments to sleep are beyond our control, others result from habits that interrupt sleep. For example, caffeine and other stimulants block our bodies’ ability to recognize adenosine, which is supposed to make us aware of our need for sleep. Use of devices like smartphones, tablets and computers near bedtime, or leaving them in your bedroom, can also negatively impact sleep. The light from these devices is the main problem. Blue light, like that emitted from phones and tablets, hits the retina and signals “sunlight” to your brain, suppressing production of a hormone called melatonin. Melatonin signals to your body that it is time to sleep, so a delay in the release of this hormone can make it difficult to fall asleep. Because phones and tablets are backlit (with the light coming from behind the screen), the light from them shines directly into your eyes, rather than just reflecting off what you are looking at; this means more of the blue light enters your eyes. In an experiment described in Why We Sleep, subjects were asked to read before bed. Some subjects read a paper book and others read a book on an iPad (which is backlit with blue light). The people who read on the iPad felt sleepier and less rested the next day. They had a more difficult time falling asleep, because their rise in melatonin levels was delayed by up to three hours – and was similarly delayed for days afterward. People who read on an iPad also experienced less REM sleep. (Note: most e-readers are not backlit and thus are less problematic when it comes to disrupting sleep, but it is still a good idea to turn down the screen brightness in the evening.)

Keeping a phone or device in your bedroom also negatively impacts sleep. The blue light from screens is one reason. Also, pings and other notifications can distract you and make you want to check your device. A better option is to buy an alarm clock and leave your phone in a different room. 

Sleep as a gift

I think faith helps us answer the deeper question of why we sleep: we sleep because God has gifted us with this marvellous phenomenon. How can we receive that gift in a way that honours him? 

One important thing about a gift is that it needs to be actively received. When you give someone a gift, it is up to that person to open and use it. The saying, “In receiving a gift you honour the giver” gets at this. If sleep is a gift from God, how can we receive that gift in a way that honours him? 

First, I think receiving this gift properly leads to a change in posture. Rather than grumbling over the need to sleep, or feeling guilt because we “should” get to bed earlier, or denying our need for sleep, we can accept sleep with gratitude. We get to rest our bodies and minds each night because of the generosity of a good God! 

Second, recognizing sleep as a gift helps us realise our limits. We cannot make ourselves sleep. What we can do is make room for sleep to do its work. This ought to make us humble. 

Third, God’s gift of sleep invites us to rest in him. Psalm 121:4 says that God “who watches over Israel will neither slumber nor sleep.” God does not sleep, so that we can. We acknowledge our dependence on God and trust him to keep and protect us through the night.  

Establishing good habits can be a way to steward the gifts God has given us and to extend the fruits of the Spirit. For centuries, Christians have used spiritual disciplines – intentional habits – to open themselves to God. In our modern world, setting limits on our technology use is a type of spiritual discipline. Prioritising sleep is a way to steward the gift of sleep. Building habits to support mental health demonstrates stewardship of our minds and bodies. All of these make us healthier, happier, more whole people.