Sleep sounds simple. Everyone can sleep. From babies to dogs to computers. But it is not so simple. I recently read a book by Matthew Walker called “Why we sleep” and I learnt all about how complicated sleep is. It turns out that sleep is not just about “passing out”. It also turns out that most of us don’t sleep properly. And the implications of not sleeping well are staggering.
The author, Matthew Walker, is a Professor of neuroscience and psychology at the University of California, Berkeley and describes himself as a “sleep scientist”. He is a leading researcher in the field and parts of the book reads like a conversation between him and his critics in academia. Those bits get a bit boring, but there is a lot I learnt from this book that I want to share here.
Is Sleep Silly?
I had never really thought much about sleep. But once you start thinking about it, you wonder why we waste one third of our lives sleeping. Nature had created life so that living beings can eat, grow and procreate. When we are sleeping, we can do none of those things. Moreover, sleeping is actually dangerous, since we are vulnerable to predators when asleep. So why haven’t we evolved so that we don’t need sleep? Clearly nature thinks that sleeping is critical to our well being.
Science has figured out that sleep is as important as diet and exercise. In fact, Dr Walker is vehement about this. He says, “The physical and mental impairments caused by one night of bad sleep dwarf those caused by an equivalent absence of food or exercise. It is difficult to imagine any other state—natural or medically manipulated—that affords a more powerful redressing of physical and mental health at every level of analysis. Based on a rich, new scientific understanding of sleep, we no longer have to ask what sleep is good for. Instead, we are now forced to wonder whether there are any biological functions that do not benefit by a good night’s sleep.”
Sleep makes you creative
OK, so sleep is needed for rest and recovery. Ho, hum. Didn’t we already know that? Well, it turns out that we are now learning how sleep is even more important for our mental processes. For our learning and creativity. This bit was new and interesting for me.
Think of your brain as containing a hard disk and a pen-drive (one of those small devices, also called USB stick, we use to store and transfer digital files). While we are awake, all our learning is adding data to this pen-drive. At some point the pen-drive gets full and we can no longer absorb more information. That’s when we find ourselves reading the same passage over and over again, without learning anything new. Time to go to sleep, because when you sleep, the data from your pen-drive will get written into the hard disk, and the pen-drive is cleaned and ready for a new day of learning.
Not only that, while you sleep, the new data in the hard disk, connects with all the existing data that is already there and new connections get formed. This is how you get your creative ideas. This is why you get some of your best ideas when you wake up from a good sleep. All the work you did before you slept has been processed and cross referenced with everything you knew before. And Eureka! This felt like a really compelling reason to sleep properly.
When is it time to sleep?
But what makes us feel sleepy?
Turns out that there are two independent processes happening in your brain that lead to sleep. One is called the circadian rhythm. This is something all living creatures have. It is like a clock that is ticking away inside your head and tells you when to wake up and when to sleep. The rhythm has a roughly 24 hour cycle and it works even if you can’t see the sun and don’t have a watch. Your body just knows that it is morning or night because of this circadian rhythm.
Different people have different rhythms and the same person has different rhythms at different stages in life. So a baby’s circadian rhythm causes it to sleep practically the whole day. While a teenager’s rhythm kicks in later in the night and continues till late in the morning. That is why teenagers have problems waking up in the morning. That same teenager will be fine once they become an adult.
Also some people are morning types and some night types. It seems that 40% of us are morning types while 30% are night types. The rest are hard to classify.
There is another process at work, which creates something called the sleep pressure. When you are awake, a chemical, called adenosine, is being deposited on the neurones in your brain. As the amount of adenosine increases, your sleep pressure increases. This keeps building up and up until you go to sleep. After you have slept for eight hours, all the adenosine in your brain has been washed away and your brain is ready to work again.
The circadian rhythm and the sleep pressure are independent processes and are not always in sync. However, your sleep is best at times when the two cycles coincide. In other words, it is best to sleep when your circadian rhythm tells you it is sleep time and when the sleep pressure is maximum.
Jet lag occurs when your circadian rhythm thinks it is day but your sleep pressure is high and your brain feels it needs to sleep. Or your rhythm thinks it is night, but your sleep pressure hasn’t built up yet. Both lead to problems. Everyone who has travelled by air into other time zones has experienced this. But we subject our bodies to the same stresses when we stay up late or, worse, don’t sleep all night. Our sleep pressure keeps going up and up while our circadian rhythm thinks it is time to wake up.
The book documents a lot of harmful effects of these states. What really surprised me was that science has discovered that you can never make up for lost sleep. If you don’t sleep for one night, you create damage to your body and to your mind that can never be fully repaired. Quite a sobering thought, that.
Coffee and other harmful drugs
I love coffee, but Dr Walker says it is the most addictive substance that we willingly consume. Moreover, it messes up our sleep system.
The caffeine in the coffee (and in tea, for that matter) rushes into your brain and occupies the spots meant for the adenosine. So your brain is tricked into not feeling the sleep pressure. However, caffeine lasts in our body for a few hours and when it gets washed out, the adenosine hits us like a tidal wave. So coffee does perk you up when you start to feel sleepy, but then you feel really sleepy when the effect wears off.
Coffee affects the sleep pressure, but has no effect on the circadian rhythm and so it can send your sleep cycle out of whack. It leads to incomplete or bad quality sleep and that leads to many problems.
Types of sleep
Did you know that there are various types of sleep? And that you need to have balanced portfolio of each kind? Quite like having a balanced meal.
It turns out that human beings have a rhythm in our sleep. We sleep in 90 minute cycles. Each cycle consists of light sleep, deep sleep and REM sleep (I am simplifying a bit here). When you go to sleep, the early cycles have more of the deep sleep and less of the REM sleep. The later cycles (especially after you have been sleeping for six hours) have more of the REM sleep.
The difference lies in the extent of brain activity and the relaxation of your physical body. In deep sleep, your brain is quite still, while in REM sleep your brain is quite active - almost as much as when you are awake. During REM sleep your body is totally immobile and if you are woken up suddenly during it, you may have difficulty in walking. You may stumble if you try to walk.
Deep sleep and REM sleep both have different functions. Deep sleep helps to clear that pen drive and also repair your physical body. The REM sleep is needed to connect the new data in your brain with what already exists and is critical in knowledge creation and creativity.
How to sleep well
This has already become a long post, so let me conclude this by providing Dr Walker’s 12 tips for sleeping well. Here we go:
1. Stick to a sleep schedule.
2. Exercise is great, but not too late in the day.
3. Avoid caffeine and nicotine.
4. Avoid alcoholic drinks before bed.
5. Avoid large meals and beverages late at night.
6. If possible, avoid medicines that delay or disrupt your sleep.
7. Don’t take naps after 3 p.m.
8. Relax before bed.
9. Take a hot bath before bed.
10. Dark bedroom, cool bedroom, gadget-free bedroom.
11. Have the right sunlight exposure.
12. Don’t lie in bed awake.
There is a lot of science behind each of these tips. Read the book if you want to know more.
I came away from this book quite shaken up. Dr Walker insists that we all need to sleep between 7 to 8 hours a day. We also need a short nap in the afternoon in addition to the sleep at night. Most of us don’t have enough quantity of sleep. Moreover, even the sleep that we have is not good quality. I have been monitoring my sleep over the past few days using my smartwatch, and I am amazed at how my REM sleep is way below what it needs to be.
No wonder I don’t get bright ideas anymore.