We spend most of our time thinking about the usual things--our family, our friends, our work, our possessions, our wealth, our training and nutrition, our hobbies. But these only occupy us in the two-thirds of life during which we are awake. What about the other third of our life? Do we devote a third of our energy and attention to it? In this two-part post I will discuss the what, why, when, where and how of sleep.
WHAT IS SLEEP?
Sleep is actually quite difficult to define. Most of the time, it is referred to as a naturally recurring and cyclical state of mind and body--or something similar to that. The similarities of definition are mirrored by the similarities of features often cited as part of sleep. They include:
- An altered consciousness.
- Inhibited sensory activity.
- Reduced activity of all voluntary muscles.
- Decreased reaction to external stimuli.
The difficulty in defining it isn't of too much importance, though. We all know what we're talking about when we talk about sleep. Which brings me to the next question...
WHY DOES IT MATTER?
Answer: because its presence (or absence) has a massive impact on us. For example:
- Sleep affects the nervous system: Sleep deprivation impairs nervous system function. Without enough sleep, muscle fiber recruitment is slower and its efficiency is harmed, reaction times are diminished, and fine and gross motor control becomes less precise.
- Sleep affects the muscular and skeletal system: sleep is an anabolic state--during it, our muscles, connective tissue and bones recover and grow. The stresses they suffer do not turn to strength without consistent and plentiful periods of sleep.
- Sleep affects the endocrine system: the endocrine system is a chemical messenger system responsible for distributing hormones around the body and ensuring the optimal function of different organs and systems. When it is disrupted by lack of good quality sleep, it malfunctions. Studies have shown chronic sleep deprivation can contribute to an increased risk of Type 2 diabetes, obesity and a host of other metabolic disorders.
- Sleep affects the digestive system: contrary to other systems, sleep is a time of rest for the digestive system, its downtime. It gives the parts of the body involved in digestion a chance to reset, recover their energy, and replace important hormones and enzymes. Deprived of sleep, the digestive system becomes overtaxed and functions sub-optimally.
- Sleep affects the functions of the brain: the main controller of the mind and body is, as you'd expect, pretty reliant on sleep. Without it, creativity is lessened, concentration is shorter and less intense, the chances of anxiety and depression are increased, and retention of ideas and experiences drops dramatically. We become less social, less amenable to doing new things and less inclined to learn. Conversely, when we get all the sleep we need, we have more energy and operate in a better mood. We are more creative, more engaging and capable of being deeply immersed in experiences, we are better able to solve problems and ask questions, and we are less likely to fall prey to acute or chronic anxiety and depression.
- Sleep affects performance: those who perform consistently to the best of their ability get enough sleep. High performance requires you to be in a prime physical and psychological state--sleep is a key component of that.
See? Sleep really, really matters. Yet, it is one of the first things we sacrifice. Got a deadline at work? Miss an hour of sleep. Have an important competition in a few weeks? If you get up a little earlier you can train more and do better...
In our culture of workaholics and productivity worship, sleep isn't yet seen as optional, but it is regarded as a low priority. But what we forget is that just one less hour of sleep can make every hour of the following day less effective, less efficient, less productive. For example, is it better to miss an hour of sleep but train for two hours in the evening at a sub-optimal level, or to get an extra hour in bed and train for an hour at a greater intensity? In most cases, it is the latter.
Sleep is a multiplier that is applied to everything we do. So, surely, it is best to maximize the quality and the quantity of the sleep we get. Here's how to do just that.
WHEN SHOULD WE SLEEP?
The answer to this question comes from an answer to another question: "What are we?"
We are not owls or badgers; they are nocturnal, active during the night and sleeping during the day. We are not lions or fossa; they are cathemeral, flitting between day- and night-activity and daytime- and nighttime-sleep. We are not dogs, bears or snakes; they are crepuscular, active during the hours of twilight and at rest during the height of day and night. We are humans; diurnal, awake and active during the day and sleeping at night. We have evolved to sleep after the sun goes down and wake after it comes up, in line with what is called our "circadian rhythm".
Our circadian rhythm is an in-built biological clock, operating over a twenty-four hour period, that influences the functions of our mind and body. Of course, that's not the whole story: our circadian rhythm, while important, isn't the be-all-and-end-all of sleep. Local factors and environmental cues make subtle and significant alterations to our mental and bodily functions. For example, the further you live from the equator, the darker your winters will be. And dark winters usually mean that your body requires an extra hour of sleep each night. That desire to stay under the blankets on a cold winter morning isn't just laziness. Conversely, those living closer to the equator experience more sunlight and so feel the need to sleep less. These more temperate climes and the cultures that have evolved in them also tend to have a long tradition of napping: the Italian riposo and the Spanish siesta are just two responses to the reality of exceedingly high temperatures and lots of exposure to sunlight.
Chronotypes also affect circadian rhythms. With billions of humans, there's bound to be some variation in when people like to sleep. The idea that some people are "early birds" and some are "night owls" isn't make believe--it has sound scientific basis.
And don't forget the stubborn human desire to go against nature. Whilst monophasic sleep--one extended period of sleep in twenty-four hours--is still the norm (at least, it has been since the Industrial Revolution), we've also figured out alternatives. Biphasic sleep is the practice of splitting sleep into two periods over twenty-four hours. An example, common to the Mediterranean, is to sleep for five hours during the night and take a one-to-two hour nap in the afternoon. There's one more level, though. Polyphasic sleep, that takes the splitting of sleep to the extreme. Many polyphasic sleepers take a “core” sleep anywhere from ninety minutes to six hours and twenty-minute naps during the day.
Back to the question: When should we sleep?
First, after the sun goes down--we are diurnal animals who have evolved to sleep at night. Second, when you start to feel tired--in the evenings your biology will kick in and begin the wind-down process. Your mental alertness will begin to decrease and you'll begin to feel less energetic and more relaxed. In the absence of exceedingly bright lighting and without blue light from screen exposure, your body will send you signals that it's bedtime. And it will usually do this at around about the same time every day. Which is the third part of the answer:
Go to bed after the sun goes down, when you feel tired, and at roughly the same time each night.
Check back next week for part two, where I discuss the where and how of sleep, and recommend five simple things you can do to start improving it.