Did you wake up feeling fresh and rejuvenated after a good and long night’s sleep this morning? If you’re like the majority in today’s high-tech, industrialized world, the answer to this question is probably no. Chronic insufficient sleep, insomnia, and other sleep-related problems are high up on the list of top health concerns for a great many people in the world today. This epidemic of poor sleep is largely the result of a discordance between today’s living conditions and our ancient genome; a genome that evolved for millions of years in environments that were devoid of smart-phones, artificial lighting, modern chronic stressors, and late night TV shows…
Traditional sleeping patterns
Studies of hunter-gatherers, pastoralists, and other non-industrialized societies show that these populations typically practise biphasic or polyphasic sleep, meaning that they sleep in two or more phases during the night (1, 2). Biphasic sleep is characterized by some time of wakefulness in between the first and second sleep, a period where it’s common to relax in bed, have sex, meditate, think about dreams, or communicate with other people.
The idea that biphasic (or perhaps polyphasic) sleep is normal for humans is supported by our long evolutionary history with this sleeping pattern, as well as research which shows that people tend to sleep biphasically when they are subjected to natural patterns of light and dark (3). However, it’s important to note that the sleeping pattern of various native populations around the world often differ markedly, which clearly shows that “the regulatory processes governing “sleep-wake transitions” could be shaped by cultural conditions” (4).
The Hadza are a group of hunter-gatherers that live in an area of the world where our species evolved, and as such, looking at their lifestyle gives us many hints as to how our late Paleolithic ancestors lived. These foragers typically go to bed at around 9.00 p.m, and they might wake up one or more times during the night before they get out of bed at dawn, which is between 6.30 and 7.00 a.m. at the equator (1). The Hadza hunter-gatherers sometimes also take a one- to two-hour midday nap (1).
For hunter-gatherers and other populations who live in more “ancestral settings”, it’s rare to sleep in isolation. Also, the sleeping environment tends to be rich in sensory inputs, such as the sparkling of the fire nearby, sounds from birds and animals living in the area, and noises from other people close by. Traditional populations often sleep on hard beds with negligible bedding, partly because this helps minimize fleas, bedbugs, and other parasites that can more easily set up shop in warm, big, and comfortable beds.
Light bulbs, TVs, and smart phones
In the late 1700th century the traditional pattern of segmented sleep started to disappear among the upper class in Europe, and over the subsequent centuries, this change gradually spread (2). Sleep patterns have changed dramatically everywhere that artificial lighting has been introduced, a transition that is characterized by a change from broken-up sleep to one period of sleep once every 24-hours.
Today, the norm in the industrialized world is to sleep in one concentrated bulk during the night, and some may even think that there’s something wrong with them because they can’t sleep for 8 straight hours. Also, as most people prefer to stay up long after the sun goes down, perhaps working late to maximize productivity, segmented sleep – at least in the way our ancestors did it – is not on the table as a viable option for most people.
The biological clock, which helps determine when we feel the need to wake up or go to sleep, is set by external signals such as light and darkness. Artificial lighting affects a person’s circadian rhythm and interferes with the secretion of melatonin, a hormone that plays an essential role in regulating sleep and wake cycles. Blue light – light with wavelengths in the 500nm to 381nm range – has an especially potent effect on the suppression of melatonin (4). This type of light is emitted by most of the electronics that are found in people’s homes, such as computer monitors and various gadgets.
The introduction of artificial lighting make people stay up longer, both because it gives us a way to see in the dark and also because light keeps us from getting tired. The Industrial Revolution transformed time. Many would say that the technological advancements that came with this revolution are among the greatest achievements in human history. However, the change wasn’t without its consequences, some of which are directly related to the amount and quality of sleep we get.
Recent research shows that a typical American sleeps for only 6.1 hours each night, 1 hour less than the national average in 1970, and between 2 and 3 hours less than ~100 years ago (1). Today, 63% of Americans report that their sleep needs are not being met during the week (5). Similar trends are seen in other parts of the world where artificial lighting and electronic devices have become a natural part of daily life.
Our living conditions have changed too rapidly for our bodies to keep up. Technological developments and cultural change have led us to abandon the types of sleeping patterns and conditions we evolved with for millions of years. This has resulted in an epidemic of sleep-related disorders.
The deleterious impact of poor and insufficient sleep
- When we sleep, many systems in our body are in a heightened anabolic state, a state that facilitates the repair and growth of the nervous, immune, and skeletal systems, among others. If we experience insufficient and/or poor sleep, these processes are jeopardized, and we get the familiar feeling of drowsiness, suboptimal physical performance, and brain fog.
- Sleep deprivation leads to increased production of cortisol, which can shift the body into the state of fright and flight by raising alertness and shuttling sugar into the bloodstream (3).
- Insufficient sleep can result in a variety of adverse physiologic effects, such as hypertension, activation of the sympathetic nervous system, impairment of glucose control, increased inflammation, and fat gain (partly by causing leptin levels to fall) (6, 7).
- Insufficient sleep and circadian rhythm disruption adversely affects gene expression and perturb the microbiome, which explains why sleep loss is a risk factor for many chronic diseases, including obesity and diabetes (8, 9, 10).
- Besides the impact on our general health, another saddening possibility is that our altered sleeping patterns have resulted in a state where we are missing out on “true” wakefulness during the day.
Strategies that can help you sleep more and better:
- The notion that sleeping 8 straight hours every night is the normal and/or optimal way to sleep has little evolutionary support. That said, from the perspective of getting the best possible sleep within the parameters of our modern lives, a concentrated bulk of 6-9 hours sleep each night is pretty good.
- If you have the opportunity and desire to sleep biphasically, there’s no reason not to do it.
- Keep to a routine.
- Reduce or eliminate your use of light-emitting electronics at night.
- Don’t work out right before bed. The short-term burst in cortisol can make it harder to sleep.
- Install f.lux (a program that makes the color of your computer’s display adapt to the time of day, warm at night and like sunlight during the day) or another similar program on your computer.
- Expose yourself to a lot of bright light during the day.
- Consider using amber goggles in the hours before going to bed.
- Sleep in a completely dark room.
- Avoid stressful activities before bed.
- Use a dawn simulator alarm clock.
- Consider listening to sounds of nature before bed.
- Nail down the rest of your lifestyle. E.g., physical activity, stress, sun exposure.