In our 24-hour, digitally-connected world, sleep has become a neglected part of our daily schedule. Increasingly, people are sleeping less in order to keep up with the pace of modern life, while also having more trouble sleeping because of stress resulting from their busy schedules. In addition to being a biological necessity, sleep is important to our well-being. Sleep helps the growth and rejuvenation of our bodies, and getting enough sleep improves our memory, mood, and performance. Alternatively, cutting back on sleep makes us less productive and reduces our quality of life. In a world that is increasingly built for computers, we need to prioritize our biological needs, put down our electronic devices, and cut the power so we can get a good night’s rest.
A Brief History of Sleep
Our relationship to sleep changed with the advent of electricity. Before then people followed the cycle of the seasons in deciding when to get up and go to bed. When the sun came up it was time to start the day, and when it went down, it was time to eat and go to bed, because light sources were limited and weak (the fireplace, candles, and later kerosene lamps), and for those of humble means, expensive. People worked more in the summer, due to the longer days, and less in the winter. Most people were also employed in agriculture, which dictated the working schedule. What is surprising about traditional sleep patterns before the advent of gas lights and later, electricity, is that according to historian Roger Ekirch, people practiced segmented sleep, sleeping twice a night: once when it got dark for a few hours, waking up to eat, socialize, etc., before going back to sleep again until morning. This meant that they got more sleep than we do today with our later, electricity-abetted, bedtimes.
Let there Be Light
The first revolution in lighting happened in Paris in the mid-19th century with the installation of 15,000 gaslights by Baron Georges Eugene Haussmann, who was appointed by Napoleon III to modernize what would subsequently become known as the City of Lights. It is difficult for us today, accustomed as we are to electricity, to appreciate how this transformed social life and indeed the economy of Paris at the time. Now Parisians could walk on the great boulevards of the city at night, and shops could stay open late. Subsequently, with the invention of the incandescent light bulb by Thomas Edison in 1879, electricity was popularized. Like gas lights did for the Parisian streets, electric lighting allowed people to stay up late in their homes, forever altering our sleep patterns.
The biological underpinning of our sleep pattern is the circadian rhythm, which is a time interval of 24 hours that has been "observed in animals, plants, fungi and cyanobacteria." Circadian rhythms are vital for survival, as they influence sleeping and eating patterns, "core body temperature, brain wave activity, cell regeneration, and other biological activities of animals," including humans. While this rhythm is internal, it is influenced by external factors, particularly daylight, and also heat. In addition to allowing us to see, our eyes contain the photopigment melanopsin, which transmits information on the lengths of day and night to the cells in our hypothalamus, which results in the production of the hormone melatonin that sets our circadian clock. In other words, our internal clock is entrainable, meaning that it can be reset by these external stimuli. For example, when we travel across time zones we experience jet lag before our circadian clock entrains, or adjusts to the local time. While we are all subject to the 24-hour circadian rhythm, we have different patterns of sleeping and waking . . .