Were we meant to sleep in two chunks?
…Ekirch somehow rediscovered a fact of life that was once as common as eating breakfast. Every night, people fell asleep not long after the sun went down and stayed that way until sometime after midnight. This was the first sleep that kept popping up in the old tales. Once a person woke up, he or she would stay that way for an hour or so before going back to sleep until morning— the so-called second sleep. The time between the two bouts of sleep was a natural and expected part of the night and, depending on your needs, was spent praying, reading, contemplating your dreams, urinating, or having sex. The last one was perhaps the most popular.
So researchers did a study. When subjects had no exposure to artifical light they reverted to this 2 stage type of sleeping:
Soon, the subjects began to stir a little after midnight, lie awake in bed for an hour or so, and then fall back asleep again. It was the same sort of segmented sleep that Ekirch found in the historical records. While sequestered from artificial light, subjects were shedding the sleep habits they had formed over a lifetime.
Was this fragmented sleep bad? Far from it. Bloodwork showed that the time between the two sleeping periods was incredibly relaxing and blissful:
The results showed that the hour humans once spent awake in the middle of the night was probably the most relaxing block of time in their lives. Chemically, the body was in a state equivalent to what you might feel after spending a day at a spa… Numerous other studies have shown that splitting sleep into two roughly equal halves is something that our bodies will do if we give them a chance. In places of the world where there isn’t artificial light— and all the things that go with it, like computers, movies, and bad reality TV shows— people still sleep this way.
So why don’t we sleep like this? Lightbulbs.
Electric light at night disrupts your circadian clock, the name given to the natural rhythms that the human body developed over time. When you see enough bright light at night, your brain interprets this as sunlight because it doesn’t know any better… your body reacts to bright light the same way it does to sunshine, sending out signals to try to keep itself awake and delay the nightly maintenance of cleanup and rebuilding of cells that it does while you are asleep. Too much artificial light can stop the body from releasing melatonin, a hormone that helps regulate sleep.
And as I’ve posted before, all this artificial light may be responsible for some of our more modern health issues:
Circadian rhythms— which you will learn much more about in a later chapter— are thought to control as many as 15 percent of our genes. When those genes don’t function as they should because of the by-products of artificial light, the effects are a rogue’s gallery of health disorders. Studies have linked depression, cardiovascular disease, diabetes, obesity, and even cancer to overexposure to light at night. Researchers know this, in part, from studying nurses who have spent years working the graveyard shift. One study of 120,000 nurses found that those who worked night shifts were the most likely to develop breast cancer.