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to their SCN—which can occur for a variety of reasons, including tumors, brain trauma, and certain degenerative diseases—tend to sleep at odd times. But unlike jet lag, that’s not something that will correct itself; the person’s sleep times are thrown off because the “master clock” is broken. This tells us that, while the circadian rhythmmay be innate, it’s not permanently fixed. In fact, humans have been slowly but surely adjusting their circadian rhythms for generations. While you hear a lot of talk about the “sleep crisis” these days, the roots of the problem actually stretch back to the early nineteenth century and the invention of electric light. Before electricity use became widespread, people only had tools like candles and oil lamps to push away the darkness. Could you stay up late by candlelight? Of course you could, and people did all the time. But candles can’t turn a dim room into a bright one, or a dark street into a lit one, in the way that electricity can. Consider: it takes 100 candles to match the amount of light generated by one 60-watt bulb. The result is that electricity has enabled us to extend the day far beyond what our circadian rhythm would naturally suggest. It’s no accident that New York City gained its nickname “the city that never sleeps” in the early years of the twentieth century. In 1912, a newspaper in Fort Wayne Indiana suggested that people should “add to [New York City’s] title of the city that never sleeps that of the city that never grows dark .” The two ideas—absence of light and absence of sleep—are intimately connected due to the impact of light on our circadian rhythms. These days, the presence of what is called “blue light” has complicated the situation even further (see chapter 4 for ways of dealing with blue light).

Teen Guides to Health & Wellness: Sleep and Hygiene

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