Research into chronotypes helps explain why people have natural sleep patterns, how that changes throughout life, the differences in circadian rhythms between men and women, and what we can do to modify our schedules. The biggest external factor is exposure to light, especially sunlight. As chronobiologist Till Roenneberg explains in his book, " Internal Time: Chronotypes, Social Jet Lag, and Why You're So Tired," the internal factors determining when we like to wake up are primarily genetic. That means that we're not all meant to be morning people. The answer is simple: Everyone has a natural internal clock - a chronotype or circadian rhythm - that determines when they're most alert and most sleepy. "Despite all the other contributors to variation, the genetic effect still shines through," Jun Li, a geneticist at the University of Michigan who was not involved in the study, told Live Science.Early risers are often glorified - there's the well-known saying about the early bird catching the worm, and many articles, blog posts, and Reddit threads about the benefits of getting up at 4:30 a.m.īut if rising early is so good for us, why don't all humans get up at the crack of dawn - or at least try to? Why do some of us consider ourselves morning people (also known as larks) or night owls? Geneticists, however, say that a large study like this could help boost researchers' confidence in the statistical significance of the genetic impact on circadian rhythms. But, changing life circumstances and exposure to light - such as sitting in front of a computer in an office late at night, or going for a hike on a vacation - can change whether someone is a morning person or a night person, according to Roenneberg. Being born with a predisposition toward waking early or sleeping in may make it more difficult for people to change their circadian rhythm. That's what allows people to recover from jet lag, or work as flight attendants and shift workers, Roenneberg said. Moreover, circadian rhythms are adaptable. Although it can be assessed by certain questionnaires, simply asking people whether they consider themselves morning or night people will not provide an objective chronotype, he added. How circadian rhythm manifests itself depends on a number of factors, such as sunlight and temperature, as well as genes, Roenneberg said. There are very, very short people, very, very tall people, and the rest are in between." "There aren't two shoe sizes and there are not just two body heights. "It is a continuous trait, as is body height or shoe size," Roenneberg told Live Science. And people over 60 said they preferred mornings more than those under 30 (63.1 percent, compared with 24.2 percent of participants under age 30), the researchers said.īut the distinction between being a morning person or an evening person isn't quite so simple, according to Till Roenneberg, a professor at Ludwig-Maxmilian University in Munich, Germany, who studies circadian rhythm. Women were more likely to be early risers (48.4 percent, compared with 39.7 percent of men). The scientists found that having one of 15 genetic variants increased a person's chances of being a morning person by between 5 percent and 25 percent, according to the study. By comparing the survey responses with information from the participants' DNA, the scientists were able to analyze whether any single base-pair mutations - called single nucleotide polymorphisms, or SNPs - showed up more frequently in people who identified themselves as being a morning person.
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