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Scientists call the lark the kind of person who gets up easily and is more productive in the morning. Their chronotype – it's the technical name for each mode of sleep and activity – is the opposite of that of the owls, who work best at night and go to bed and get up late, in accordance to social conventions. A new study, released Tuesday in Nature Communications, reveals that people genetically programmed to wake up early are less likely to suffer from mental illnesses such as depression or schizophrenia. In addition, they say they feel better than others
It was known that the genetics of each individual condition their ability to follow one era or another. But previous research had identified only a handful of genes relevant to the chronotype, and studies that sought to link to health found only correlations, not causality. The new study, which examined the genome of 697,828 people, concludes that there are at least 351 genes that predispose a person to become an owl or lark, hundreds more than the 24 known. The researchers were able to establish a cause-and-effect relationship between being an early bird and better mental health.
The international research team led by biologists from the University of Exeter (UK). badyzed the genomes of British citizens gathered in the British Biobank research database as well as data from the private American company 23andMe, which sells genetic tests of people. Each participant had previously indicated their sleep patterns in a survey. However, scientists were looking for a more objective measure of chronotype and therefore included in the badysis the data of 85,760 people whose sleep hours were recorded with an activity bracelet.
The study confirms that those who were genetically predisposed to be larks slept an average of 25 minutes earlier than owls. They obtained this measure by comparing the 5% of people who had more morning genes in their DNA with the 5% who had fewer genes in their DNA. The difference in time between one end of the spectrum and the other seems modest, but it is statistically significant. However, there was no difference in the duration or quality of sleep.
Although the mornings say that they have a better general well-being and that there have been fewer cases of depression and schizophrenia, the researchers have found no evidence of the getting up early protects against other diseases, such as diabetes or obesity. "It was a bit surprising," says biologist Samuel Jones, of Exeter University, one of the authors of the study. "A lot of research has shown that owls have lower metabolic regulation and may be at risk for diabetes and obesity, but these studies tend to be correlated, so we could deduce the cause and the likelihood that they will be overweight." 39th effect. "
Social jet lag
One possibility to explain past results is that there is a third common factor for late sleep and for those who suffer from these diseases, explains Jones. But it is also possible that being an owl is not inherently bad for your health, but that it is detrimental to get up early for social and professional commitments when genetics predisposes you to the contrary.
In fact, many genes identified in this study are responsible for regulating circadian clocks of the body, biochemical processes that govern periodicity. cellular activities. Jones notes that "the circadian rhythm can be driven to a certain extent", especially when trying to maintain a routine to lie down and wake up at the same time. "If you are a person of the night, you may be able to walk a long way in the morning," says the researcher. But he adds, "The genes will stop you in the last step, because owls have an internal clock that works a little slower.This is genetic and can not be changed."
Worse, it's to get up early for social and professional commitments when genetics predisposes him to the contrary.
Maria José Martínez, coordinator of the chronobiology group of the Spanish Society of Sleep. SES), who did not participate in the study, states that "if we lived in a society in which everyone could organize their schedule (work, sleep, etc.) freely, it would be indifferent that health be morning or evening ". But Martinez, who is also director of the Kronohealth circadian consulting company, points out that this only happens for owls "provided that intense artificial light is used during waking hours and that light is avoided during the hours of sleep "[19659003] The incidence of light is an important factor because it stops the production of melatonin, a hormone that promotes sleep. A tip for advancing the routine when the body does not ask for it is to expose it to natural light or to the lamp early in the morning before even waking up. Curiously, Jones and his colleagues discovered that some of the 351 genes badociated with the chronotype are expressed in retinal cells of the eye, suggesting that "larks probably perceive light in a slightly different way than owls ", according to the author.
Other identified genes are expressed in the hypothalamus, a region of the brain that regulates sleep and wakefulness, some participate in insulin metabolism and some influence treatment stimulating substances such as caffeine. and nicotine. All of this highlights intrinsic physiological differences between owls and larks, but detailed studies are needed to determine how and why this affects each of these genetic variants of the chronotype and, by extension, mental health.
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