Chronotype and health
Analysis of half a million genomes confirmed the depressiveness of "owls"
But I did not find any reliable connection with obesity and diabetes
Polina Loseva, "The Attic"
The tendency to early or late awakening – the chronotype – is determined not only by social, but also by genetic factors. After processing the data of almost 700,000 people, the researchers found 327 new genes associated with people belonging to "larks" or "owls". In addition, they clarified how these genes are associated with mental disorders: "larks" are not in danger, but "owls" are at risk of developing depression and schizophrenia.
A person's daily routine is determined not only by signals from outside, like sunlight, but also by an internal clock. This is a molecular mechanism that revolves in every cell of the body, and is accompanied by an increase and an increase in the concentration of certain proteins. However, the period of our internal day is not strictly equal to 24 hours, and they have to be synchronized with the help of a central clock – a group of neurons in the brain. For "owls", these hours are a little late: their internal period is longer and therefore it is more comfortable for them to get up later and move the beginning of their day forward. In "larks", on the contrary, these hours are in a bit of a hurry and, accordingly, the period is shorter, and it is easier for them to get up early.
People with a late, "owl" chronotype are more likely to be unhealthy: as we already knew from previous studies, they are at risk of obesity, diabetes and mental disorders. However, these data were obtained on small samples. To put all the dots over the "and", an international team of researchers analyzed the genomes of 697,828 people. They compiled this sample from two large databases of genetic data: the British Biobank UK program and the 23andMe genetic testing service. Both groups of subjects have their drawbacks: the Biobank program was attended mainly by healthier Britons than the average population. As for 23andMe, their clients are mostly affluent white Americans.
Scientists were looking for correlations between variants of individual genes and the chronotype of the subjects, as well as the state of their physical and mental health. They were able to detect 351 genes associated with the chronotype (until now, only 24 such genes were known). Many of these genes are involved in the brain (in particular, the central clock in the hypothalamus) and reactions to light. In addition, the chronotype was also associated with genes that regulate metabolism: appetite, insulin secretion, and even sensitivity to nicotine and caffeine. However, all these genes have nothing to do with the quality and duration of sleep: people sleep equally well or poorly regardless of the comfortable time of awakening.
As for the connection of chronotype genes with the risk of developing mental disorders, previous estimates have been confirmed here. The strongest connection was between the early chronotype ("larks") and good mental health, as well as the late chronotype and schizophrenia, depression and increased intelligence. At the same time, the authors made an attempt to establish a causal relationship between these signs. Among people suffering from schizophrenia and depression, they did not reveal a strong bias towards early or late awakening. Therefore, they believe that it is not mental disorders that bring down the daily routine, namely the tendency to live in the dark can provoke diseases.
But for metabolic disorders, such as obesity and diabetes, it was not possible to separate cause and effect. The authors did not find any evidence that the chronotype affects the risks of such diseases. In this regard, they suggest that the reason for the disturbed metabolism may not be the chronotype as such, but the discrepancy between the comfortable chronotype and the real daily routine.
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