“Human beings are daytime animals”, as explained by Maria Angeles Bonmati, postdoctoral researcher at CIBER (Carlos III Health Institute) and author of the book Let nothing take away your sleep (Criticism). That is, we are physiologically prepared to be active during the day and to rest at night. However, within this general pattern, adds Bonmati, “people can be classified into different chronotypes” based on their internal clocks, conditioned by their circadian rhythms. Simplifying, we can talk about people with an evening chronotype and people with a morning chronotype.
“A morning person tends to get up and go to bed earlier, and tends to prefer physical exercise first thing in the morning. In addition, he is usually hungrier when he gets up and therefore needs to have breakfast early. On the other hand, those in the evening, who tend to go to bed and get up later, may prefer to delay breakfast a bit or hold out with just a cup of coffee (those who drink it) and tend to prefer physical exercise in the afternoon”, Maria Jose Martinez explains. Madrid, coordinator of the Chronobiology working group of the Spanish Sleep Society, researcher at the University of Murcia and founding partner of Kronohealth, who adds that these preferences also apply at the cognitive level: people with a morning chronotype tend to prefer to get up early to study or perform any other activity that requires concentration or precision, while those with an evening chronotype prefer to do these activities at night.
Although, as Martinez Madrid acknowledges, to date there is not much scientific evidence on the direct relationship between chronotype and mortality, various studies, he points out, have observed a greater morbidity (proportion of people who get sick) associated with the evening chronotype that, “ hypothetically and ultimately”, could lead to an increase in mortality: “A direct relationship has been found between the evening chronotype and eating disorders (overweight, obesity, unhealthy metabolic biomarkers, etc.) or circadian disorders such as jet lagged social [el retraso considerable en la hora de acostarse y despertarse durante los dias festivos]. Furthermore, at a psychological level, the evening chronotype has been shown to be a risk factor for depressive disorders and substance use disorders, while the morning chronotype appears to act as a protective factor.”
This opinion is shared by Maria Angeles Bonmati, who points out that, although the evening chronotype had already been associated with a greater probability of presenting cardiovascular risk factors (such as obesity or tobacco use), the reality is that studies in this regard “showed an increase in mortality with the evening chronotype, regardless of these associated factors”. An increase in mortality that, to date, the researcher points out, had been related to an increase in behavioural, psychological and physiological risk factors, some of which could be attributed to a chronic mismatch between the internal physiological schedules of these people and socially imposed work schedules and activities. “In short, the ultimate cause might not be so much the evening chronotype per se such as jet lag or jet lagged social, to which people with this chronotype live for most of their lives”, he adds.
Now, a recent study published in the journal Chronobiology International with data obtained after a 37-year follow-up of more than 23,000 Finnish adults, has concluded that the higher mortality associated with the evening chronotype (estimated at 9% in the study) could be basically due to two bad habits: smoking and drinking. In fact, according to the study, in the case of non-smokers who, at best, are occasional drinkers, no association of the evening chronotype with mortality was found. “I think the most important message from our study is that night owls are not at increased risk of death. The chronotype is a personal characteristic, but for unknown reasons we see that unhealthy lifestyles seem to develop more frequently among night owls,” explains Jaakko Kaprio, professor at the Department of Public Health at the University of Helsinki and co-author of the study.
Among those reasons, he points to several hypotheses, including that night owls may have a tendency to stay up later at parties, pubs and bars and are therefore more likely to smoke and drink more; It could also be that, in an inverse relationship, these bad habits have the potential to change a person’s chronotype or that there are genes that affect both chronotype and alcohol consumption and smoking.
Along the same lines, Maria Angeles Bonmati, who points out that several studies had already shown that evening people, on average, show a greater probability of consuming more alcohol and being smokers than morning people, points out that an article was published in 2010 in which the authors suggested that an evening chronotype would not necessarily lead directly to greater mental imbalance, but that only those evening people who also smoke and drink would show lower scores in psychological well-being. “According to these authors, the frequent jet lag in people who work in the evening (forced to work in the morning during the week) would generate stress that some people compensate by smoking. Smoking, therefore, could be a way of coping with jet lagged social, similar to the higher consumption of other stimulants such as alcohol or caffeinated beverages”, he reflects.
For the author of Let nothing take away your sleep (Criticism), the Finnish study “breaks with previous evidence”, which showed an increase in mortality due solely to the evening chronotype in isolation, but qualifies that the study was carried out in a Finnish population, “with geographical and cultural characteristics , closely related to aspects that influence our physiology, which differ from those of other places”, therefore, in his opinion, “it would be risky to state emphatically” that there are no more risks associated with the evening chronotype than these bad habits: “There will be to continue investigating and studying other related aspects until the evidence is clear one way or the other.”
The social stigma of nightlife
For Jaakko Kaprio, when it comes to public health policies, it is important to know if an exposure or behavior (in this case the evening chronotype) that is associated with poor health, illness or death is a real cause or just an indicator or sign of warning correlated for some reason with the actual cause. “For example, having yellow fingers is associated with an increased risk of lung cancer, but it is not a cause of cancer. Yellow fingers are an indicator of heavy and prolonged smoking, the true cause of lung cancer. Launching a campaign for everyone to clean their fingers properly and regularly would not decrease lung cancer. Only quitting smoking (and preventing the initiation of smoking) would really reduce the risk of lung cancer”, he exemplifies before highlighting, in this sense, that the study findings provide reassurance to people who might worry about being of a chronotype nocturnal: “It is difficult to influence a person’s chronotype, but, conversely, most people can reduce their alcohol consumption and quit smoking. And if they can’t do it alone or with the support of family and friends, they should seek professional help.”
For Angeles Bonmati, for her part, although one must be prudent and wait for confirmation of these results in other populations “and with more precise chronotype evaluations” than those used in the research, the results of the study may lead to looking from another perspective. the supposed negative effect of the evening chronotype and emphasize that bad habits, avoidable in many cases, have a lot to say in these effects on health. “For now, it never hurts to try to make the population aware of the importance of avoiding tobacco and alcohol consumption,” she argues.
Lastly, Maria Jose Martinez Madrid recalls that, sometimes, people in the evening feel misunderstood and judged, a situation of vulnerability that can favor the consumption of substances such as tobacco and alcohol. “If there is not a direct and exclusive association between the chronotype and the increase in morbidity or mortality, it would be interesting to study more about why these people with evening time preferences acquire worse habits. In fact, we could ask ourselves questions such as whether the society is made exclusively for morning workers or if it is frowned upon to be an evening worker, as if it were a choice”, reflects the spokesperson for the Spanish Sleep Society. For her, “in an ideal situation”, one should consider, for example, as far as possible, “the time preference of each person to establish the different work shifts, so that there would be more job security, greater personal satisfaction , and therefore, higher productivity.
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Source: EL PAIS