Sleep disorders and bad habits: here are the harmful effects of shift work on health | health and wellbeing


More than three and a half million employees work in shifts in Spain, and about two million (10.6% of employed people) occasionally work in night shifts (6%) or more than half of the working days (4.6% ), according to data from the National Institute of Statistics for 2021. Shift work, especially the night shift or the one that includes it in the rotation, has been marked in red by the health authorities for some time. In 2019, the International Agency for Research on Cancer (IARC) placed night work in evidence group 2A of its classification “probably carcinogenic to humans”. “At the same level as tobacco!” », exclaims on the other end of the line Dr. Juan Antonio Madrid, professor of physiology and director of the Chronobiology Laboratory of the University of Murcia (IMIB-Arrixaca, CIBERFES), who considers that there is enough experimental evidence in animals and indirect evidence in humans to support this relationship. And not only, since, as Madrid explains, the chronic alteration of all the biological rhythms involved in shift work has an enormous impact on health: “The release of inflammatory mediators is exacerbated, the activity of the immune system decreases, it has an effect at the metabolic level that can lead to prediabetes, higher levels of triglycerides, cardiovascular alterations (hypertension), a higher risk of suffering from myocardial infarction and stroke, etc. In short , it aggravates a wide variety of very important pathologies”.

This assignment is maintained in the long term, even after leaving shift work. This was shown in a study on mice recently published in the scientific journal Neurobiology of sleep and circadian rhythms, the results of which confirm that the effects of shift work schedules in early adulthood (equivalent to 18-24 years of human age) persist until middle age (55-60 years) even after returning rodents at a normal schedule during the interim period. “We found that exposure to shift work schedules in early adulthood exacerbates midlife ischemic stroke outcomes, particularly in women. Moreover, even when study subjects returned at a normal schedule, the effects on sleep-wake rhythms of early exposure to shift work cycles persisted, such that by middle age these subjects woke up earlier and were activated at the wrong time day and night,” says David J. Earnest, principal investigator and professor at the Texas A&M University Center for Biological Clocks Research, at EL PAÍS.

For Juan Antonio Madrid, these data are “interesting” because they dismantle the idea that the effects of shift work are punctual and disappear when a more regular normal schedule is found. “We know that the incidence of cardiovascular disease among the population working shifts is around 20%, compared to 7% in the case of workers with daytime schedules. In the case of former shift workers, the risk percentage remains at 15%. Shift work time – if it’s long, not if we’re talking about one or two years – leaves traces and leads to alterations that are not completely reversible”, maintains the professor, who specifies that since it is an investigation in mice, the extrapolation of data to humans is risky, but it “offers clues as to where the mechanisms go” and the advantage that in rodents confounding factors are eliminated, since the shift work in men (especially night work) is also associated with poorer lifestyle habits (more sedentary lifestyle, more tendency to use tobacco and alcohol, poorer diet)” which may mask and aggravate the health risks of a shift worker and which are not solely due to the working hours”.

Is it possible to adapt to the night work schedule?

A study published in July in the journal eBioMedicine (The Lancet), dismantles with its results another myth associated with night work: the one that defends that “we get used to everything and that the body adapts to everything”. For the research, the authors followed 63 night workers (working three nights or more for 10 hours a week) and 77 workers who alternated morning and afternoon shifts, all employed at Paul-Brousse Hospital. , located on the outskirts of Paris. . The results were not misleading: shift workers saw significant declines in sleep quality and circadian rhythms. And that despite having been on that same night shift for over five years. “One of our most surprising findings was the poor adaptation of the circadian system of these hospital workers to night work, even though they had been on this shift for a long time. And this effect was not only observed working days, but also rest days, which indicates that some night workers do not even regain normal circadian function on their rest days,” explains Francis Lévi, research director in the Chronotherapy, Cancers and Transplantation group. . from the Faculty of Medicine of the University of Paris-Saclay.

“Biological clocks are primed to anticipate, to prepare the body for all regular and predictable events. If we don’t provide that predictable framework, the body is unprepared.”

“It is almost impossible to adapt to night work”, endorses Juan Antonio Madrid, who considers that this adaptation is only viable in isolated environments such as oil rigs, where night workers can maintain more regular hours. . “The problem is the chaotic habits, the fact that one day you eat at one time and the next day at another, that one day you activate your body to exercise at one time and the next day at other, that one day you go to bed at a certain time and the next at another. Biological clocks are primed to anticipate, to prepare the body for all regular and predictable events. If we don’t provide this predictable framework, the body is not prepared”, he argues.

Despite this virtual impossibility, the professor from the University of Murcia points out that three basic strategies can be followed to try to minimize as much as possible the impact of shift work on rest and on the circadian clock. The first strategy, how could it be otherwise, is regularity: “You have to regularize your meal and sleep times as much as possible, because if you have a night job, but on the days you work, you completely change your schedule to attend family or social obligations, you continually change your schedules and this is negative, much more aggressive for our body than if we are able to maintain a delayed sleep schedule every day, whether we work or not. We must ensure that there is a common sleep band every day, that there are at least four hours of stable sleep. The key is to succeed in being regular with work schedules that encourage irregularity”.

The second strategy is that of contrast, which consists of practicing a physical activity (“because it makes you more resistant to the harmful effects of shift work”) and exposing yourself to natural light for part of the day, because sunlight is a powerful regulating biological agent. Finally, the most challenging yet, try to synchronize mealtimes/fasting times with sleep/dark cycles: “Fasting has to coincide with the sleep/dark center of your life, which is quite a challenge for someone one who works at night,” maintains Madrid.

Professor Francis Lévi, finally, highlights the need for night workers to be able to benefit from “specific medical assessments throughout their professional life” because they are exposed to greater health risks. “Today, it is possible to objectively assess sleep and circadian health in near real-time and non-invasively, designing preventive measures for individual workers if necessary and evaluating their effectiveness,” he concludes. .

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