According to a study presented at ESC Preventive Cardiology 2021, an online scientific congress of the European Society of Cardiology (ESC), working hours that deviate from an individual’s natural body clock are associated with risk higher cardiovascular.
“Our study found that for every hour the work schedule was not synchronized with an employee’s body clock, the risk of heart disease worsened,” said the study author, Dr Sara Gamboa Madeira, University of Lisbon, Portugal.
At least 20% of European employees work atypical hours or shifts, 2 and a growing body of scientific evidence links them to deleterious cardiovascular effects.3 A number of explanations have been proposed, including sleep disturbances and unhealthy behaviors. This study focused on the role of circadian misalignment, which is the difference between the “social clock” (eg work schedules) and the individual “body clock”.
Dr Gamboa Madeira explained: “We all have an internal biological clock that ranges from morning types (larks), who feel alert and productive in the early morning and drowsy at night, to late types (owls), for whom the opposite is true. is true – most of the population falling in between. Circadian misalignment occurs when there is a mismatch between what your body wants (such as falling asleep at 10 p.m.) and what your social obligations impose on you (such as working until midnight). “
The study involved 301 blue-collar workers, all of whom were engaged in manual picking in the distribution warehouses of a retail company in Portugal. Staff always worked early in the morning (6 a.m. to 3 p.m.), late at night (3 p.m. to midnight), or at night (9 p.m. to 6 a.m.). The participants completed a questionnaire on socio-demographic factors (age, sex, education), professional factors (work schedule, seniority) and factors related to lifestyle and had their blood pressure and cholesterol measured.
The Munich ChronoType questionnaire was used to assess the duration of sleep and to estimate the internal biological clock of each individual (also called a chronotype). It has also been used to quantify the amount of circadian misalignment (i.e. the lag between an individual’s body clock and work hours) – called social jet lag. Participants were divided into three groups according to social jet lag times: 2 hours or less, 2-4 hours, 4 hours or more.
The researchers used the European Relative Risk SCORE graph which incorporates smoking, blood pressure and cholesterol to calculate the relative cardiovascular risk. The relative risk ranges from 1 (non-smoker with healthy blood pressure and cholesterol) to 12 (a smoker with very high blood pressure and cholesterol). In this study, a relative risk of 3 or more was considered “high cardiovascular risk”. The researchers then studied the association between social jet lag and high cardiovascular risk.
The average age of the participants was 33 years old and 56% were men. Just over half (51%) were smokers, 49% had high cholesterol, and 10% had high blood pressure. One in five people (20%) has been classified as having high cardiovascular risk. About 40% had a short amount of sleep on work days (6 hours or less). The average social jet lag was almost 2 hours. For most workers (59%), the social jet lag was 2 hours or less, while for 33% of staff it was 2 to 4 hours, and in 8% it was 4 hours or more.
A higher level of social jet lag was significantly associated with a greater likelihood of belonging to the high cardiovascular risk group. The odds of being classified as high cardiovascular risk increased by 31% for every additional hour of social jet lag, even after adjusting for socio-demographic, work-related, lifestyle, sleep, and body mass index characteristics.
Dr Gamboa Madeira said: “These findings add to the growing evidence that circadian misalignment may explain, at least in part, the observed association between shiftwork and adverse health effects. Results suggest that staff with atypical work schedules may need closer monitoring for Longitudinal studies are needed to determine whether late chronotypes better cope with late / night shifts and early chronotypes with morning shifts, both psychologically and physiologically. “
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