Misaligned body clock impacts heart health in shift workers

Working hours that deviate from an individual’s natural body clock are associated with greater cardiovascular risk, with shift workers being particularly susceptible. That’s according to new research presented at ESC Preventive Cardiology 2021, an online scientific congress of the European Society of Cardiology (ESC).

At least 20% of European employees work atypical hours or shifts, and growing scientific evidence associates these with deleterious cardiovascular outcomes. A number of explanations have been proposed, including sleep disruption and unhealthy behaviours. The new study focused on the role of circadian misalignment, which is the difference between the ‘social clock’ (eg, work schedules) and the individual ‘biological clock’.

“We all have an internal biological clock which ranges from morning types (larks), who feel alert and productive in the early morning and sleepy in the evening, to late types (owls), for whom the opposite is true — with most of the population falling in between,” said study author Dr Sara Gamboa Madeira, from the University of Lisbon. “Circadian misalignment occurs when there is a mismatch between what your body wants (eg, to fall asleep at 10 pm) and what your social obligations impose on you (eg, work until midnight).”

The study included 301 blue-collar workers, all performing manual picking activity in the distribution warehouses of a retail company in Portugal. Staff always worked either early-morning (6 am–3 pm), late-evening (3 pm–midnight) or night (9 pm–6 am) shifts. Participants completed a questionnaire on sociodemographic factors (age, sex, education), occupational factors (work schedule, seniority) and lifestyle factors, and also had their blood pressure and cholesterol measured.

The Munich ChronoType Questionnaire was used to assess sleep duration, and to estimate each individual’s internal biological clock (also called chronotype). It was also used to quantify the amount of circadian misalignment, referred to as social jetlag. The SCORE chart, which incorporates smoking, blood pressure and cholesterol, was meanwhile used to calculate relative cardiovascular risk on a scale of one to 12, with the researchers judging that a relative risk of three or more was considered ‘high cardiovascular risk’.

A higher level of social jetlag was significantly associated with greater odds of being in the high cardiovascular risk group, the researchers found. The odds of being classified high cardiovascular risk increased by 31% for each additional hour of social jetlag, even after adjusting for sociodemographic, occupational, lifestyle and sleep characteristics as well as body mass index. In most participants (59%) social jetlag was two hours or less, while for 33% it was 2–4 hours and in 8% it was four hours or more.

“These results add to the growing evidence that circadian misalignment may explain, at least in part, the association found between shift work and detrimental health outcomes,” Dr Gamboa Madeira said. “The findings suggest that staff with atypical work schedules may need closer monitoring for heart health. Longitudinal studies are needed to investigate whether late chronotypes cope better with late/night shifts and earlier chronotypes to early morning schedules, both psychologically and physiologically.”

Image credit: ©stock.adobe.com/au/auremar

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