The risk of heart disease becomes greater the more an individual works outside of their natural body clock, new research suggests.
A study that focused on the role of circadian misalignment, the difference between the social clock and the individual biological clock, found that for each hour the work schedule was out of sync with an employee’s body clock, the risk of heart disease got worse.
Dr Sara Gamboa Madeira, of the University of Lisbon, Portugal, who presented her findings at the online ESC Preventive Cardiology 2021, said her study included 301 blue collar workers, all of whom worked in the distribution warehouses of a retail company in Portugal on early morning shifts from 6am-3pm; late evening shifts from 3pm-midnight; or night shifts of 9pm-6am.
Participants completed a questionnaire on sociodemographic factors, occupational factors and lifestyle factors and had their blood pressure and cholesterol measured.
The study used the Munich ChronoType Questionnaire to assess sleep duration, to estimate each individual’s chronotype, and to quantify the amount of circadian misalignment, also known as social jetlag.
Participants, whose average age was 33 and 56% of whom were men, were divided into three groups according to hours of social jetlag: two hours or fewer, two-four hours, and four hours or more.
The European relative risk SCORE chart was also used, which incorporates smoking, blood pressure and cholesterol to calculate relative cardiovascular risk.
Just over half (51%) of the participants were smokers, while 49% had high cholesterol, and 10% had hypertension.
One in five was classified as high cardiovascular risk and 40% slept less than six hours on workdays. The researchers found that the average social jetlag was nearly two hours. In 59% of workers, social jetlag was 2 hours or less, while for 33% of staff it was two-four hours, and in 8% it was four hours or more.
The team established that a higher level of social jetlag was significantly associated with greater odds of being in the high cardiovascular risk group, with the odds of increasing by 31% for each additional hour of social jetlag, even after adjusting for sociodemographic, occupational, lifestyle, and sleep characteristics and body mass index.
Dr Gamboa Madeira said: “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.
“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.”
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