Circadian Misalignment in Shift Workers Linked With High Cardiovascular Risk

For each hour that an employee’s work schedule deviated from their natural body clock, their odds of having high cardiovascular risk increased by 31%.

Shift work that impacts an individual’s circadian rhythm may significantly increase their risk of cardiovascular disease, according to an abstract presented at ESC Preventive Cardiology 2021, from the European Society of Cardiology (ESC).

As workers undertake shifts that coincide or disrupt their natural body clock, researchers say this can lead to circadian misalignment, also known as social jetlag, which serves as the difference between their workday sleep behaviors and work-free day health behaviors, including tobacco and alcohol use, and exercise.


"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 author Sara Gamboa Madeira, PhD, of the University of Lisbon, Portugal, in a statement.

The impact of shift work and irregular work schedules have been indicated in prior research to be associated with several adverse health conditions, including type 2 diabetes, excessive daytime sleepiness, and hypertension.

Seeking to examine the association between social jetlag and cardiovascular risk in a cohort from Europe, whose workforce includes more than 20% of shift workers, researchers conducted a cross-sectional observational study of blue-collar shift workers (N = 301; 56.1% men; mean [SD] age, 33 [9.4] years) who either worked early morning, late evening, or night shifts.

Participants answered a self-questionnaire to gauge social jetlag and health behaviors, called the Munich Chronotype Questionnaire. Data were also derived on absenteeism, productivity, and seniority via company records, and on blood pressure and cholesterol via capillary blood samples.

Using the European relative risk Systematic COronary Risk Evaluation (SCORE) chart, participants were classified on their risk of cardiovascular disease, with a score of 3 or more indicating high risk.

In assessing the study cohort, 50.5% were smokers, 48.8% had hypercholesterolemia (≥ 190 mg/dL), and 10.6% had hypertension (≥ 140/90 mm Hg). The average (SD) sleep duration was 6 hours, 25 minutes (1 hour, 27 minutes), and the average social jetlag was 1 hour, 57 minutes (1 hour, 38 minutes).

On workdays, 40% of participants reported sleeping 6 or fewer hours, with 59.4% reporting social jetlag of 2 hours or less and 8% reporting social jetlag greater than 4 hours.

After adjusting for sociodemographic, occupational, lifestyle, and sleep characteristics, each hour of social jetlag was associated with a 31% increase in the odds of being classified with high cardiovascular risk (odds ratio, 1.31; 95% CI, 1.02-1.68; P = .033).

Overall, 39.5% had a risk score of 1, 40.2% had a risk score of 2, and 20.3% had a high risk score of 3 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,” said Madeira. “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."

Reference

Madeira SG, Reis C, Paiva T, Moreira C, Roenneberg T. Circadian misalignment is associated with a high cardiovascular risk among shift workers: is this an opportunity for prevention in occupational settings? Presented at: ESC Preventive Cardiology 2021; April 15-17, 2021.