Working out of sync with body clock can risk heart health, study shows

New research offers a reason why you may not want to spend too much time working outside a typical work shift.

According to the European Society of Cardiology, working during hours that are not in line with your body clock can pose a risk to your cardiovascular system.

“Our study 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,” said study author Dr. Sara Gamboa Madeira of the University of Lisbon, Portugal, in a press release.

The body clock is the biological clock, or circadian rhythm, which Michigan Medicine reported is the 24-hour cycle that may be impacted by darkness and light. This can make the body think it’s time to sleep or awake. Along with body temperature, hunger and the immune system, the body clock controls when you sleep and wake up.

A 2019 HealthDay report noted that as many Americans turn in for the night, more than 2 million others are clocking into work.

“I just never seem to get enough sleep,” said Jennifer Salazar-Biddle, an aircraft mechanic who told the publication that getting six hours of sleep is considered a “good day.” For the married mother of a then-2-year-old, she said seeping during the day appears “unnatural.”

The current study from the ESC zeroed in on the part of circadian misalignment plays in the body. It is the difference between the “social clock,” such as when people work, and an individual’s “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,” Gamboa Madeira said. “Circadian misalignment occurs when there is a mismatch between what your body wants (e.g. to fall asleep at 10 p.m.) and what your social obligations impose on you (e.g. work until midnight).”

Researchers gathered 301 blue-collar workers for the study. All workers carried out picking activity in the distribution warehouses of a Portugal-based retail company by hand. Staff consistently worked from 6 a.m. to 3 p.m, 3 p.m. to midnight or 9 p.m. to 6 a.m. They filled out a survey about education, sex and age as well as work schedule and seniority. The questionnaire also included information about their lifestyle factors, and they had their blood pressure and cholesterol measured.

The study also used the Munich ChronoType Questionnaire to evaluate how long participants slept and their individual internal biological clock. This was used to evaluate social jet lag. Researchers separated participants into three groups according to hours of social jetlag: 2 hours or under, 2–4 hours and 4 or more hours.

Using the European relative risk SCORE chart to determine relative cardiovascular risk, researchers considered a relative risk of 3 or over as “high cardiovascular risk.” Then, they examined the link between social jetlag and high cardiovascular risk.

It was found that 20% had high cardiovascular risk. Around 40% had 6 hours or less of sleep. On average, social jetlag was almost 2 hours. The majority of workers — 59% — had 2 hours or less of social jetlag. Meanwhile, 33% of workers had 2-4 hours of social jetlag, and 8% had 4 hours or more.

The more social jet leg workers faced, the greater the chances they had of being in the high cardiovascular risk group. For each additional social jetlag hour, there was a 31% increase risk of being classified as high cardiovascular risk. This was the case when adjusting for sleep, lifestyle, occupational and sociodemographic attributes and body mass index.

“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,” 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.”