who are “more likely to have a heart attack or stroke”?

Researchers have found that working hours that deviate from a person’s natural body clock are associated with a higher risk of cardiovascular disease.

And the more shiftwork people do, the greater the risk of heart problems.

Study author Dr Sara Gamboa Madeira, from the University of Lisbon in Portugal, said:

“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.”

At least one in five employees work shifts, and a growing body of scientific evidence links shift work to heart health problems.

Several explanations have been proposed, including sleep disturbances and unhealthy eating habits.

The new study focused on role of circadian misalignment, or “social jet lag” – which is the difference between the individual “social clock” and “body clock”.

Dr Gamboa Madeira said:

“We all have an internal body clock that ranges from the morning types, or larks, who feel alert and productive in the early morning and sleepy at night, to the late types – the owls, for whom the opposite is true, with most of them. the population fall in between.

“Circadian misalignment occurs when there is a mismatch between what your body wants, for example, to fall asleep at 10 p.m., and what your social obligations require you to do, 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.). Participants completed a questionnaire on age, gender, education, work factors such as work schedule and length of service, and lifestyle factors, and had their blood pressure and cholesterol measured .

The questionnaire was used to assess the duration of sleep and to estimate the internal biological clock, also called chronotype. It has also been used to quantify the amount of circadian misalignment. Participants were divided into three groups based on social jet lag times: two hours or less, two to four hours, and four hours or more.

The researchers calculated the relative cardiovascular risk of each participant, taking into account smoking, blood pressure and cholesterol. They then investigated the association between social jet lag and high cardiovascular risk.

The average age of the participants was 33 and 56 percent were men. Just over half were smokers, 49% had high cholesterol, and 10% had high blood pressure. One in five people (20 percent) was classified as having high cardiovascular risk.

About 40 percent had a short amount of sleep – six hours or less – on work days. The average social jet lag was nearly two hours.

For most workers (59 percent), the social jet lag was two hours or less, while for one-third of staff (33 percent) it was two to four hours, and in about one in 12 people (8 percent) it was four 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 other factors such as lifestyle and body mass index.

Dr Gamboa Madeira added:

“These findings add to the growing evidence that circadian misalignment may explain, at least in part, the association between shiftwork and adverse health effects.

“The results suggest that staff with atypical work schedules may need closer monitoring of heart health. Studies are needed to determine whether late chronotypes better cope with late or night shifts and early chronotypes with early morning shifts, both psychologically and physiologically.

The results were presented at the virtual congress of the European Society of Cardiology.

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