According to a recent poll, 18% of adults employed full-time in the US work more than 60 hours a week. Although these long hours may benefit pay packets, the same may not be said for heart health; a new study suggests long working hours may increase the risk of coronary heart disease.

Heart disease is the leading cause of death in the US, killing around 600,000 people every year. Coronary heart disease (CHD) is the most common form of the condition, responsible for around 380,000 of these deaths.

CHD occurs when plaque accumulates inside the coronary arteries - the arteries that supply the heart muscle with oxygen-rich blood. The plaque can harden or rupture over time, restricting or blocking blood flow. The heart muscle can then become weakened, leading to arrhythmias - irregular heart beats - and heart failure.

According to the research team, including senior author Dr. Yun-Chul Hong of the Medical Research Center and College of Medicine at Seoul National University in South Korea, past studies have linked long working hours to adverse health outcomes, such as hypertension, diabetes, sleep problems and poor psychological health.

“Working hours not only affect physical health outcomes, but also lifestyle conditions, such as dietary patterns, exercise, smoking habits, and alcohol consumption,” the researchers note. “It is highly probable that cardiovascular diseases are affected by overtime work, because the risk factors of cardiovascular diseases are influenced by working hours.”
Working 61-70 hours a week linked to 42% increased risk of CHD

In this study, recently published in the American Journal of Industrial Medicine, Dr. Hong and colleagues wanted to see how working hours affected the risk of CHD.

They assessed 8,350 participants aged 19 or over who were a part of the Korean National Health and Nutrition Examination Survey IV (2007-09).

The participants were asked about their working hours, general health and lifestyle factors, such as diet, exercise, smoking habits and alcohol consumption. They also underwent a physical examination, and their blood pressure, total cholesterol levels, fasting plasma glucose levels, triglyceride levels and high-density lipoprotein levels were measured.

The subjects’ 10-year risk of CHD was assessed using the Framingham risk model - a scoring system that uses an array of information to calculate an individual’s likelihood of developing cardiovascular diseases within a certain time period.

In detail, the team found that people with longer working hours had more risk factors for CHD. They had higher blood pressure, for example, higher cholesterol levels and were more likely to smoke.

“These findings indicate that long working hours have adverse effects on the cardiovascular system,” say the researchers.

The team says this could be because those who work fewer hours already have health problems. “Health limitations as well as advantages may have influenced how much people worked. Persons who have worse cardiac health may not work long hours,” they add.

They note that their study is subject to some limitations. For example, using the Framingham risk model could have led to an overestimation or underestimation of CHD risk, as it does not take into account genetic and lifestyle variations.

Furthermore, the researchers were not able to control for certain factors, such as poor mental health, which may have influenced the relationship between working hours and CHD risk.

The team notes, however, that their large sample size and the monitoring of longer working hours meant they were better able to assess the link between working hours and CHD, compared with other studies. They add:

Earlier this year, Medical News Today reported on a study claiming shift work may increase the risk of type 2 diabetes.

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Written by Honor Whiteman