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.”
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 risk of CHD increases after the age of 45 for men and 55 for women
- One of the most common symptoms of CHD is angina – chest pain or discomfort caused by lack of oxygen-rich blood reaching the heart muscle
- Some people with CHD can treat the condition simply by making lifestyle changes, such as following a healthy diet and increasing exercise.
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.
The researchers found that the longer hours participants worked, the more likely they were to develop CHD within 10 years. Those who worked 61-70 hours a week were at 42% higher risk of CHD than those who worked 31-40 hours a week. Participants who worked 61-70 hours a week had a 63% increased risk of CHD, while those who worked more than 80 hours a week had a 94% higher risk.
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.
However, the team was surprised to find that compared with participants who worked 31-40 hours a week, those who worked less than 30 hours a week had higher blood pressure and higher total cholesterol levels, which represented a higher 10-year risk of CHD.
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:
“In conclusion, working long hours is associated with an elevated risk for CHD based on the data representative of the Korean adult population. We hope that these ﬁndings contribute to the proper management of working conditions and enhance quality of health care for workers, particularly for those at risk for CHD.”
Earlier this year, Medical News Today reported on a study claiming shift work may increase the risk of type 2 diabetes.