The study of 85,000 men and women showed that compared to individuals who work a normal week of between 35-40 hours, those who worked 55 hours or more were about 40 per cent more likely to develop atrial fibrillation during the following ten years. For every 1,000 people in the study, an extra 5.2 cases of atrial fibrillation occurred among those working long hours during the ten-year follow up. Atrial fibrillation (AF) is a heart condition that causes an irregular and often abnormally fast heart rate.
During the ten-year follow-up period, there were 1,061 new cases of atrial fibrillation. This gave an incidence rate of 12.4 per 1,000 people in the study but among the 4.484 people working 55 hours or more the incidence was 17.6 per 1,000.
Professor Mika Kivimaki, from the department of epidemiology at University College London, said: “Those who worked long hours had a 1.4 times higher risk of developing atrial fibrillation, even after we had adjusted for factors that could affect the risk, such as age, sex, socioeconomic status, obesity, leisure time physical activity, smoking and risky alcohol use.”
He added: “The great strength of our study was its size, with nearly 85,000 participants, which makes it large by the standard of any study in this field. Obviously, monitoring of working hours over several years would be more ideal than a one-off measurement at the start of the study. However, I do not think the results would have been dramatically different with repeat measurements of working hours because people tend to keep their working patterns.”
The study does have some limitations, including the fact that working hours were only assessed once at the beginning of the study and that the type of job, for instance whether it involved working night shifts, was not recorded.
Professor Sir Nilesh Samani, medical director at the British Heart Foundation, said: “Atrial fibrillation is a common heart rhythm disorder that affects over one million people in the UK and which increases the risk of stroke. Although we know some of the causes of atrial fibrillation, such as age, high blood pressure, heart valve disease and excess alcohol consumption, many patients develop the condition without an obvious cause.
“The suggestion that longer working hours may be a cause of atrial fibrillation is very interesting. Significantly, this study clearly shows that the link between atrial fibrillation and long working hours has nothing to do with the other, already known, risk factors for the condition.”
Andrea Cail, director of the Stroke Association in Scotland, said: “These latest findings suggest that working long hours could be linked to an increased risk of developing AF. It is hard to say what might cause this link between long working hours and AF.
“However, we do know that around 50,000 people in Scotland are living with undiagnosed AF, putting them in danger of a stroke. And 8,077 people in Scotland who are already known to have AF do not receive the medication they need to manage the condition.”