July 14, 2017

expert reaction to study looking at working hours and atrial fibrillation

Publishing in the European Heart Journal scientists report that people who work long hours have an increased risk of developing an irregular heart rhythm known as atrial fibrillation.

Dr Graham Wheeler, Bayesian Medical Statistician, UCL, said:

“The authors combine results from several studies to assess the association between the number of hours worked per week and the risk of developing atrial fibrillation, the name for an irregular and often abnormally fast heart rate.

“This study reports an association between working 55 hours or more per week at one point in time and an increased risk of atrial fibrillation, when compared to working 35-40 hours a week.  There was little evidence to suggest those working between 41 and 54 hours a week were at increased risk of atrial fibrillation when compared to those working 35-40 hours a week.  Since the data in this study only gave a snapshot at one point in time of the participants’ working hours, it cannot say whether increasing someone’s working hours will increase their risk of atrial fibrillation and by how much.

“The results of this large, international study support the need for further research into working lifestyles and heart conditions.  However, there are some limitations.

“Participants were followed up for an average of 10 years, but we don’t know how they advanced or changed careers over time, nor how their weekly working hours changed during their lives.  We also don’t know how someone’s weekly hours were split over the week; for someone who reports working 48 hours a week, is that four 12-hour days, or six eight-hour days?  Furthermore, other lifestyle factors such as alcohol consumption and smoking status were not monitored over time.  Changes in these factors may also increase the risk of someone developing atrial fibrillation.”

Prof Sir Nilesh Samani, Medical Director, 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.  However, the observational nature of this research means these findings cannot confirm the cause of this relationship – it could be long working hours, it could be the type of work people do or it could be some other, unmeasured, factor.  More research is needed to understand and prove what’s behind this association.  Only then can we look at our recommendations.”

Dr Tim Chico, Reader in Cardiovascular Medicine / consultant cardiologist, University of Sheffield, said:

“Atrial fibrillation (often called AF) is the commonest abnormal heart rhythm and is very common; by the age of 80, 1 in 4 people have AF.  Most people with AF are not aware of it and it is often found coincidentally during medical checkups or before operations.  However, some people feel very unwell when they are in AF, and experience breathlessness, dizziness, or a sensation of their heart racing.

“This study finds that AF is more common in people who work long hours.  However, finding an ‘association’ between AF and long working hours does not prove that long working hours leads directly to AF as there may be other differences between people who work long hours (such as stress, or different sleep patterns) that are the real cause for the increased risk of AF.

“We know that a lot of AF is undiagnosed, and it is easily detected by having an ECG recording, so I would encourage anyone who feels their heart may be misbehaving to see their GP for this test.

“Most people who work long hours won’t have the luxury of being able to change their working pattern, and this study does not mean that they should worry that their work is affecting their health.  However, we already know that obesity, diabetes, high blood pressure and smoking all increase the risk of AF and so people can reduce their risk of AF by addressing these factors without needing to find another job!”

Prof. Carl Heneghan, Professor of Evidence-Based Medicine & Director of the Centre for Evidence-Based Medicine, University of Oxford, said:

“There are problems with the study on long working hours as a risk factor for Atrial Fibrillation that prevent drawing firm conclusions: assessment of working hours and lifestyle factors were only assessed once at the beginning of the study (it doesn’t take much to realise that working hours vary over time).  How atrial fibrillation was diagnosed was inconsistent between studies with many seemingly lacking gold standard criteria, and the absolute number of cases was small (varying between 13 and 449 in the included studies) meaning the element of a chance finding is much higher.  Furthermore, an association such as this is undermined by a lack of plausible mechanism explaining how the underlying effect might actually arise.”

* Paper: ‘Long working hours as a risk factor for atrial fibrillation: a multi-cohort study’ by Mika Kivimaki et al. will be published in the European Heart Journal at 00:05 UK time on Friday 14 July 2017, which is also when the embargo will lift. 

Editorial: ‘Do long working hours predispose to atrial fibrillation?’ by Bakhtawar K. Mahmoodi and Lucas V. Boersma will be published in the European Heart Journal at 00:05 UK time on Friday 14 July 2017, which is also when the embargo will lift. 

Declared interests

Dr Tim Chico: “I am a committee member and Treasurer of the British Atherosclerosis Society, a charity established in 1999 to promote UK atherosclerosis research.”

Prof. Carl Heneghan: “Carl Heneghan has received funding from the National Institute of Health Research for atrial fibrillation and self-monitoring of oral anticoagulation (one of the treatments for atrial fibrillation) and often works longer than 55 hours a week, but not always.”