Does working too much cause abnormal heart rhythms?
Working long hours has been associated with an increased risk of atrial fibrillation, new research has suggested. But how much are you risking your health by working overtime? Lucy Trelfa looks behind the headlines.
Previous research has linked working very long hours to negative effects on your health. Now a new study has suggested that it could increase your risk of heart rhythm problems.
Atrial fibrillation (AF) is the most common abnormal heart rhythm and is caused when the electrical messages that control the heart’s pumping action are sent out in an irregular, uncoordinated way. This can be felt as an irregular and sometimes fast heartbeat, and is a major cause of stroke.
Ten groups of scientists from across Europe combined their findings to conduct a large-scale study on long working hours and incidence of AF. Two studies were not included due to the low number of participants who worked long hours, and lack of AF in the follow up. In total, 85,495 working men and women were included from eight of the studies, who were followed up after an average of 10 years to check for AF.
At the start of each study, participants were asked about their cardiovascular health and lifestyle choices, such as smoking, physical activity and alcohol consumption. The scientists also took into consideration the age, sex and socioeconomic status of the participants. All of these factors could influence how likely somebody is to be diagnosed with AF.
Those working the longest hours were found to be more obese, more physically inactive, smoked more and consumed more alcohol
The researchers classified more than 55 hours per week as long working hours, and 35-40 hours per week as standard working hours. Out of the 85,495 participants, 5.2 per cent of participants worked long working hours, whilst 62.5 per cent worked standard hours. (The remainder worked less than 35 hours.)
At the end of the study period, the researchers analysed lifestyle and how many people had been diagnosed with AF. Those working the longest hours were found to be more obese, more physically inactive, smoked more and consumed more alcohol compared to those working standard hours. After taking these factors into account, they found that employees working 55 hours or more were 40 per cent more likely to develop AF than those working standard hours. Importantly, 9 out of 10 of new cases of AF occurred amongst people who had no cardiovascular disease recorded at the beginning of the study. In addition, they found the association was not due to lifestyle, socioeconomic factors or common risk factors for AF. This suggests that the increased risk of AF is down to the effect of working 55 hours or more a week.
How good is the research?
The study was large, looking at 85,295 working men and women across the UK, Finland, Denmark and Sweden. They also took into consideration factors which may influence the likelihood of being diagnosed with AF.
It is important to stress that the researchers found an association between working long hours and AF, rather than cause and effect. Additionally, working hours and lifestyle factors were only measured at the start of the study, meaning that any changes in working hours or lifestyle throughout the duration of the study were not taken into consideration. As a result of the lack of long-term, repeat measurements, the findings could over or underestimate the true effect on risk of AF. The researchers also did not take into consideration the type of work performed by each person in the study – some participants may have experienced more work-related stress than others.
It is important to stress that the researchers found an association, rather than cause and effect
Due to the research combining eight individual studies into one analysis, there were also differences in how AF was diagnosed in the follow up. For instance, some studies used electrocardiogram (ECG) analysis – the gold standard to detect problems in heart rhythm, whilst other studies were only able to access hospital admissions, death certificates or payments for drugs for the treatment of AF. This could have led to inconsistencies.
The BHF view
Professor Sir Nilesh Samani, Medical Director at the British Heart Foundation, said: “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.”
How was this story reported in the media?
The study was widely covered in the national press, including the Guardian, the Daily Mail, the Sun, the Telegraph and the Scotsman.
The media coverage was mostly accurate, but the Daily Mail and The Sun both failed to mention the main limitations of the study, such as the lack of repeated measures of working hours and lifestyle factors throughout the duration of the study.
More research is needed to understand and prove what’s behind this association
The Sun also misquoted the findings of the study in the headline of the article, stating that ‘working more than 50 hours a week’ increases risk of AF – long working hours were defined by the scientists as 55 hours or more per week (as was correctly reported in the main body of the article). The headline also said “Overtime IS killing you” – which we don’t know to be the case, as the study didn’t look at death rates. Atrial fibrillation is not usually life-threatening, although it can increase the risk of stroke, which can be life-threatening.
The Sun also got the rate of AF slightly wrong stating that ‘for every 1,000 participants, more than five cases of AF occurred among those working long hours’. The study actually found that AF affected both groups of workers - an average of 12.4 per 1000 in the standard working hours, and 17.6 people per 1000 amongst those working 55 hours or more. Presumably they intended to say that more than five additional cases of AF per 1,000 occurred in those working long hours.