Long working week 'may increase risk of irregular heartbeat'

Friday July 14 2017

"Long working days can cause heart problems, study says," The Guardian reports.

Researchers found people who work 55 or more hours a week had an increased risk of developing a type of irregular heartbeat known as atrial fibrillation, where the heart can beat very fast. 

Complications of atrial fibrillation include stroke and heart failure.

The researchers pooled data from eight studies across western Europe, including data from more than 85,000 adults.

Overall, they found people who worked the longest (55 hours or more) a week had about a 40% increased risk of developing atrial fibrillation over 10 years.

But only 1.2% of the whole group studied developed atrial fibrillation, so the actual baseline risk is very small. Even if your risk was increased by 40%, this is still only a 1.7% risk.

Many health and lifestyle factors could have contributed to the link – for example, people who worked longer hours may have been more likely to have unhealthier lifestyle habits. The studies may not have fully accounted for these.

The best way to reduce your risk of heart and vascular problems is to have a healthy, balanced diet, take regular exercise, and avoid smoking and drinking too much alcohol.

A healthy work-life balance is also important. Persistently working long hours can cause stress, which can in turn lead to problems with both your physical and mental health.

Read more about workplace health.

Where did the story come from?

The study was carried out by the Individual-Participant-Data Meta-analysis in Working Populations (IPD-Work) Consortium, comprised of researchers from extensive institutions worldwide.

Funding was provided by NordForsk, the Nordic Research Programme on Health and Welfare, the EU New OSH ERA research programme, the Finnish Work Environment Fund, the Swedish Research Council for Working Life and Social Research, the Danish National Research Centre for the Working Environment, and the UK Medical Research Council.

The study was published in the peer-reviewed European Heart Journal, and the article is free to read online.

The media coverage would have benefited from highlighting the very small overall risk of atrial fibrillation – estimated to be an increase from 1.2% to 1.7%.

The Sun's reporting was also inaccurate, stating that, "Working more than 50 hours a week 'increases your risk of heart failure and stroke by 40%'."

Working 55 hours, not 50, saw the increase in risk, and the research only looked at the development of atrial fibrillation, not subsequent health outcomes like heart failure and stroke.

What kind of research was this?

This collective analysis of data from several prospective cohort studies aimed to see whether working longer hours (over 55 hours a week) was linked to an increased risk of atrial fibrillation.

Atrial fibrillation (AF) is a completely irregular heart rhythm that's often also abnormally fast, and can cause strokes.

Some studies have suggested that stress and exhaustion can lead to AF, although the evidence isn't very strong.

The study aimed to look at this issue in a large population of people taking part in several cohort studies making up the IPD-Work project. This is a Europe-wide collaborative project looking at how working habits can impact on health.

What did the research involve?

The study analysed data from eight of the cohort studies in the IPD-Work Consortium that had data available on working hours and AF.

These were multi-purpose studies designed to examine health effects across a range of risk factors, including those related to the workplace.

The total sample for this study included 85,494 adults (65% women, 35% men) from the UK, Denmark, Sweden, and Finland who didn't have a diagnosis of AF at the start of the study between 1991 and 2004.

At the start of the study, researchers collected information on working hours.

People were grouped into:

  • part-time workers (less than 35 hours a week)
  • full-time workers with normal working hours (35-40 hours a week) – the control group
  • 41-48 hours a week – over standard working hours, but still in line with EU rules
  • 49-54 hours a week
  • 55 hours a week or more

AF was later identified through patient records, data on hospitalisations and deaths, and one of the cohorts had follow-up electrocardiograms (ECGs).

The researchers analysed and adjusted for extensive confounding factors. These included risk factors for AF assessed at the start of the study and during follow-up, such as respiratory infections, inflammatory conditions, diabetes, high blood pressure, stroke, and various forms of heart disease.

They also assessed various general confounders at baseline, including:

  • age
  • gender
  • socioeconomic status
  • body mass index
  • smoking history
  • alcohol use
  • physical activity levels

What were the basic results?

The average age of participants was 43.4 years at the start of the study. People were followed up for an average of 10 years. During this time, 1,061 were diagnosed with AF – a rate of 12.4 per 1,000, or around 1%.

The majority of study participants (62.5%; 53,468) worked standard working hours, with only 5.2% (4,484) working the longest hours of 55 hours or more each week.

When adjusting for age, sex and socioeconomic status, those who worked the longest hours had a 42% increased risk of developing AF compared with those who worked standard hours (hazard ratio [HR] 1.42, 95% confidence interval [CI] 1.13 to 1.80).

The general size of this association remained when adjusting for additional confounding factors like health, lifestyle and AF risk factors, including any previous history of heart disease or stroke (HR 1.36, 95% CI 1.05 to 1.76).

Other working hours patterns, such as working 41-48 hours a week, weren't associated with an increased risk compared with standard hours.

But although the eight pooled cohorts overall had an increased risk of AF, individually not a single one found a statistically significant increased risk of AF with long working hours.

How did the researchers interpret the results?

The researchers concluded: "Individuals who worked long hours were more likely to develop atrial fibrillation than those working standard." 

Conclusion

This study draws together data from a large group of people to investigate whether working hours could be linked to AF.

It found people who work 55 or more hours a week had an increased risk of developing an irregular heartbeat.

But before we jump to any conclusions, there are several important things to consider:

  • The number of people who developed AF during this study was small: only 1.24%. That's the absolute risk of AF. Even if working more than 55 hours a week does increase your risk of AF by around 40%, it would only be increasing it to something like 1.74% – which is still very small.
  • Only a small percentage of the cohort (5%) worked more than 55 hours a week. A further, much smaller, number of them will have developed AF. And analyses involving smaller samples are less accurate.
  • Although the eight pooled cohorts overall had an increased risk of AF, individually not a single one found a statistically significant increased risk of AF with long working hours.
  • Notable among these eight studies was the single Whitehall study, which took ECGs from the participants during follow-up and made the greatest adjustment for AF risk factors, so the results are likely to be more accurate. This study found no significant link with long working hours. Other studies were more variable in how they assessed AF, which may lead to an inaccurate representation of cases.
  • The number of working hours was only assessed at the start of the study and may have changed over time.
  • People who worked the longest hours were more likely to have unhealthier lifestyle habits, such as being obese, smoking, drinking too much alcohol, and getting less exercise. Even after adjusting for these factors, it's still difficult to prove that the working hours have directly and independently led to AF.

Although these findings on working hours are interesting, people shouldn't be overly alarmed. There are far more well-established lifestyle risk factors for heart disease, such as smoking, alcohol, diet, and activity.

Nevertheless, it's important to get a good work-life balance. Regularly working long hours could cause you physical and mental stress.

Read more about coping with stress at work.

Analysis by Bazian
Edited by NHS Choices