(Reuters Health) – People who typically work much more than 35 to 40 hours a week may be at heightened risk of developing atrial fibrillation, an irregular rapid heartbeat that can lead to strokes, heart failure and chronic fatigue, a recent study suggests.
For the study, researchers followed more than 85,000 working men and women without an atrial fibrillation diagnosis for a decade, starting when they were typically around 43 years old. During the study period, people who worked at least 55 hours a week were 40 percent more likely to develop atrial fibrillation than those who worked 35 to 40 hours.
“This study is important because it suggests a potential mechanism that could link long working hours to stroke,” said lead study author Dr. Mika Kivimaki of University College London in the UK.
To assess the connection between work hours and atrial fibrillation, Kivimaki and colleagues examined data on workers in the UK, Denmark, Sweden and Finland.
When participants joined the study between 1991 and 2004, about 63 percent of them worked a standard 35 to 40 hour workweek, while just 5.2 percent worked 55 hours or more.
Long working hours were associated with slightly higher rates of obesity, inactivity, smoking and alcohol use.
During the study, 1,061 people were diagnosed with atrial fibrillation, researchers report in the European Heart Journal. Only 10 percent of them had already been diagnosed with heart disease by the time atrial fibrillation was found.
“For me, this was perhaps the most surprising finding,” Kivimaki said by email. “Initially, I thought people who work long hours may have a greater risk of coronary heart disease, which then elevates atrial fibrillation risk. Our findings show that the association from long working hours with atrial fibrillation was more direct.”
In atrial fibrillation, electrical impulses in the upper chambers of the heart are chaotic, causing that part of the heart muscle to quiver rather than contracting normally. As a result, blood doesn’t move as well to the heart’s lower chambers. This can lead to the formation of blood clots, which can then travel through the arteries to the brain and cause a stroke.
Among people working a standard week, 12.4 out of every 1,000 developed atrial fibrillation, the study found.
But when people worked at least 55 hours, 17.6 out of every 1,000 got this diagnosis.
The study wasn’t a controlled experiment designed to prove that working too much directly causes atrial fibrillation.
Other limitations include the lack of data on the type of job people worked or whether they typically worked day or night shifts, the authors note. In addition, researchers only had data on work hours and lifestyle behaviors like diet, exercise, smoking and alcohol use from a single assessment done at the start of the study period.
People might have changed jobs, working hours or shifts during the study, Drs. Lucas Boersma and Bakhtawar Mahmoodi, of St. Antonius Hospital in Nieuwegein, The Netherlands, write in an accompanying editorial. Shifts in things like diet and exercise might also explain some of the connection between long work hours and atrial fibrillation.
“It is probably not the direct effect of working longer hours that causes atrial fibrillation to develop. Most likely it is in the balance of amount of work load and how much work load each individual is able to endure over the long term,” Boersma told Reuters Health by email.
“The type of work is also of great importance: stress level, physical labor, education and being equipped for the task at hand, working changing shifts, traveling through different time zones continuously, etc.,” Boersma added. “All of these may demand more than individual systems can take.”