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Shiftwork increases the risk of abnormal heart rhythms, shows research in Occupational and Environmental Medicine. These changes may help to explain why shiftworkers are susceptible to heart disease.
Doctors measured changes in heartbeat and variations in heart rate in 49 employees working shifts, including nights, and 22 employees working normal day hours. All the employees were newly in post, and the measurements were taken between one week and two months after starting the new job and again after they had been in post for 12 months. The ages of the workers ranged from 18 to 55.
Abnormalities in heart rhythm were measured from changes in premature ventricular complexes (PVC), a term used when an irregular heartbeat occurs earlier than normal.
After one year, there were slight unfavourable changes in heart rate variability among both sets of workers. But the rate of PVC was significantly higher among the shiftworkers. Almost twice as many of them had developed this irregularity, the risk of which increased according to the number of night shifts worked. The results held true even after taking into account factors likely to skew the results, such as smoking habit, coffee and alcohol consumption, weight changes, age and sex and job stress.
The authors suggest that working at night may be a chronic stressor for the body. Other research has indicated that premature complexes occur in animals exposed to stress, and in people who are stressed and tired. They conclude that the increased frequency of early heartbeat patterns might be a factor in the higher risk of heart disease among shiftworkers.