The increased rate of heart disease and accidents associated with shift work could be because the body's circadian rhythms are programmed to slow down at night and increase during the day, regardless of whether the body is active or not.

In a study published in the 17 October Circulation, scientists at the University of Milan studied 22 male steel workers, who worked three types of shift, rotated weekly. The shifts included 06:00–14:00, 14:00–22:00 and 22:00–06:00. For each shift the workers were given two days to adjust, and then ECG recordings were monitored continuously over 24 hours. The researchers also conducted spectral analysis of heart rate variability, which provided normalized markers of sympathetic (LFnu) and vagal (HFnu) modulation of the sinoatrial node activity and of the sympathovagal balance (LF/HF). Dr Raffaello Furlan and his team found that regardless of work schedule, the sympathetic and vagal autonomic...

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