Does Resting for Two Consecutive Days Enable Complete Recovery From Night Work?

T he economic change, particularly the development of information and communication technology, has created the 24-h society where work can be done at any time, any place, and any shift, with night work becoming more common.1 Although the biological mechanism by which shift work increases the risk of cardiovascular disease has not been fully elucidated, there is evidence of a causal relationship between shift work and cardiovascular disease.2 Poor sleep and incomplete recovery from shift work can be a common pathway to cardiovascular disease; therefore, the scheduling of shift work to include a better distribution of free time may be a practical strategy to prevent the increased risk of cardiovascular disease that is associated with shift workers.1 Lo et al. conducted a study3 involving nurses and found that the recovery of daytime blood pressure during the off-duty period following the night shift was incomplete, and that the daytime blood pressure on the off-duty day was as high as that observed on work days. Therefore, the authors suggested that employees receive two consecutive off-duty days following a night shift. In their study,3 other possible confounding factors that could affect blood pressure or cardiovascular function, such as environmental work conditions, psychological and physical work load were controlled by restricting subjects who worked in the same occupational environment and did the same work. The individual characteristics and genetic effects were also controlled by self-control comparison of the blood pressure measured using an ambulatory blood pressure monitor (ABPM) for 48 h. Furthermore, restricting subjects to nurses who were unmarried and not caring for children may avoid the possible effect of the subjects’ extra burden at home, thereby allowing an accurate analysis of changes in daytime blood pressure following a night shift. However, further evidence is required to justify implementing a scheduling policy of at least two consecutive rest days following a night shift to decrease the risk of cardiovascular disease. For example, it is necessary to determine whether increased daytime blood pressure during off-duty days and increased