Can chronotype affect the rest-activity circadian rhythm in shift workers?

Purpose: The working hours of shift workers, which are scheduled outside the normal daily social program, lead to a circadian desynchronization due to a temporary misalignment between working hours and physiological and behavioral functions, similar to what is observed in Jet-Lag. This condition leads to a worsening of sleep quality, a reduction in the ability to work during waking hours and alertness. The aim of the current study was to evaluate the effects of shift work on Rest-Activity circadian Rhythm (RAR) in a sample of nurses, taking into account their circadian typology. Methods: A total of 59 participants volunteered to be part of the study: 44 of them were night shift workers (Group 1) and other 15 were diurnal workers (Group 2). All 59 participants performed a continuous 7-day actigraphic monitoring to evaluate RAR and filled in the Morningness-Evenigness Questionnaire (MEQ) to detect the chronotype. Results: The single cosinor method revealed a statistically significant RAR in all participants. The population mean cosinor applied to Group 1 and Group 2 revealed the presence of a significant circadian rhythm in both groups. Only the Amplitude resulted significantly different between the two groups and lower in Group 1 compared to Group 2 (59.9±6.2 vs 90.6±14.26 a.c. in Group 1 and 2, respectively, p<0.001). Subsequently, we divided each group based on subject’s chronotype (M-types, N-types). The intra-group analysis of Group 1 revealed differences in Amplitude between M-types and N-types (68.5±12.48 vs 55.2±6.65 a.c. in M- and N-types, respectively, p<0.04). On the contrary, the intra-group analysis of Group 2 didn’t show differences in Amplitude of two chronotypes. The comparison between Group 1 and Group 2 for each chronotype showed an higher Amplitude for the Group 2 compared to the Group 1 (M-types: 95±26.88 vs 68.5±12.48 a.c. Group 2 vs Group 1, p<0.03; N-types: 86.5±23.5 vs 55.2±6.65 a.c. Group 2 vs Group 1, p<0.001). Conclusions: The RAR of night shift workers is disrupted with lower levels of Amplitude. In addition, the chronotype could affect this RAR alteration due to the presence of an higher Amplitude in M-types.