Is social jetlag similar to travel-induced jetlag? Results of a validation study

Social jetlag (SJL) is defined as the misalignment between the biological clocks and the social clock imposed by work and social constraints. In order to accomplish the workdays duties, people tend to not respect the internally sleep-wake cycle during the week, often using alarm clock to wake-up, which would lead to a chronic form of travel-induced jetlag. This circadian misalignment has been found to be associated with increased health risk and health-impairing behaviors. In this cross-sectional study, we aimed to explore whether the SJL is a valid concept for the travel-induced jetlag symptoms, as well as what is the cutoff point with best parameters for defining the presence of SJL, in a sample of undergraduate students of a university in Southern Brazil. We assessed SJL by the Munich ChronoType Questionnaire (MCTQ) and defined the concept as the difference between the midsleep point on free days and the midsleep point on classes days. The gold standard was defined as having at least one travel-induced jetlag symptom (fatigue, sleepiness or difficulty concentrating). Relative SJL, sensitivity and specificity were calculated for different cutoff points, plotted on ROC curves. A total of 452 students with complete sleep information were included in the analysis. The relative SJL mean was 2 h 23 min (SD = 1 h 24 min; range -3 h to 7 h 58 min) and 63.7% of the students had ≥2 h of relative SJL. All the tested cutoff points of the instrument had low sensitivity and specificity values, covering a small area under the ROC curve (0.487). The best parameters were for the cutoff point ≥2 h, with 63.4% sensitivity and 35.9% specificity. SJL did not revealed to be a valid concept for the studied sample comparing it to travel-induced jetlag symptomatology. One possible explanation for the lack of validity of our results regards the fact that SJL may not have the same apparent wide-term effects as the travel-induced jetlag. Then, the symptoms of SJL do not well represent the symptoms of travel-induced jetlag.