Work start time and chronotype of indoor and outdoor daytime workers

Background and objective: Natural light exposure has important effects on the biological timing systems. One could suppose that this exposure might promote a better adjustment between biological rhythms and early working times among outdoor diurnal workers. The aim of this study was to compare the morningness/eveningness preferences and the relationship between actual and ideal timing to work on diurnal workers exposed to different light conditions. Methods: The study was conducted with two groups of workers (n=49) living in a rural area and exposed to similar social conditions. One group worked indoor (n=20, mean age 30.8 years (21-50); standard deviation=9.8), and the other group worked outdoor (n=29, mean age 30.8 years (17-50); standard deviation=10.0). The workers filled out a morningness-eveningness questionnaire (MEQ). A one-way ANOVA was carried out in order to compare MEQ scores between the two groups of workers. Results: As expected, Outdoor Environment Group (OEG) showed a higher average when compared to Indoor Environment Group (IEG), which means a trend to a morning preference (OEG: 58.4±7.9; IEG: 47.4±6.4), with a significant difference (F=26.22; p<0.001). According to the reported data related to working times, the OEG would like to postpone the working time by 31 minutes, while the IEG would postpone by 96 minutes their actual working time (F=7.71; p<0.01). Conclusions: The results of this study suggested that natural light exposure may promote better adjustment to early working hours.