Abstract
Abstract Introduction Timing of the human sleep-wake cycle is determined by social constraints, biological processes (sleep homeostasis and circadian rhythmicity) and environmental factors, particularly natural and electrical light exposure. However the effect of environmental factors, especially duration of sun exposure, on circadian rhythmicity remains unknown. We aimed to study the relationship between duration of sun exposure and chronotype among medical students. Methods Eighty-six GW medical students (62 F [71%], 24 M [29%]; ages 21-33 y [mean 24.4 y]) completed the Munich Chronotype Questionnaire (MCTQ). Mid points, the middle of the participants reported bedtime and wake time on workdays, were used to determine chronotype. Two independent groups based on the mean split (mean = 45) of the distribution of minutes of sun exposure were created: 45 minutes or more (n=31) vs less than 45 minutes (n = 55) of sun exposure. Independent samples t-test was performed to compare the measured midpoint with the following pairs of groups of reported work day sunlight exposure (in minutes): less than 45 min (n = 55) versus 45 min or more (n = 31). Results In the total sample (n = 86), no significant association between duration of sun exposure and midpoints was found using Pearson correlation. However, medical students with reported sun exposure of greater than or equal to 45 minutes a day had a significantly earlier chronotype compared to students reporting a sun exposure of less than 45 minutes a day [mid point 2.196 (SD 0.085) versus a mid point 3.386 (SD 1.084); t(69) = 2.021; p = .047]. Conclusion We found that, in GW medical students, greater amounts of sun exposure during the day was advancing the circadian rhythm. This may have implications on sleep duration and quality. Support NA
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