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Serum melatonin concentrations at baseline and after each shift during the melatonin arm (n = 25). Levels increased significantly over the series of shifts (P = 0.01 overall) and were higher after shift 3 than shift 2 (P = 0.016). Melatonin levels were not detectable at baseline in any participant. Box and whisker plots show median, interquartile, and full range with individual data points overlaid (n = 25).
