Seasonal Variations in Melatonin May Modulate Glycemic Response to Exercise

After a 30-min. standardized bicycle exercise at two times of day in 5 mo. of the year, 62 subjects showed a yearly variation in their glycemic response that was about 5 months out of phase with the peak levels in the light sensitive hormone melatonin, suggesting a reciprocal relationship between melatonin and glucose utilization.