A Pre-exercise Dose Of Melatonin Can Alter Blood Glucose Levels During Exercise.

Abstract

Melatonin is a pineal hormone championed by many researchers as a way to alleviate diabetes as well as the causes and symptoms of metabolic syndrome such as obesity, dyslipidemia, hyperglycemia, and insulin resistance (Recent Pat Endocr Metab Immune Drug Discov 2013, 7:11-25; Mol Cell Endocrinol. 2012 Feb 26,;349(2):128-37). Data concerning exogenous melatonin’s influence on fuel utilization during rest in humans, however, have been equivocal, showing melatonin to either increase glucose removal, or decrease glucose usage. In addition, changes in blood glucose with exogenous melatonin, during exercise have not been reported. PURPOSE: This study compared blood glucose levels during a 30 min graded exercise while on either 6 mg melatonin (M) or placebo (P, 50 mg methylcellulose). METHODS: Participants (4 women, 8 men, college students 21-29 years) performed stages 1-5 of the Naughton graded exercise protocol for 30 min (6 min stages). Each exercise was performed twice (1x M, 1x P) at the same time of day with 48 h separating each exercise. Both M and P were ingested 30 min prior to performing the exercise. Just prior to starting the exercise and at the end of each 6 min stage, blood glucose (BG), heart rate (HR), and blood pressure (BP) were obtained. RESULTS: Two-way repeated measures ANOVA for BG showed significant main effects for M vs. P (p = 0.014), and for Time (p <0.001). The interaction between M, P, and time was not statistically different (p = 0.503). Post-hoc Bonferroni t-tests showed that the majority of difference in BG between M and P were at the end of stage 1 (5.66±0.93 vs. 4.94±0.46) and stage 2 (5.30±0.47 vs. 4.90±0.60). Analysis of HR and BP showed significant increases with time, but no differences between M and P. CONCLUSIONS: Ingestion of melatonin 30 min prior to a low intensity aerobic exercise can increase BG levels. This suggests that if exercise is being used to combat metabolic syndrome, one should be careful about following the recommendation of using melatonin as an additional treatment modality for metabolic syndrome.