Research article

Effects of a single dose of N-Acetyl-5-methoxytryptamine (Melatonin) and resistance exercise on the growth hormone/IGF-1 axis in young males and females

Erika Nassar¹ , Chris Mulligan² , Lem Taylor³ , Chad Kerksick⁴ , Melyn Galbreath¹ , Mike Greenwood¹ , Richard Kreider¹ and Darryn S Willoughby^1,5

¹  Department of Health, Human Performance, and Recreation, Baylor University, Box 97313, Waco, TX 76798, USA

²  Department of Nutrition and Food Science, Colorado State University, Fort Collins, CO 80523, USA

³  Department of Health, Leisure, and Exercise Science, University of West Florida, Pensacola, FL 32514, USA

⁴  Department of Health and Exercise Science, University of Oklahoma, Norman, OK 73019-6081, USA

⁵  Institute for Biomedical Studies, Baylor University, Waco, TX 76798, USA

author email corresponding author email

Journal of the International Society of Sports Nutrition 2007, 4:14doi:10.1186/1550-2783-4-14

Published:	23 October 2007

Abstract

Melatonin and resistance exercise alone have been shown to increase the levels of growth hormone (GH). The purpose of this study was to determine the effects of ingestion of a single dose of melatonin and heavy resistance exercise on serum GH, somatostatin (SST), and other hormones of the GH/insulin-like growth factor 1 (IGF-1) axis. Physically active males (n = 30) and females (n = 30) were randomly assigned to ingest either a melatonin supplement at 0.5 mg or 5.0 mg, or 1.0 mg of dextrose placebo. After a baseline blood sample, participants ingested the supplement and underwent blood sampling every 15 min for 60 min, at which point they underwent a single bout of resistance exercise with the leg press for 7 sets of 7 reps at 85% 1-RM. After exercise, participants provided additional blood samples every 15 min for a total of 120 min. Serum free GH, SST, IGF-1, IGFBP-1, and IGFBP-3 were determined with ELISA. Data were evaluated as the peak pre- and post-exercise values subtracted from baseline and the delta values analyzed with separate three-way ANOVA (p < 0.05). In males, when compared to placebo, 5.0 mg melatonin caused GH to increase (p = 0.017) and SST to decrease prior to exercise (p = 0.031), whereas both 0.5 and 5.0 mg melatonin were greater than placebo after exercise (p = 0.045) and less than placebo for SST. No significant differences occurred for IGF-1; however, males were shown to have higher levels of IGFBP-1 independent of supplementation (p = 0.004). The 5.0 mg melatonin dose resulted in higher IGFBP-3 in males (p = 0.017). In conclusion, for males 5.0 mg melatonin appears to increase serum GH while concomitantly lowering SST levels; however, when combined with resistance exercise both melatonin doses positively impacts GH levels in a manner not entirely dependent on SST.