Nassar, E., Mulligan, C., Taylor, L, Kerksick, C., Galbreath, M., Greenwood, M., Kreider, R., & Willoughby, D. S. (2007). 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. Journal of the International Society of Sports Nutrition, 4, 14.

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"Melatonin and resistance exercise alone have been shown to increase the levels of growth hormone". This study determined the effects of ingestion of a single dose of melatonin and heavy resistance exercise on serum growth hormone, somatostatin, and other hormones of the growth hormone/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 of 0.5 mg or 5.0 mg, or 1.0 mg of dextrose placebo. After a baseline blood sample, Ss ingested the supplement and underwent blood sampling every 15 minutes for 60 minutes, at which point they underwent a single bout of resistance exercise with the leg press for seven sets of seven repetitions at 85% 1-RM. After exercise, Ss provided additional blood samples every 15 minutes for a total of 120 minutes.

Compared to placebo, males who ingested 5.0 mg melatonin demonstrated a growth hormone increase and somatostatin decrease prior to exercise. After exercise, 0.5 and 5.0 mg melatonin groups were greater than placebo and less than placebo for somatostatin. No significant differences occurred for IGF-1; however, males were shown to have higher levels of IGFBP-1 independent of supplementation. The 5.0 mg melatonin dose resulted in higher IGFBP-3 in males.

Implication. A 5.0 mg melatonin supplementation increases serum growth hormone while concomitantly lowering somatostatin levels. When combined with resistance exercise, both melatonin doses positively impact growth hormone levels in a manner not entirely dependent on somatostatin.

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