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Melatonin before cardio raises growth hormone release

Looking for a new way to speed up fat loss We found one that might work, in an article published ten years ago in the European Journal of Endocrinology. Then again, it might not work. In the article researchers from the British St Thomas’ Hospital describe how they raised growth hormone release after a cardio session by giving test subjects melatonin [structural formula shown below]. Maybe you haven’t noticed, but melatonin is on sale everywhere again.


Melatonin is a sleep hormone. Your brain makes it when it starts to get dark. It makes you feel sleepy, and helps you to fall asleep – and it probably also triggers the manufacture of messenger hormones and growth hormones in your brain. At night your production of growth hormone and testosterone rises. Scientists think that melatonin is involved in the mechanism that triggers this process. In tests where subjects took melatonin at night their growth hormone levels rose slightly. [Clin Endocrinol (Oxf). 1993 Aug;39(2):193-9.]

After physical exertion the growth hormone levels rose too. This response contributes to the slimming and muscle-building effects of training. That’s why sports scientists have spent years studying techniques to increase the growth hormone peak. So the Brits wondered whether giving athletes melatonin before they got on their bikes or pulled on their Nikes would have the same effect.

The Brits took seven healthy and active twenty-year-old students and gave them five mg of melatonin or a placebo early in the afternoon. An hour later the subjects cycled for eight minutes at seventy percent of their VO2max. That's a level at which it starts to be impossible to keep up a conversation.

The graph below shows the effect of the session on growth hormone release. The curve with the black blocks represents the students that had taken melatonin.

The concentration of the binding protein IGFBP-1 rose in the students that had taken the supplement. See below.

IGFBP-1 neutralises IGF-1, the growth factor that is released by growth hormone.

Fundamental research suggests that growth hormone itself induces muscles to burn more fat. But the muscle-building effect of growth hormone is thought to be mainly due to IGF-1. If that’s the case, ‘upping’ the effect of power training with melatonin is perhaps not such a good idea, but fat burning cardio sessions are a different story.

Melatonin probably doesn’t work in the evening. If you take it in the evening it’s likely to make you too sleepy to train.


The researchers think that melatonin gets its effect from the hormone GHRH – a messenger hormone from the hypothalamus that triggers the pituitary to make more GH. GHRH is released during physical exertion. You can increase the manufacture of GHRH while exercising through central alpha-1 and alpha-2 adrenergic stimulation, the Brits write. This is the same mechanism as found in mild and relatively harmless stimulants like caffeine. [Structural formula shown above.]

So how about putting melatonin and caffeine together in a cardio-stacker?

Eur J Endocrinol. 1999 Jul;141(1):22-6.

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