Ornithine is an amino acid that is produced from arginine in the body, and can be converted back to arginine. Arginine and ornithine are often used together in supplement form to support exercise performance, including with the aim of stimulating growth hormone production. A double-blind study on experienced strength-trained athletes found that those supplementing arginine and ornithine had higher growth hormone levels after an exercise test compared with the placebo group.[25] This effect on growth hormone is thought to be due to conversion of ornithine to arginine.

Arginine and ornithine together in supplement form have also been found to increase lean body mass and total strength in men participating in a 5-week strength training programme[26]; and in another trial, ornithine on its own was found to directly improve energy levels and reduce physical fatigue after exercise, in this case a cycling test[27].

Also like arginine, ornithine may support collagen synthesis. A study on mice found that ornithine supplementation enhanced wound healing and collagen deposition.[28]



25. Zajac A et al. Arginine and ornithine supplementation increases growth hormone and insulin-like growth factor-1 serum levels after heavy-resistance exercise in strength-trained athletes. J Strength Cond Res. 2010 Apr;24(4):1082-90.

26. Elam RP et al. Effects of arginine and ornithine on strength, lean body mass and urinary hydroxyproline in adult males. J Sports Med Phys Fitness. 1989 Mar;29(1):52-6.

27. Sugino T et al. L-ornithine supplementation attenuates physical fatigue in healthy volunteers by modulating lipid and amino acid metabolism. Nutr Res. 2008 Nov;28(11):738-43.
28. Shi HP et al. Effect of supplemental ornithine on wound healing. J Surg Res. 2002 Aug;106(2):299-302.





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