The daily dose of 2000 mg reduced symptoms of fatigue in 17 healthy volunteers taking part in the randomised, double-blind, placebo-controlled, two-way crossover study.
According to the Japanese researchers, it is difficult to consume the necessary active doses from food sources, such as meat and fish.
“We recommend l-ornithine intake as a nutritional supplement in cases of physical fatigue,” wrote lead author Tomohiro Sugino in the journal Nutrition Research.
Supplements of l-ornithine, often used in combination with arginine, are already available commercially, and are popular in the sports nutrition sector. The rapidly-growing sector is estimated to be about $6 billion this year and will be $22.8 billion by 2013 in the US, according to the Nutrition Business Journal.
A report last year from 3A Business Consulting indicated that sports nutrition market in Europe is set to surpass the €4bn mark by 2010 and is outstripping growth in North America. The total market on protein ingredients for sports nutrition in 2007 is estimated to represent a volume of approximately 17,000 tonnes and growing to approximately 20,000 tonnes in 2010.
The researchers, from Soiken Inc., Wakayama Medical University, and Osaka City University Graduate School of Medicine, recruited the volunteers and randomly assigned them to receive either daily ornithine supplements (2000 mg for seven days and 6000 mg for one day as l-ornithine hydrochloride, Kyowa Hakko) or placebo (crystalline cellulose). Kyowa Hakko funded the study.
The volunteers underwent fatigue-inducing physical tasks on an exercise bike for two hours on two occasions.
Supplementation with the amino acid was associated with improved lipid metabolism. In addition, the amino acid was linked to an activated urea cycle, said the researchers.
“L-ornithine is one of the products of the action of the enzyme arginase on l-arginine, creating urea. Therefore, l-ornithine is a central part of the urea cycle, which allows for the disposal of excess nitrogen,” they explained. “Therefore, l-ornithine is considered to inhibit the increase in blood ammonia level caused by physical load.”
Only the female participants experienced improvements in the ‘fatigue feeling’, said the researchers, compared to females in the placebo group.
“The role of l-ornithine has not been reported, except with regard to the urea cycle. In this study, it was suggested that l-ornithine promoted lipid metabolism, improved energy production, and attenuated fatigue,” wrote Sugino and his co-workers.
“To avoid long-term fatigue, it is important to develop effective strategies that attenuate fatigue; l-ornithine use may prevent the unfavorable consequences of accumulated physical fatigue,” they concluded.
Source: Nutrition ResearchNovember 2008, Volume 28, Issue 11, Pages 738-743“l-Ornithine supplementation attenuates physical fatigue in healthy volunteers by modulating lipid and amino acid metabolism”Authors: T. Sugino, T. Shirai, Y. Kajimoto, O. Kajimoto