People who suffer from fatigue may benefit from taking a daily supplement of the amino acid l-ornithine, say Japanese Researchers.

Tomohiro Sugino and colleagues examined the effects of l-ornithine supplementation on physical fatigue in a study of 17 healthy volunteers. Volunteers were randomly assigned to take either l-ornithine (2000 mg/d for 7 days and 6000 mg/d for 1 day) or a placebo for 8 days. Each volunteer also had to take part in two fatigue-inducing two-hour sessions on an exercise bike.

Results showed that l-ornithine supplementation promoted lipid metabolism and activated the urea cycle. Furthermore, it reduced volunteers' subjective feeling of fatigue. However, the effect was only statistically significant in female volunteers.

The researchers concluded: “These results suggest that l-ornithine has an antifatigue effect by increasing the efficiency of energy consumption and promoting the excretion of ammonia. l-ornithine is a free amino acid and is not rich in meats or fish, so it is difficult to obtain amounts of l-ornithine from ordinary meals that would be sufficient to promote the antifatigue effect. We recommend l-ornithine intake as a nutritional supplement in cases of physical fatigue.”

Sugino T, Shirai T, Kajimoto Y, Kajimoto O. l-Ornithine supplementation attenuates physical fatigue in healthy volunteers by modulating lipid and amino acid metabolism. Nutrition Research. 2008;28:738-743.