The amino acid L-citrulline – which Kyowa Hakko manufactures in the US in Cape Girardeau, MO using a proprietary fermentation process – is said to play an important role in nitric oxide (NO) metabolism and regulation. L-Citrulline is converted to L-Arginine in the body to support L-Arginine and NO levels. Increased production of NO promotes vascular dilation which improves oxygen and blood circulation throughout the body.
New data published in the Journal of the International Society of Sports Nutrition indicatedthat daily L-citrulline intake for seven days boosted L-citrulline and L-arginine levels and enhanced performance in a time trial.
Researchers from Kyowa Hakko and Kitasato University also report significant improvements in the feelings of muscle fatigue, and concentration, right after the time trial for people consuming L-citrulline.
Danielle Citrolo, Pharm.D, Technical Services Manager for Kyowa Hakko USA told NutraIngredients-USA: "In this study an increased arginine level from oral supplementation with L-citrulline showed a reduction in completion time by 1.5% a valuable decrease for those trained athletes that are participating in long distance cycling exercise. Not only did it improve performance, but the subjects reported feeling less muscle fatigue and an improved concentration using L-citrulline."
The researchers recruited 22 trained men to participate in their double-blind randomized placebo-controlled 2-way crossover study. The men were randomly assigned to receive either 2.4 grams per day of L-citrulline or placebo for eight days. On the eighth day, the men performed a 4 km time trial one hour after the final dose.
Results showed that, compared with placebo, men taking the L-citrulline supplements finished the time trial an average of 9 seconds faster.
In addition, power output was found to be 2% greater in the L- citrulline group, but there were no significant differences in VO2 response between the groups.
Finally, subjective feelings of muscle fatigue and concentration were also significantly improved immediately after exercise for men taking the L-citrulline supplements, compared with the placebo group.
“The improved time trial performance after supplementation with L-citrulline was the consequence of significantly greater PO for the same VO2,” wrote the researchers. “Interestingly, there was a significant correlation between plasma NOx and PO/VO2 after supplementation with L-citrulline but placebo had no correlation. This finding suggests that the effects of L-citrulline on PO/VO2 may have been related to improved plasma NO availability, which in turn may have enhanced sport performance.
“In sports nutrition, NO-related products are attracting a lot of attention for their ergogenic effects. Many applied studies in humans report that NO improves sports performance. This is because NO is a potential modulator of blood flow, muscle energy metabolism, and mitochondrial respiration during exercise.”
Source: Journal of the International Society of Sports Nutrition
2016, 13:6, doi: 10.1186/s12970-016-0117-z
“Oral L-citrulline supplementation enhances cycling time trial performance in healthy trained men: Double-blind randomized placebo-controlled 2-way crossover study”
Authors: T. Suzuki, M. Morita, Y. Kobayashi, A. Kamimura