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Definition: "An ergogenic aid is any substance or phenomenon that enhances performance "

11.05.2023

Why NO-boosters with a modest amount of arginine and citrulline can still be effective

Most NO-boosters contain hefty amounts of L-citrulline, but according to a small Japanese study, huge amounts of this amino acid are not necessary to have a performance-enhancing effect. If you combine L-arginine and L-citrulline, 2 grams could already be effective. Another Japanese study clarifies how.

Study
Researchers at the Japanese amino acid producer Kyowa Hakko Bio [kyowahakko-bio.co.jp] published a human study in 2017, in which they divided 45 healthy Japanese men into 4 groups.

One group of men received a placebo, the other 2 grams of L-arginine, another group of men received 2 grams of L-citrulline and finally there was another group of men who received 1 gram of L-arginine and 1 gram of L-citrulline.

The researchers then monitored the concentration of L-arginine in the men's blood for 4 hours.

Nitric Oxide [NO]
L-arginine is a precursor of nitric oxide [NO]. NO relaxes blood vessels, so that muscles receive more oxygen and glucose during intensive exercise and can more easily remove waste products. As a result, supplementation with NO boosters can improve sports performance.

A problem here is that the enzyme arginase quickly breaks down L-arginine in the body. This already happens in the intestine, when the body absorbs L-arginine, [Proc Natl Acad Sci U S A. 1993 Jan 1;90(1):193-7.] but also in the liver. [Am J Clin Nutr. 2007 Jan;85(1):167-72.]

An alternative to L-arginine supplementation is L-citrulline supplementation, an amino acid that breaks down less quickly and can be converted back into L-arginine. The chemical structure of both amino acids is similar, but L-citrulline jams the enzyme arginase. [Circ Res. 2008 Jan 4;102(1):95-102.]

The Japanese wondered what happens if you administer both amino acids. If L-citrulline inhibits arginase, the absorption of L-arginine in the intestines may increase. Co-supplementation could also result in a greater increase in NO concentration in the blood.

The Japanese did not look at the concentration of NO, which is rather complicated if you want do it it right. They did look at the concentration of L-arginine.

Results
Supplementation with L-citrulline resulted in a higher concentration of L-arginine in the blood than supplementation with L-arginine. That was to be expected. But supplementation with both L-citrulline and L-arginine resulted in an even higher L-arginine concentration.

The figure and table below describe the effect over a period of 4 hours after intake.

Athletes who want to experiment with the combination of L-citrulline and L-arginine will probably get the best results if they take their supplements an hour before they want to reach their maximum performance.

At this point, the concentration of L-arginine in the blood peaks - and probably also the activity of NO.

Source:
Biosci Biotechnol Biochem. 2017 Feb;81(2):372-5.

More:
Just over two grams of arginine-citrulline combi enough to make athletes faster and fitter 29.10.2019
Animal study | Better NO boosters contain a combination of L-arginine and L-citrulline 11.02.2015

Archives:
Boosting Nitric Oxide [NO]
Amino Acids
L-Citrulline
L-Arginine

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