Written by Greg Arnold, DC, CSCS. Citrulline supplementation during a cycling test significantly improved blood pressure, blood oxidation, and time to exhaustion by 13.9%, 8.9%, and 12.6% respectively compared to arginine or placebo.  

When athletes seek natural ways to improve their performance, a common focus is to increase levels of nitric oxide in their body because of its ability to dilate blood vessels and thereby improve muscle function (1). When the body makes nitric oxide, a necessary ingredient is the amino acid arginine (2) which has been shown to increase exercise performance (3).

But there is a “significant obstacle” to supplementing with arginine, as 40% is broken down in the intestines (4) and an additional 10-15% is broken down by the liver (5), leaving less than half of supplemented arginine available for use in the blood to make nitric oxide. As a result, finding a more efficient way to increase nitric oxide levels is warranted.

Now a new study (6) suggests another amino acid, L-Citrulline, may be a viable alternative to arginine to increase nitric oxide levels. L-Citrulline is a byproduct of nitric oxide production in the blood and is actually recycled into arginine (7). It is more stable than arginine, as it is not broken down in the intestines or the liver (8), allowing most of L-Citrulline to enter the blood (9).

The study involved 10 healthy adult men between the ages of 18 and 20. They took arginine (6 grams per day with 4.3 grams of maltodextrin), citrulline (6 grams per day with 4.3 grams of maltodextrin) or placebo (10.7 grams of maltodextrin) for 6 days. They then completed a cycling exercise during which they cycled at a pace of 70-90 repetitions per minute for 3 minutes at no resistance (0 Watts) and then increased by 30 Watts per minute until they reached their limit of tolerance.

The researchers found a significant benefit with citrulline supplementation compared to both arginine and placebo. In addition to having a significantly lower blood pressure after the 6 days of supplementation (118/85 mmHg) compared to arginine (121/86 mmHg) and placebo (122/87 mmHg) (p < 0.05), those in the citrulline group had a 13.9% higher oxygenation of the blood at the end of their exercise periods using a measurement called “tissue oxygenation index” (49% vs. 43% in the arginine group and 43% in the placebo group) (p < 0.05). This resulted in the citrulline group having an 8.9% greater time to exhaustion during the cycling test (670 seconds) compared to the arginine group (615 seconds) and a 12.6% greater time to exhaustion than the placebo group (595 seconds) (p < 0.05).

For the researchers, “the results of this study suggest that chronic supplementation with L-Citrulline might represent a practical, dietary intervention to reduce blood pressure and enhance oxidative metabolism and exercise performance in young healthy adults.”

Source: Bailey, Stephen J., et al. “L-citrulline supplementation improves O2 uptake kinetics and high-intensity exercise performance in humans.” Journal of Applied Physiology 119.4 (2015): 385-395.

8750-7587/15 Copyright

© 2015 the American Physiological Society

Posted October 6, 2015.

Greg Arnold is a Chiropractic Physician practicing in Hauppauge, NY.  You can contact Dr. Arnold directly by emailing him at PitchingDoc@msn.com or visiting his web site at www.PitchingDoc.com.

References:

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  2. Stamler JS, Meissner G. Physiology of nitric oxide in skeletal muscle. Physiol Rev 81: 209–237, 2001
  3. Schaefer A, Piquard F, Geny B, Doutreleau S, Lampert E, Mettauer B, Lonsdorfer J. L-Arginine reduces exercise-induced increase in plasma lactate and ammonia. Int J Sports Med 23: 403–407, 2002
  4. Castillo L, deRojas TC, Chapman TE, Vogt J, Burke JF, Tannenbaum SR, Young VR. Splanchnic metabolism of dietary arginine in relation to nitric oxide synthesis in normal adult man. Proc Natl Acad Sci USA 90: 193–197, 1993
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  6. Bailey SJ. L-Citrulline supplementation improves O2 uptake kinetics and high-intensity exercise performance in humans. J Appl Physiol (1985) 2015 Aug 15;119(4):385-95. doi: 10.1152/japplphysiol.00192.2014. Epub 2015 May 28
  7. Haines RJ, Pendleton LC, Eichler DC. Argininosuccinate synthase: at the center of arginine metabolism. Int J Biochem Mol Biol 2: 8–23, 2011
  8. van de Poll MC, Siroen MP, van Leeuwen PA, Soeters PB, Melis GC, Boelens PG, Deutz NE, Dejong CH. Interorgan amino acid exchange in humans: consequences for arginine and citrulline metabolism. Am J Clin Nutr 85: 167–172, 2007
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