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How Much Do You NO?
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Written by:
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Reviewed for medical accuracy by:
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Added to knowledge base:
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Rob Egbers
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Kestrson S., M.D.
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01/08/07
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UM Medical School
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One of the hottest athletic supplements available is
L-arginine, marketed as Nitric Oxide. You can buy it as a pure
supplement or as an additive in common mixtures such as BSN NO-Xplode,
Xyience NOX-CG3, or any protein supplement. This article will be a beneficial
read for anyone taking or considering an arginine supplement. Even if
you aren't thinking about taking L-arginine, look at the supplements that you
are currently taking and there is a good chance you will find it as an
ingredient.
The
Basics
L-arginine is an amino acid that is found in high concentrations in nuts,
seeds and raisins. It is used by the body for protein syntheses, wound
healing and removing urea and nitrogen waste from the body. More
recently, scientists discovered that L-arginine is the precursor for the gas
nitric oxide (NO) produced in the body via the following reaction:
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L-Arginine
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NADPH, O2
Nitric Oxide Synthase (enzyme)
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L-Citrulline
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+
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·N=O
(Nitric Oxide)
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This reaction occurs in neurons, in the immune system where
NO acts as a defense mechanism, and in cells which line the blood vessels of
your body (endothelial cells). As athletes, our primary concern is with
NO’s ability to dilate our arteries allowing more blood to flow to our
muscles, which is called vasodilation. Under normal conditions, NO is
released in blood vessels in response to an increased volume of blood trying
to get through the vessels. These NO molecules then diffuse from the
lining of blood vessels to the surrounding smooth muscle cells and allows
them to relax. The idea with supplementation is that by taking more
L-arginine your body will be able to produce more NO. This relaxation
allows more blood filled with protein, oxygen and nutrients to flow through
the arteries to your muscles, aiding in workout and recovery.
What
scientific data do we have to support these claims?
The human body is extremely complex and just because we can theorize how a
supplement may help us it doesn’t prove that you will be able to lift
more weight or gain more muscle mass. Experiments with actual people
need to be evaluated to determine the effectiveness of supplementation with
L-arginine.
So far, studies have shown contradictory evidence on the
effects of L-arginine supplementation. L-arginine supplementation has
been shown to increase blood flow in healthy individuals at rest [2,3] and in
individuals with certain diseases such as heart failure [1], diabetes,
smokers, high cholesterol and high blood pressure [13]. However,
research finds no increase in blood flow with arginine supplementation in
healthy individuals during exercise [2,3,4], even through NO production has
been shown to increase during exercise [5,6]. It has been postulated
that this is due to the multitude of other vasodilatory factors at work
during exercise such as potassium, hydrogen ions, adenine and prostaglandins
[4]. Also, and maybe more importantly, during exercise the production
of NO may not limited by the substrate arginine [14]. This means that
taking more L-arginine under exercise conditions wont increase the output of
NO.
On the other hand, L-arginine supplementation has been shown
to have beneficial effects beyond those related to vasodilation. Some
recent publications suggest L-arginine supplementation reduces plasma
lactate, ammonia [7,9,10] and blood glucose [8,9,10]. Build-up of
lactate and ammonia lead to fatigue during exercise. Increasing glucose
clearance means more energy will be available inside muscle cells to finish a
work out. It has been proposed that the increase in glucose clearance
results from an increase in glucose uptake by muscle cells by glucose
transporters rather than from vasodilation [8].
A current misconception associated with L-arginine is that it
causes an increase in growth hormone release. Intravenously
administered large quantities of arginine has been shown to increase growth
hormone secretion (via inhibition of somatostatin). Orally administered
arginine on the other hand has been shown not to increase growth hormone
secretion in well trained athletes [11,12]. Part of the problem with
orally administered arginine is palatability. Oral doses that do cause
a slight increase in growth hormone in secretion in athletes cause diarrhea
and stomach cramping. Growth hormone has anabolic effects to increase
amino acid uptake, protein synthesis, fat mobilization and maintenance of
blood glucose concentration.
How
safe is this product?
Systems in the human body do not operate in a vacuum. What you put in
to your body could affect more than just the one or two types of cells where
the effect is desired. People with herpes simplex virus should be aware
that arginine can stimulate virus growth. Also a theoretical interaction
exists with erectile dysfunction medications or nitroglycerine.
Headache, nausea, diarrhea and weakness have been reported if taken in
excess. Like with any other supplement you want to start, consult your
doctor before taking.
Is it
worthwhile to take an L-arginine supplement?
It still isn't clear weather or not L-arginine supplementation will give you
the increased blood flow you want to improve athletic performance. More
research needs to be done on the subject. However, research has shown
some other benefits of L-arginine supplementation. Based on the current
available information, you should really think twice before shelling out
large sums of money on this product.
If you decide to take this product you should know that peak levels of orally
administered arginine occur between 1-2 hours after ingestion. And
authors suggested 4-5g of orally administered arginine to decrease plasma
lactate and ammonia during exercise [7].
- Kanaya, Y., Nakamura, M., Kobayashi, N., Hiramori,
K. Effects of lower limb vasodilator reserve and exercise capacity
in patients with chronic heart failure. Heart 1999; 81:512-517.
- Hickner, R.C., Fisher J.S., Ehsani A.A., Kohrt
W.M. Role of nitric oxide in skeletal muscle blood flow at rest
and during dynamic exercise in humans. Am. J. Physio. 1997;
273:405-410.
- Wilson, J.R., Kapoor, S. Contribution of
endothelium –derived relaxing factor to exercise-induced
vasodilation in humans. Am. J. Physio. 1993; 75:2740-2744.
- Brett, S., Cockcroft, J., Mant, T., Ritter, J.,
Chowienczyk, P. Haemodynamic effects of inhibition of nitric oxide
synthase and of L-arginine at rest and during exercise. J.
Hypertension. 1998; 16:429-435.
- Persson, M.G., Wiklund, N.P., Gustafsson, L.E.
Endogenous nitric oxide in single exhalations and the change during exercise.
Am. Rev. Resp. Dis. 1993; 148:1210-1214.
- Bode-Boger S.M., Boger, R.H., Schroder E.P.,
Frohlich, J.C. Exercise increases systemic nitric oxide production
in men. J. Cardiovascular Risk. 1994; 1:173-178.
- Schaefer, A., Piquard, F., Geny, B., Doutreleau, S.,
Lampbert, E., Mettauer, B., Lonsdorfer, J. L-arginine reduces
exercise-induced increase in plasma lactate and ammonia.
- McConell, G.K., Kingwell, B.A. Does nitric
oxide regulate skeletal muscle glucose uptake during exercise? Am.
Coll. Sports Med. 2006; 34:36-41.
- McConell, G.K., Hunh N.N., Lee-Young, R.S., Canny,
B.J., Wadley, G.D. L-arginine infusion increases glucose clearance
during prolonged exercise in humans. Am. J. Physio. 2006;
290:60-66.
- Mendonca, J.R., Lancha, A.H. Jr, Curi, R. Effect
of chronic diet supplementation of ornithine, citrulline and
arginine. Med. & Sci. in Sports & Exercise. 1996;
28:82.
- Moore, T.A., Switzer, B.R., McMurray, R.G., Hall,
J.E. Growth hormone response to oral arginine
supplementation. Med. & Sci. in Sports & Exercise.
1998; 30:18.
- Chromiak, J.A., Antonio, J. Use of amino acids
as growth hormone-releasing agents by athletes.
- Wu, G., Meininger, C., Knabe, D., Baze, F., Rhoads,
J. Arginine nutrition in development, health and disease.
Curr. Op. Clin. Nutrition and Metabolic Care. 2000; 3:59-66.
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