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Arginine is sold both as an ingredient of pre-workouts and as a standalone supplement with the main goal of increasing nitric oxide (NO). This is supposed to cause vasodilation and thereby better blood and oxygen supply to the muscles. In this article, I will discuss the extent to which this reputation as a so-called “NO Booster” is justified. Additionally, I will also look at the potential added value of other effects of L-arginine.
Nitric Oxide (NO)
Nitric Oxide (NO) has multiple functions in the body. NO is the chemical formula for the molecule. This simple molecule plays a role in various important processes in different sciences such as psychology and neurology and was therefore elected “Molecule of the Year” in 1992. It also plays a crucial role in multiple biological processes.
It acts as a signaling molecule, or “intercellular signaling substance.” NO conveys information between cells.
It is a neurotransmitter in the central nervous system (brain and spinal cord). It transmits nerve impulses between nerve cells/neurons.
It is also a neurotransmitter in the autonomic nervous system (the part outside the central nervous system that controls unconscious processes). In this function, it relaxes smooth muscle tissues in, for example, the gastrointestinal tract and in the penis.
Read also the article: Arginine for a Better Erection?
By relaxing smooth muscle tissue, NO acts as a vasodilator. It dilates blood vessels, thus lowering blood pressure and playing a role in regulating blood flow to organs, including the skeletal muscles we train.
NO is an “Endothelium-derived relaxing factor” (EDRF)*. “Endothelium-derived” means that it is produced and released by endothelium, a covering layer of endothelial cells that line the inside of, among others, blood vessels and the heart. “Relaxing Factor” refers to its relaxing effect on the walls of blood vessels in smooth muscle tissue.
*Some sources mention NO as an example of an EDRF, while others consider it the EDRF itself. Research is still being conducted to determine if other EDRFs exist.
There are two ways in which the body produces NO.
NO Produced with the Help of Arginine
NO is produced in these cells from a reaction of the amino acid L-Arginine with oxygen and NADP+ (Nicotinamide adenine dinucleotide phosphate). NADP+ is a coenzyme necessary for the “biological activity of a protein.” The protein in this case that requires the assistance of NADP+ is the enzyme called nitric oxide synthase (NOS). This enzyme acts as a catalyst in the conversion of arginine into NO.
“Arginine Paradox”
The enhancing effect that arginine has via NOS is controversial.
The arginine paradox refers to the difference between, on the one
hand, the amount of arginine in the body and, on the other hand, the amount of NO that can be produced from it.
The paradox is that, despite large amounts of arginine in the body, the synthesis of NO is not unlimited. The reason for this is that the availability of NADP+ limits NO synthesis.
This means that providing additional arginine does not automatically lead to more NO production. The synthesis of NO only increases if the body has more NADP+ available to make use of the additional arginine.
Research has shown that the body can regulate the concentration of arginine in cells within wide limits. As a result, the concentration of arginine is usually not a limiting factor for the synthesis of NO.
What is L-Arginine?
Arginine is a non-essential amino acid that the body can produce itself. This amino acid was first isolated in 1886 by the Swiss chemist Ernst Schulze.
The body needs arginine for various physiological processes. These processes include the production of growth hormone, urea, and creatine. Growth hormone is involved in, among other things, tissue repair, muscle building, and fat burning. Urea is formed during the breakdown of proteins. Creatine plays a role in supplying energy to muscle cells.
Citrulline -NO or Arginine-Citrulline Pathway
There is another way to increase the production of arginine-derived NO. This is via the citrulline-NO or arginine-citrulline pathway. In this pathway, citrulline is converted back into arginine. This arginine is then used again for the production of NO.
Citrulline is an amino acid that the body can produce from glutamine and ornithine. The body uses citrulline, among other things, in the urea cycle. Here it plays a role in the excretion of ammonia, a waste product of protein breakdown.
Citrulline is present in, among other things, watermelon and nuts. It is also available as a dietary supplement. There is evidence that citrulline supplementation leads to higher levels of arginine and NO in the blood compared to arginine supplementation.
The increased levels of NO as a result of citrulline supplementation are also associated with a number of positive effects on physical performance.
Is Arginine Effective as NO Booster?
Research on the effectiveness of arginine supplementation as an NO booster has produced inconsistent results. Some studies show that arginine supplementation increases NO production and has positive effects on physical performance. Other studies find no or minimal effects.
The differences in results may be due to differences in study design, the health status of the participants, or the duration and dosage of supplementation. The effectiveness of arginine supplementation may also depend on whether the body has sufficient NADP+ available to convert arginine into NO.
Arginine or Citrulline?
Given the mixed results of studies on the effectiveness of arginine supplementation as an NO booster, some researchers advocate using citrulline instead of arginine. Citrulline supplementation increases arginine and NO levels in the blood more effectively than arginine supplementation.
In addition, citrulline supplementation is associated with positive effects on physical performance, such as increased strength and endurance, and reduced fatigue.
Therefore, if you want to increase NO levels and improve physical performance, citrulline supplementation may be a better option than arginine supplementation.
Summary
Arginine is a non-essential amino acid that the body can produce itself. It is a precursor of nitric oxide (NO), a molecule with various important functions in the body. NO acts as a signaling molecule, neurotransmitter, and endothelium-derived relaxing factor (EDRF). It plays a role in regulating blood flow, neurotransmission, and smooth muscle relaxation.
Arginine supplementation may increase NO levels and have positive effects on physical performance. However, research on the effectiveness of arginine supplementation has produced inconsistent results. Some studies show that arginine supplementation increases NO production and improves physical performance, while others find no or minimal effects.
Citrulline supplementation may be a better option than arginine supplementation for increasing NO levels and improving physical performance. Citrulline supplementation leads to higher levels of arginine and NO in the blood compared to arginine supplementation and is associated with positive effects on physical performance, such as increased strength and endurance, and reduced fatigue.
Therefore, if you want to increase NO levels and improve physical performance, citrulline supplementation may be a more effective strategy than arginine supplementation.
