The role of amino acids in male sexual health and fertility

Oxidative stress accounts for 30-80% of male infertility cases. It is known that appropriate combinations of antioxidants can be useful in suppressing the harmful effects of free radicals, and amino acids such as L-arginine, L-citrulline and L-carnitine play a role in the supportive therapy of erectile dysfunction, and at the same time play a role in male fertility.

L-arginine

L-arginine is a conditionally essential amino acid that has numerous positive effects, primarily on endothelial function, sports performance, insulin resistance and erectile function. Since it serves as a natural precursor of nitric oxide (English Nitrogen Oxide, NO), L-arginine is a frequently used substance in the therapy of erectile dysfunction.Different types of meat (turkey, chicken, veal, beef), dairy products, legumes (soy, peanuts, chickpeas), seeds (pumpkin seeds, sesame, pine nuts) and nuts (almonds, walnuts) naturally contain arginine.

Erection is a neurovascular event in which nitric oxide metabolism plays an important role. Reduced bioactivity of nitric oxide is noted in men with erectile dysfunction.

Since L-arginine is a natural precursor of NO, its good bioavailability has a positive effect on the production of NO itself. L-arginine is the most commonly used natural substance for sexual problems in men.

A 2017 study by Mozaffari-Khosravi H. et al.included 80 patients with type 2 diabetes and mild to moderate erectile dysfunction (number of points from 15 to 25 collected by the International Erectile Function Index Questionnaire (English International Index of Erectile Function, IIEF). Subjects were randomized to receive either a placebo or 5 g of L-arginine for four weeks. The research results showed that the daily application of 5 g of L-arginine for four weeks in men with type 2 diabetes and mild to moderate erectile dysfunction improves numerous parameters such as erectile function, sexual satisfaction and desire, sexual satisfaction, marital satisfaction and testosterone levels.

L-citrulline

L-citrulline is a conditionally essential amino acid present in the body, and it is a powerful endogenous precursor of L-arginine, which is a substrate for nitric oxide synthase (English Nitric Oxide Synthase, NOS). NOS catalyzes a complex enzymatic reaction that leads to the formation of NO from L-arginine and oxygen and generates L-citrulline as a byproduct.

L-citrulline is efficiently recycled through the L-citrulline NO cycle to L-arginine and plays an important role in NO metabolism and regulation. The advantage of L-citrulline is that, as a precursor, it more efficiently provides the necessary amounts of L-arginine and is not metabolized by the intestinal microbiota.

The best dietary source of L-citrulline is watermelon. Legumes, meat and nuts also contain this amino acid. Supplementation with L-citrulline has numerous beneficial effects, such as stimulating the elasticity of arteries, improving erectile function, memory, and physical and sports performance.

In studies that studied the effect of L-citrulline on erectile dysfunction, it was often used in combination with L-arginine. L-arginine and L-citrulline concentrations are decreased in men with severe erectile dysfunction.

The advantage of oral administration of the combination of L-citrulline and L-arginine compared to monosubstance L-arginine or L-citrulline

In a 2017 study by Suzuki and colleagues, the influence of the combination of 1 g of L-citrulline and 1 g of L-arginine on the level of L-arginine in the plasma was shown. The effect of this combination was compared with the use of 2 g of L-arginine or 2 g of L-citrulline as monosubstances. 45 men aged 20-49 participated in a double-blind, randomized, clinically controlled study. They were randomized into four groups that received placebo (starch), L-citrulline (2 g), L-arginine (2 g) or a combination of L-arginine and L-citrulline (1 g+1 g). The subjects took the preparation daily after breakfast for seven days.

The results of the research indicated the superiority of the combination of L-arginine and L-citrulline, since the highest level of L-arginine in the plasma was achieved after 30 minutes and after 1 hour, which is shown in Figure 2.

The authors of the study conclude that L-citrulline acts as an inhibitor of arginase and a precursor of L-arginine, and as a result of this mechanism of action, increase of L-arginine in plasma due to the synergistic action of L-arginine and L-citrulline.

L-carnitine

L-carnitine is a substance that is formed from the essential amino acids lysine and methionine, and is most often defined as a "substance similar to amino acids". The concentration of L-carnitine in the seminal fluid plays an important role in maintaining male fertility.Research shows that the use of L-carnitine in men can significantly improve the number and motility of sperm.

Our body produces L-carnitine independently, but it is estimated that the biosynthesis of L-carnitine meets 25% of the body's needs. The other 75% is ingested through food, mainly through meat, and we also find it in fish, wheat (very little), asparagus, avocado and peanut butter.

In a meta-analysis, the use of L-carnitine and L-acetyl-carnitine was observed in comparison with placebo, and a significant increase in the number of pregnancies and total sperm motility was observed in the group that received L-carnitine. No significant difference was found in sperm concentration and seminal fluid volume.

In conclusion, the use of L-carnitine can be an effective measure to help achieve pregnancy and improve the kinetic characteristics of sperm in men with infertility problems..

Author: Prof. Dr.Sc. Darija Vranešić Bender, clinical nutritionist

Literature:

1. Mozaffari-Khosravi H, Fallahi M, Afkhami-Ardekani.Effect of Oral Supplementation of L-arginine on Sexual Function in Men with Type 2 Diabetes: A Double-blind Clinical Trial. JNFS 2017; 2 (2): 165-172.

2. Suzuki T, Morita M, Hayashi T, Kamimura A. The effects on plasma L-arginine levels of combined oral L-citrulline and L-arginine supplementation in healthy males. Biosci Biotechnol Biochem. 2017;81(2):372-375.