Multiple Studies Report Variable Effects of L-Arginine

L-Arginine is a semi-essential amino acid widely marketed for its effects on Growth Hormone release and increase in muscle mass. Aside from its stimulatory effects on growth hormone, L-arginine is also said to be a potent vasodilator via its actions on nitric oxide. However, a recent study reports L-Arginine effects are more limited than previously thought.



Study on the effects of L-arginine

Objective: To evaluate the overall effects of L-arginine on serum insulin. IGF-1, Growth hormone, and cortisol with exercise. 

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Methodology: Blood samples were obtained from fifteen participants who were all well-trained runners. The samples were collected after randomly selecting runners to take either L-arginine or placebo. By timing the sample collection from the runners prior to intake of the supplement, immediately after the exercise, and 20 minutes after completion of the exercise. Each runner performed 5 km runs twice as a form of exercise. 

Results: Serum samples were reported to have a rise in growth hormone and cortisol levels in all runners with little difference in the quantity of the rise between the placebo and arginine supplemented groups. Although the rise in serum levels of insulin and IGF-1 was noted in both groups, there was no significant difference between the two groups. 

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The study’s researchers have concluded that L-arginine provides no significant induction of growth hormone, insulin, IGF-1, and cortisol secretion and therefore should not be routinely recommended as a supplement to increase levels of these hormones.

Other clinical trials on L-Arginine effects

A different clinical trial performed on fourteen marathon runners had contrasting results to this study. The fourteen runners were each randomly given either a placebo or arginine as a supplement starting two weeks prior to a marathon. Blood samples were collected from the runners on the marathon day both before and two hours after the 31-kilometer race. In this case, the researchers found a significant increase in levels of growth hormone in the runners who were supplemented with L-arginine in comparison to the runners who were not supplemented with the amino acid.
Another study examined the effects of L-arginine on seventeen participants who received 7 grams of arginine taken orally for one week. In this scenario, minimal differences in growth hormone and IGF-1 levels were observed between the two groups.

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However, the limited sample size of these clinical trials should also be taken into consideration prior to establishing that L-arginine provides no benefit for the increase in hormone secretions associated with muscle growth. A larger trial involving a variable group of participants examining the long-term effects of L-arginine on muscle growth may be more suitable to assess the true benefits of this semi-essential amino acid.

As the world of sports gets more and more competitive, the demand for supplements that enhances an athlete’s stamina and vigor is high. Thus many companies have stepped forward to provide numerous supplements with claims of a significantly improved impact on the runner’s physique and strength making the supplement manufacturing business a multibillion-dollar industry. Despite all of this, there have been very few studies that have studied the benefits or adverse effects of these supplements on the body.

A few clinical trials performed on limited sample sizes for a limited duration and with doubtable credibility have been conducted but they add little value to understanding the true effect of supplements due to their conflicting study results.

Each of the studies is limited in different aspects, some lack appropriate study duration while most of them are seriously flawed as they do not represent the population as a whole. A study’s results can be said to be significant when the participant size is large and random enough to represent the population as a whole, and if the study has been conducted over a number of years as opposed to a few days.


Hormonal response to L-arginine supplementation in physically active individuals

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