Get Your Personalized Supplement StackSupplement Stack Quiz

Citrulline

Also known as: L-Citrulline, Stimol (Brand Name), citrulline malate

Overview

Citrulline is one of the three dietary amino acids in the urea cycle (the other two are L-arginine and L-ornithine). Taking citrulline increases plasma levels of arginine and improves the ammonia recycling process and nitric oxide metabolism. Consequently, citrulline may be useful in situations in which nitric oxide is relevant, such as athletic performance, vascular health, and erectile dysfunction. There are very few foods that have useful amounts of citrulline, but watermelon is a notable exception. The two most common forms of citrulline are L-citrulline and citrulline malate.

Benefits

Citrulline supplementation increases the body’s arginine levels. Because arginine is the main substrate for the synthesis of nitric oxide, citrulline ingestion can indirectly increase nitric oxide production. In turn, given the role of nitric oxide in vasodilation, mitochondrial respiration, calcium handling, and glucose uptake, greater amounts of nitric oxide can theoretically improve circulatory health and muscle function and reduce fatigue.

How it works

There is limited evidence that citrulline supplementation can reduce ratings of perceived exertion, decrease muscle soreness, and increase power output and total repetitions performed in resistance training. A considerable amount of research suggests that supplementation with citrulline mildly reduces blood pressure. More research is needed on citrulline’s potential effects for erectile dysfunction, but a small amount of research suggests a beneficial effect.

Side effects

To supplement L-citrulline for circulatory health or to alleviate erectile dysfunction, take 2,000 mg of citrulline, three times a day with meals, for a total daily dose of 6,000 mg. L-citrulline does not need to be taken with meals, however. To supplement for circulatory health with a citrulline malate supplement, take 1.76 g of citrulline malate for every 1 gram of citrulline you would normally take. To supplement L-citrulline to enhance sports performance, take 6,000 – 8,000 mg of citrulline malate about an hour before exercise. On days that you don't exercise, it can be broken up into smaller doses.

Dosage

Although the safety of long-term supplementation with high doses of citrulline warrants further investigation, research to date suggests that it is well tolerated in most individuals. Unlike arginine and ornithine, high doses of citrulline don't seem to result in gastrointestinal distress.

FAQs

What is citrulline?

What’s the difference between L-citrulline and citrulline malate?

L-citrulline is often combined with malate, an intermediary of the Krebs cycle. In theory, supplementing with malate could increase ATP production, potentiating L-citrulline's ergogenic effects. Although there has been some promising research showing that citrulline malate can improve exercise performance, it’s unclear whether citrulline malate is superior to citrulline, as there is currently no research directly comparing the two.

Which foods are rich in citrulline?

Citrulline is highest in watermelon, which contains an average of 2.1 milligrams of citrulline per gram of wet weight. Consuming watermelon has been noted to acutely increase both plasma arginine and citrulline.

Does citrulline improve exercise performance?

Citrulline has been touted as an ergogenic aid due to its promotion of vasodilation and blood flow by indirectly increasing nitric oxide synthesis. However, research on citrulline suggests that its effect on exercise performance is not as substantial as some claim.

Does citrulline reduce blood pressure?

Citrulline supplementation has been presented as a way of lowering blood pressure due to its capacity to boost nitric oxide production, a vasodilator. One meta-analysis does suggest that supplementation with citrulline can mildly decrease blood pressure, but more research is needed to see whether this decrease applies to people with high blood pressure.

Can citrulline help improve symptoms of erectile dysfunction?

Citrulline is thought to be a proerectile agent because it is a precursor for arginine, and arginine is the substrate from which nitric oxide is produced. In men with erectile dysfunction who were given 1,500 mg of citrulline daily, half of the participants reported a benefit.

Are there any side effects of taking high doses of citrulline?

In humans, a 15-gram dose of citrulline taken acutely does not appear to cause diarrhea or intestinal upset. In this respect, citrulline is notably different from both ornithine and arginine, which may cause diarrhea at 10-gram doses.

How is citrulline created in the body?

Citrulline is created in the body by one of two pathways, either recycled from arginine or produced from the nitrogen contained in L-glutamine.

Where is citrulline metabolized in the body after consumption?

The majority of citrulline either floats in the blood passively or is transported to the kidneys for conversion into arginine.

Does citrulline impact muscle protein synthesis?

Although citrulline does not appear to be an activator of mTOR, it does appear to restore muscle protein synthesis rates and muscular function after food restriction.

Does citrulline interact with other nutrients, supplements, or medications?

Branched-chain amino acids (BCAAs) are a group of three amino acids that are involved in skeletal muscle synthesis and degradation. Of these three, leucine is commonly said to be the most important.