Citrulline is a non-essential amino acid, meaning that the body can manufacture it from other nutrients. Within the body, citrulline is converted to the amino acid L-arginine. Arginine creates nitric oxide (NO), a chemical that dilates blood vessels. Some of the proposed uses of citrulline supplements are based on raising levels of arginine. Citrulline also plays a role in a physiological process called “the urea cycle,” in which toxic ammonia is converted to urea.

Requirements/Sources

The body manufactures citrulline from the essential amino acid glutamine. Deficiency of citrulline is unlikely to occur.

Therapeutic Dosages

A typical dose of citrulline is 6–18 grams daily. It is commonly sold in the form of citrulline malate.

Therapeutic Uses

Dilated blood vessels improve blood flow, blood pressure, and oxygen delivery to muscles. This is the basis of using it to enhance sports performance. Much of the science to support citrulline supplements for this purpose is promising, but the trials were small (less than 25 people), which makes it harder to determine if the results are conclusive or just random chance. In addition, the participants were active on a regular basis or trained athletes so it is not clear if these benefits would extend to people with all levels of fitness.

A handful of randomized trials found that citrulline supplements did reduce muscle fatigue while improving endurance, overall performance, and time to recovery when compared to placebo1-5,7,9. One randomized trial found similar results using watermelon juice enriched with citrulline.8 However, one trial found no benefit with consuming watermelon juice concentrate alone.6

Nitric oxide (NO) sensitivity plays a part in the ability to achieve and maintain an erection. This could lead one to believe that citrulline supplements may be helpful for men with impotence. One randomized trial found this to be the case when compared to placebo. Again, the trial had less than 25 participants with mild impotence, which makes it less reliable. In addition, placebos alone can be effective for some men. It was not indicated if impotence related to physical or psychological factors.10

Safety Issues

As a naturally occurring amino acid, citrulline is believed to be safe. However, maximum safe doses in young children, pregnant or nursing women, or people with severe liver or kidney disease have not been established.