Citrulline supplements are most often marketed to people who are trying to enhance athletic performance. You’ll also see citrulline sold as a sexual performance enhancer and as a supplement that’s useful for its ability to combat issues related to heart disease, such as high blood pressure. Science backing any of these uses is scanty, however, so check with your doctor before trying this supplement for any purpose.
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Citrulline is an amino acid, but it is not an essential one. That means your body can manufacture it on its own from glutamine, which is an essential amino acid. Citrulline is converted within your body to L-arginine. Some uses for citrulline are based on its ability to boost arginine levels in your body, says Steven Bratman, author of the “Collins Alternative Health Guide.”
When citrulline is sold as an athletic performance booster, it is billed as the aerobic compliment to the supplement creatine, which enhances high-intensity, or anaerobic, performance. The theory behind the heart-health is based on its ability to raise arginine levels, which in turn boosts your body’s production of nitric oxide, according to the book, “NO More Heart Disease,” by Louis J. Ignarro and Louis Ignarro.
The authors say nitric oxide is a vasodilator that can help control blood flow to all parts of your body. According to Ray Sahelian, M.D., of Los Angeles, California, the hype over citrulline as a sex enhancer originated in July 2008.That’s when a Texas A&M researcher was quoted in the media comparing watermelon to the erectile dysfunction medicine Viagra, saying that the citrulline in watermelon, once converted to arginine, boosts nitric oxide levels and relaxes blood vessels, which is comparable to Viagra's effect.
The common dosage for therapeutic use is typically 6 to 18 g daily. However, recommendations vary. For example, according to the Ignarros, you should take 200 to 1,000 mg daily before bed. Citrulline malate is the most common form on the market. Maximum doses for cirtulline have not been established, Bratman notes.
Supplementing with citrulline may be safer than supplementing with arginine when you need to raise levels of the latter in the body, notes S. Osowska, lead author for a study published in the gastroenterology journal, “Gut.” That’s because arginine is captured and metabolized by your liver whereas citrulline passes freely to your kidneys where it gets converted to arginine, Osowska says. Your gut and your liver are the two main organs that metabolize arginine.
The evidence for this supplement’s benefits is mostly anecdotal. Scientific support for using citrulline supplements to improve sports performance is lacking because few studies exist, Bratman says. Also, among studies that do exist, some evidence points to this supplement reducing instead of enhancing performance, Bratman says. It’s effectiveness as an impotence treatment is questionable as well because evidence supporting arginine for this condition, which citrulline is supposed to boost, is weak.