The Potential Benefits of Citrulline
Citrulline is a non-essential amino acid that’s found mainly in watermelon. In the body, citrulline acts as a precursor to another amino acid, arginine. Arginine is used in the production of nitric oxide. Nitric oxide is a signaling molecule with numerous functions. In the bloodstream, nitric oxide acts to dilate the blood vessels, decreasing blood pressure and increasing blood flow to organs and tissues. As such, citrulline is a way to increase nitric oxide production and improve blood flow.
Due to its potential benefits, citrulline has been investigated for its athletic performance enhancing abilities and its effects on blood pressure, although results are very modest at best. In reality, citrulline looks to have more promise in the treatment of sexual dysfunction, blood sugar problems and inflammation, although studies are still limited.
Citrulline for Athletic Performance Enhancement
While the research isn’t completely clear cut, the majority of the research shows minimal benefits for athletic performance with citrulline supplementation. For muscle strength during resistance training, the most recent meta-analysis found no benefits with citrulline (Aguiar 2022). However, a separate analysis did find a small benefit for increased repetitions, but only for the lower body (Vårvik 2021).
For aerobic exercise, citrulline did not show any significant benefits, although there was a trend towards improvements with long-term exercise protocols (Viribay 2022). A separate meta-analysis on endurance in young athletes with citrulline supplementation also failed to find any significant effects (Harnden 2023).
While most of the studies suggest minimal benefits, a meta-analysis on overweight older adults who combined citrulline with exercise found significant benefits over exercise alone for improving strength (Xie 2023). Still, the benefits from citrulline were modest, consisting of only small improvements over placebo.
While there is a fair amount of hype about using citrulline as an aid for athletic performance enhancement, the research doesn’t suggest much in the way of real-world benefits. It’s probably worth considering citrulline supplementation for uses other than athletic performance.
Blood Pressure Effects of Citrulline
Similar to athletic performance enhancing effects, the benefits of citrulline on blood pressure are quite modest. A recent meta-analysis found that citrulline only lowered the bottom (diastolic) blood pressure number significantly by just 2.75 points (Barkhidarian 2019). Dosing had to be six grams or more per day to achieve the effects. While any reduction in blood pressure is helpful, there are other natural alternatives for high blood pressure that appear more effective than citrulline.
Citrulline and Erectile Dysfunction
Arguably, citrulline may hold promise for treating erectile dysfunction. In the research, it is often combined with arginine for treatment. A study out of Japan found improved sexual function in healthy males over twelve weeks with a combination supplement (Najima 2016). Blood flow velocity along with sexual function were improved, although testosterone levels were unchanged.
A study on fairly low doses of citrulline at just 1.5 grams per day found improvements in mild erectile dysfunction (Cormio 2011). When taking citrulline, 50% of the men were able to engage in normal sexual intercourse. While it was less effective than prescription Viagra, citrulline still provided significant improvements.
Arginine supplementation alone has been found to be effective for mild to moderate erectile dysfunction (Rhim 2019). Due to its rapid breakdown when taken orally however, arginine supplementation is not necessarily the best choice. Research actually suggests citrulline is more effective for raising arginine levels in the blood by acting as a precursor (Schwedhelm 2008). While we need more research for confirmation, due to its effects on blood levels, citrulline may be the better choice for erectile dysfunction treatment overall.
Other Benefits of Citrulline
Insulin resistance is the core problem in type 2 diabetes. As a hormone, insulin acts to shunt blood sugar into the cells for use in energy production. When insulin resistance is present, insulin is less effective. In overweight patients with diabetes, citrulline supplementation had a fairly large effect on reducing insulin resistance and levels of inflammation (Azizi 2021). In the study, Insulin resistance was reduced 38%, while levels of the inflammatory marker, C-reactive protein, were reduced 65% with three grams of citrulline per day.
In patients with non-alcoholic fatty liver disease, citrulline was also effective at dropping levels of chronic inflammation (Darabi 2019). With dosing of just two grams total per day, levels of inflammation measured by C-reactive protein decreased by 32%.
Conclusion
While studies on improving exercise performance and blood pressure are quite modest, citrulline may still be helpful for other conditions. Data suggests some promise for treating erectile dysfunction, reducing insulin resistance and decreasing chronic inflammation. Hopefully, research can start to focus more on the areas where citrulline appears effective to help confirm the findings.
