Written By: Ashley Gunderson – Dietetic Intern University of Houston
Edited By: Brett Singer MS, RD, CSSD, LD - Memorial Hermann IRONMAN Sports Medicine Institute.
What this article will discuss:
- Citrulline is an ingredient often found in various multi-ingredient supplements
- The article will highlight potential uses of citrulline, and where evidence currently stands regarding dosage and potential benefit
In some capacity, most people have heard of dietary supplements. You may take them for some sort of nutrient deficiency, or perhaps as an ergogenic aid to enhance athletic performance. Dietary supplements can be beneficial in a variety of ways IF used correctly. Popular supplements with strong evidence for performance benefits include creatine, caffeine, and protein, to name a few. One supplement that has sparked recent interest among athletes and researchers is an amino acid known as citrulline. Citrulline can often be found in pre-workout supplements or as an addition to other supplement ingredients. Given that the hype about citrulline is still growing, limited research has been done, and potential benefits are still unclear. So, let's take some time to review the research on citrulline and if it may be beneficial for you.
So what is citrulline, exactly?
Citrulline is a non-essential amino acid that can be changed in the body into another more commonly known amino acid known as arginine. Amino acids are classified as one of two things: essential or non-essential, where essential amino acids are ones that your body cannot produce itself and therefore must be obtained in the diet. Citrulline, however, is considered a ‘non-essential’ amino acid meaning it is naturally produced in the body and therefore you do not need to obtain it in the diet. While your body naturally produces citrulline, it can still be found in select food sources such as watermelon and is often added in other items such as pre-workout or protein bars.
Why take it?
Citrulline is thought to have benefits because of its upregulation of nitric oxide synthesis. Nitric oxide assists in improving blood flow in the body, which aids in the delivery of oxygen and energy, therefore possibly improving athletic performance by decreased feelings of fatigue. While your body already produces citrulline on its own, some studies have investigated the potential benefits of taking citrulline supplementation for select athletes.
The studies show…
The rising interest in citrulline has prompted more research to determine the potential benefits of citrulline supplementation and its effect on athletic performance. Does citrulline benefit all types of athletic performance? Or does it provide benefits that are applicable only to certain types of exercise?
One study done on trained male cyclists showed that participants taking a citrulline supplement one hour before exercise improved 4-km cycling time trial performance when compared to when they took a placebo. Additionally, perceived muscle soreness was lessened in the citrulline supplementation group compared to the placebo group (Suzuki et. al., 2016). A different study by Chen et. al., measured the effects of anaerobic performance and recovery on tae kwon do athletes and found that a citrulline supplement combined with arginine and the branched chain amino acids (BCAA) leucine, isoleucine and valine reduced the exercise-induced central fatigue in certain elite athletes. This study also tested reaction time and speed to complete a set of tae kwon do moves, and found improved reaction time and decreased time to completion of the movements (2016). While this study showed promising results, it only tested a specific sport population and also incorporated BCAA supplementation in addition to the citrulline, which makes it difficult to draw strong conclusions on whether citrulline was the primary factor in performance improvement.
A different study was conducted on master female tennis athletes testing impacts of an 8g citrulline supplementation on grip strength, power, and anaerobic cycling performance.
The anaerobic cycling test found significant increases in explosive and relative peak power, however, no significant differences were found when testing for sustained anaerobic power when comparing the citrulline group to the placebo group. Additionally, grip strength was also improved among those tennis players consuming the citrulline supplement (Glenn et. al., 2016).
Studies testing various potential benefits of citrulline supplementation as an ergogenic aid have shown potential performance benefits in regards to explosive power, grip strength, and decreased muscle soreness. While some research shows that citrulline may aid in athletic performance, the research on citrulline has primarily only been done on a few specific sports, most of which are anaerobic. This makes it difficult to draw any conclusions on if citrulline is beneficial for any athlete, as they have not tested every sport and those sports that have been studied have not been studied enough.
Studies on citrulline supplementation have shown positive effects in doses as small as 2.4g before a performance (Suzuki et. al., 2016). On the other hand, a majority of other studies have tested higher doses, varying from 8g to upwards of 12g, while still finding benefits (Rhim et. al., 2020). While many studies have taken the approach with a set dosage, the study by Chen et. al. gave doses of citrulline supplementation based on grams per kilogram of the subject, making each subject have varying intakes of citrulline (2016). This approach makes it difficult to determine if there is a generalized ideal dose, however, it does factor in each athlete’s unique needs and therefore may provide better benefits. Due to this wide range in doses, with no clear consensus, it is clear that more evidence is needed in regards to what is an acceptable dose of a citrulline supplement to see any type of athletic improvements.
If you are an athlete or active individual, a citrulline supplement may be beneficial for you depending on the type of exercise you are doing. Of these few studies done on citrulline supplementation, there have been promising results in regards to acute citrulline supplementation on both male and female athletes performing an anaerobic exercise. Whether these results transfer to all levels of athletes or longer duration sports remains in question at this time. Despite promising results, it appears further research is warranted to provide more specific recommendations for dosing, frequency, timing, and type of athletes who may benefit most from citrulline. Whether or not citrulline proves to be an effective ergogenic aid for you, remember that supplements are not to be used in place of a healthy diet, and it is crucial to focus on obtaining nutrients from food first.
Chen, I., Wu, H., Chen, C., Chou, K., & Chang, C. (2016). Branched-chain amino acids, ARGININE, Citrulline alleviate central fatigue after 3 Simulated matches in TAEKWONDO athletes: A randomized controlled trial. Journal of the International Society of Sports Nutrition, 13(1). doi:10.1186/s12970-016-0140-0
Glenn, J. M., Gray, M., Jensen, A., Stone, M. S., & Vincenzo, J. L. (2016). Acute citrulline-malate supplementation improves maximal strength and anaerobic power in female, masters athletes tennis players. European Journal of Sport Science, 16(8), 1095-1103. doi:10.1080/17461391.2016.1158321
Rhim, H. C., Kim, S. J., Park, J., & Jang, K. (2020). Effect of citrulline on post-exercise rating of perceived exertion, muscle soreness, and blood lactate levels: A systematic review and meta-analysis. Journal of Sport and Health Science, 9(6), 553-561. doi:10.1016/j.jshs.2020.02.003
Suzuki, T., Morita, M., Kobayashi, Y., & Kamimura, A. (2016). Oral l-citrulline supplementation enhances cycling time trial performance in healthy trained men: Double- blind randomized placebo-controlled 2-way crossover study. Journal of the International Society of Sports Nutrition, 13(1). doi:10.1186/s12970-016-0117-z