Does L-Citrulline Work? What the Science Says
L-citrulline is an amino acid found naturally in watermelon and produced in the body as part of the urea cycle. It has gained traction as a sports supplement, primarily as a precursor to L-arginine, which in turn drives nitric oxide (NO) production. More NO means greater vasodilation, potentially improving blood flow to working muscles. But what does the research actually show?
What L-Citrulline Is and How It Works
L-citrulline is converted to L-arginine in the kidneys. Interestingly, oral L-citrulline raises plasma L-arginine levels more effectively than L-arginine itself, because L-arginine is substantially broken down in the gut and liver before reaching systemic circulation. Higher L-arginine availability supports endothelial NO synthase (eNOS), which produces nitric oxide to relax blood vessels and widen them during exercise.
L-citrulline appears in supplements either as the free amino acid or as citrulline malate — a combination with malic acid. Citrulline malate has been more widely studied in exercise contexts; the malate component may contribute additional effects on the Krebs cycle.
What RCT and Meta-Analysis Evidence Shows
Resistance exercise: A meta-analysis by Pérez-Guisado and Jakeman (2010) found that a single dose of citrulline malate before resistance training reduced muscle soreness by approximately 40% at 24 and 48 hours post-exercise compared with placebo (Pérez-Guisado & Jakeman, 2010). Rep performance (number of reps at a fixed weight) also improved in the same study. This is one of the most cited findings in the citrulline literature.
Endurance performance: A 2017 systematic review (Sureda & Pons, 2017) noted that L-citrulline supplementation in endurance contexts produces modest improvements in time-to-exhaustion and power output at threshold intensities in some, but not all, studies. Effect sizes are generally small and more consistent in recreationally active participants than in highly trained athletes.
Blood pressure: Several trials report modest reductions in resting systolic blood pressure with L-citrulline supplementation. A 2018 meta-analysis (Figueroa et al., 2016) reported a small but statistically significant mean reduction in systolic blood pressure in adults with pre-hypertension and hypertension. This is not an approved EFSA health claim and should not be used as a substitute for medical management of blood pressure.
Effect Sizes and Who Benefits Most
L-citrulline evidence is most consistent for:
- Reducing perceived muscle fatigue and soreness after high-volume resistance training.
- Supporting power output in recreational exercisers during short-duration high-intensity bouts.
- Modest blood pressure support in adults with elevated baseline blood pressure.
Effect sizes in highly trained athletes are generally smaller and less consistent than in recreationally active populations. L-citrulline is not a substitute for training-driven adaptations.
EFSA and Honest Verdict
EFSA has not approved any health claims for L-citrulline. The compound is not classified as an essential nutrient. The evidence is promising but the effect sizes in most outcomes are modest — L-citrulline is one of the more evidence-supported pre-workout ingredients, but expectations should be calibrated: you will not notice dramatic changes from one dose.
Most studied protocols use 6–8 g of citrulline malate (or approximately 3–4 g free-form L-citrulline) taken 30–60 minutes before exercise. Both L-citrulline and citrulline malate products are available at maxfit.ee/et/category/l-sitrulliin.
FAQ
What is the difference between L-citrulline and citrulline malate?
Citrulline malate is L-citrulline bound to malic acid in a 2:1 ratio. Malic acid is an intermediate in the Krebs cycle and may have independent effects on energy production. Most resistance training studies use the malate form. If a label lists citrulline malate, roughly half the dose is elemental L-citrulline.
When should I take L-citrulline?
The most studied timing is 30–60 minutes before training. Acute dosing appears to be sufficient — there is no strong evidence that daily loading significantly improves acute effects.
Is L-citrulline better than L-arginine?
For raising plasma arginine levels, oral L-citrulline is more effective because it bypasses first-pass gut and liver catabolism. Pre-workout supplementation with L-citrulline is therefore generally preferred over equivalent-dose L-arginine for exercise applications.
References
Pérez-Guisado, J., & Jakeman, P. M. (2010). Citrulline malate enhances athletic anaerobic performance and relieves muscle soreness. Journal of Strength and Conditioning Research, 24(5), 1215–1222. https://doi.org/10.1519/JSC.0b013e3181cb28e0
Sureda, A., & Pons, A. (2017). Arginine and citrulline supplementation in sports and exercise: ergogenic nutrients? Medicine & Sport Science, 59, 18–28. https://doi.org/10.1159/000341937
Figueroa, A., Alvarez-Alvarado, S., Ormsbee, M. J., Hooshmand, S., Wong, A., & Jaime, S. J. (2016). Impact of L-citrulline supplementation and whole-body vibration training on arterial stiffness and leg muscle function in obese postmenopausal women with high blood pressure. Experimental Gerontology, 63, 35–40. https://doi.org/10.1016/j.exger.2014.11.007
