L-citrulline is a nutrient and dietary supplement that has fast grown in popularity over the last decade. Produced naturally in the body, L-citrulline is a non-essential amino acid that helps the body improve blood flow. The body converts L-citrulline into L-arginine, which creates nitric oxide, a gas that helps dilate blood vessels. This dilation can result in numerous health benefits.
The body produces sufficient levels of L-citrulline to meet the needs of most individuals. Its vessel widening abilities have seen claims of enhanced athletic performance, improved symptoms of erectile dysfunction and cardiovascular health properties. But is there evidence to support the claims?
Reported Effects of L-Citrulline
1. Athletic Performance
Due to its blood flow increasing abilities, research suggests that L-citrulline results in reduced fatigue and improved endurance for both aerobic and anaerobic exercise.
Endurance: A single dose does not seem to have any effect on exercise performance, however two weeks of supplementation can significantly increase the oxygen content in muscle [1][2]. In layman’s terms, more oxygen in the muscle = more energy production, which offers better exercise performance.
This has been shown in cycling studies, where cyclists supplementing with L-citrulline were able to cycle 12% longer before exhaustion than their counterparts taking a placebo [3].
Weight Training: Although L-citrulline isn’t an amino acid used directly to build proteins, it has been shown to increase protein synthesis by stimulating an important signalling pathway involved in muscle building [4] This suggests a potential benefit for weight training performance.
One study found that after ingesting citrulline malate participants were able to perform 53% more repetitions versus a placebo. What’s more, they reported that muscle soreness in the two days after exercise was 40% lower than those without having ingested citrulline malate. [5].
It is worth considering that much of the evidence for the beneficial effects of L-citrulline on strength training comes from studies using citrulline malate. This is the combination of citrulline and malate, an important compound for energy production.
This does mean that it is difficult to attribute which benefits are due to citrulline, and which are due to malate.
2. Cardiovascular Health
Similar to findings in athletic performance, a single dose of L-citrulline has very little effect on cardiovascular health. A single dose does not improve the ability of the of arteries to widen. Supplementing over time however, has shown drastic improvements in the widening ability of arteries [6]. This widening can potentially improve blood pressure and flow, allowing for a happier, healthier heart.
L-citrulline can also decrease blood pressure, particularly for individuals with high blood pressure – anywhere from 4-15% after just eight weeks [7]. For healthy individuals, the evidence is less clear-cut, with the results varied.
3. Erectile Dysfunction
L-citrulline also has pro-erectile properties, due to its beneficial effect on blood vessels.
In men with erectile dysfunction, over 50% were very satisfied with the treatment when given L-citrulline daily, versus a mere 8% who were given a placebo [8].
Common Supplements that Contain L-citrulline
L-Citrulline can be found in various supplements. Most notably, it can be found as a stand-alone supplement in tablet form, often marketed as a ‘pump enhancer’.
Due to the increased blood flow, it is widely recognised in the fitness community as a ‘pump’ ingredient. Because of this, it’s also highly prevalent in pre-workout supplements.
You’ll also find it in Citrulline Malate, a cheaper alternative, also often marketed as a pre or intra-workout powder.
Side Effects of L-Citrulline Supplementation
As L-citrulline occurs naturally in the body, it is widely considered a safe supplement. It appears to be well tolerated; no toxic effects have been reported when taking the recommended dosage. Supplementation may cause mild symptoms such as:
- stomach upset
- heartburn
- cough
- changes in urination
There isn’t enough evidence to determine whether or not L-citrulline is safe to use when pregnant, until more is known, avoid while pregnant or breast feeding.
It’s also worth considering that L-citrulline will have an effect on the same bodily functions as some drugs used to treat high blood pressure, cardiovascular disease and erectile dysfunction.
L-Citrulline Dosage
The current recommended dose is 3–6 grams per day of L-citrulline or approximately 8 grams per day of citrulline malate, but this will vary dependent on usage:
- Weight training: 8 grams of citrulline malate provides ~4.5 grams of L-citrulline, which is an effective dose for improving weight training performance [9].
- Oxygen in muscle: To improve the oxygen content in muscle, 6 grams of L-citrulline per day appears to be effective [3].
- Blood pressure: For improving blood pressure, the daily dose of L-citrulline used in research is typically 3–6 grams.
Up to 15 grams per day has shown no side effects, but evidence has shown there is no additional benefits consuming 10g or more per day, as there is a limit to how much the body can use [10].
References
- Figueroa A, Wong A, Jaime SJ, Gonzales JU. Influence of L-citrulline and watermelon supplementation on vascular function and exercise performance. Curr Opin Clin Nutr Metab Care. 2017;20(1):92‐98.
- Bailey SJ, Blackwell JR, Lord T, Vanhatalo A, Winyard PG, Jones AM. l-Citrulline supplementation improves O2 uptake kinetics and high-intensity exercise performance in humans. J Appl Physiol (1985). 2015;119(4):385‐395.
- Bailey SJ, Blackwell JR, Lord T, Vanhatalo A, Winyard PG, Jones AM. l-Citrulline supplementation improves O2 uptake kinetics and high-intensity exercise performance in humans. J Appl Physiol (1985). 2015;119(4):385‐395.
- Bahri S, Zerrouk N, Aussel C, et al. Citrulline: from metabolism to therapeutic use. Nutrition. 2013;29(3):479‐484.
- Pérez-Guisado J, Jakeman PM. Citrulline malate enhances athletic anaerobic performance and relieves muscle soreness. J Strength Cond Res. 2010;24(5):1215‐1222.
- Kim IY, Schutzler SE, Schrader A, et al. Acute ingestion of citrulline stimulates nitric oxide synthesis but does not increase blood flow in healthy young and older adults with heart failure. Am J Physiol Endocrinol Metab. 2015;309(11):E915‐E924.
- Orozco-Gutiérrez JJ, Castillo-Martínez L, Orea-Tejeda A, et al. Effect of L-arginine or L-citrulline oral supplementation on blood pressure and right ventricular function in heart failure patients with preserved ejection fraction. Cardiol J. 2010;17(6):612‐618.
- Cormio L, De Siati M, Lorusso F, et al. Oral L-citrulline supplementation improves erection hardness in men with mild erectile dysfunction. Urology. 2011;77(1):119‐122.
- Pérez-Guisado J, Jakeman PM. Citrulline malate enhances athletic anaerobic performance and relieves muscle soreness. J Strength Cond Res. 2010;24(5):1215‐1222.
- Moinard C, Nicolis I, Neveux N, Darquy S, Bénazeth S, Cynober L. Dose-ranging effects of citrulline administration on plasma amino acids and hormonal patterns in healthy subjects: the Citrudose pharmacokinetic study. Br J Nutr. 2008;99(4):855‐862.