Article edited for scientific accuracy by Illuminate Labs Blog Editor Taylor Graber MD
Citrulline is one of the most hyped supplements for performance improvement, and for good reason. There is a substantial amount of scientific evidence backing its effectiveness for athletes and regular people who perform either endurance or weightlifting exercise.
Citrulline (technically l-citrulline) is an amino acid. Malic acid is an organic compound found in fruits. Citrulline malate is an organic salt made from combining the two. There is more research on citrulline malate for workout improvements than citrulline alone, which is why most formulations use citrulline malate. In this review we will examine studies on both citrulline malate and l-citrulline, since the primary mechanism of action in both formulations is the nitric-oxide-boosting effects of citrulline.
Before taking any supplement, you should know about the science behind it, so we’re going to examine three benefits of citrulline malate supplementation based on a review of published medical research.
Exercise Benefit #1: Improved Endurance
Citrulline can help improve endurance during both aerobic (cardio) exercise and anaerobic (weightlighting) exercise. Citrulline is converted by the body to l-arginine, another amino acid. L-arginine is a nitric oxide (NO) precursor, so taking l-citrulline will increase NO levels. NO widens blood vessels and improves oxygen uptake in muscles during exercise.
A study from the Journal of Strength and Conditioning Research tested the effects of citrulline malate ingestion on weightlifters performing repetitions to failure. They found that the group taking citrulline malate performed significantly more reps in all three exercises than the control group taking placebo.
Japanese researchers tested the effect of citrulline in healthy, trained volunteers before and after cycling 4km. What they found was surprising. The group taking citrulline not only finished 1.5% faster (a significant difference for athletes), but had less fatigue after exercise. They were only taking 2.4g citrulline daily which is a relatively low amount. Since it’s already been established in previous research that citrulline has a dose-dependent response, the results probably would have been even more significant with a higher dose.
Exercise Benefit #2: Improved Strength
A meta-analysis of 12 different studies on citrulline’s effect on strength and power in an athletic context, published in Sports Medicine Journal, found that citrulline had a significant benefit relative to placebo. The effect size was relatively small, but still significant because objective strength gains from supplements are rarely seen.
Another study examined whether citrulline malate could improve the grip strength of female tennis players. The study found that maximal grip strength improved by about 3%, and average grip strength improved by about 4%. These numbers may seem small, but in the context of strength gains were quite surprising.
One great thing about citrulline malate is that it's very cheap and performs better than most expensive sports performance supplements like GF9, which we reviewed here.
Health Benefit #1: Reduced Blood Pressure
The same biological mechanism for improved aerobic capacity is what causes a blood-pressure-lowering effect of citrulline. When citrulline is converted into l-arginine, and then into NO, blood vessels widen and relax which drops blood pressure. Citrulline only lowers blood pressure in hypertensive (high blood pressure) patients, not in normotensive (health blood pressure) patients.
In 2018 a meta-study was conducted analyzing the effect of citrulline supplementation on various cardiometabolic factors. The researchers found several different anti-hypertensive effects of citrulline. They concluded that “supplementation with l-citrulline has shown promise as a blood pressure lowering intervention” after examining both animal and human studies.
The Journal of Cardiology in 2014 published a study on citrulline malate supplementation in patients with arterial hypertension. Arterial pressure dropped from 83.34mmHg to 79.1mmHg. The doses used in the study (1g taken three times daily) were low, so it’s impressive that a statistically significant result was achieved.
Health Benefit #2: Improved Blood Flow
A study in Experimental Physiology examined whether citrulline supplementation could improve blood flow during exercise in older adults. Blood flow increased by 11% in the study participants. Older adults have poorer blood flow generally so this is an important finding.
In 2017 there was a review published which sought to determine the influence of citrulline supplementation on vascular parameters. The scientists found that citrulline taken over the course of eight weeks improved brachial artery flow-mediated dilation (FMD)in patients with a heart condition. It achieved this result primarily by ameliorating endothelial dysfunction. In layman’s terms, this means that blood flow improved in patients with impaired blood flow.
Frequently Asked Questions About Citrulline
Should I Take Arginine and Citrulline Together?
One study in the Bioscience, Biotechnology and Biochemistry journal found that a combination l-arginine and l-citrulline supplement increased l-arginine levels more than l-citrulline supplementation alone. This suggests that arginine and citrulline taken in combination may increase nitric oxide levels more than citrulline alone. However this was one single study and we don’t recommend changing your supplement stack until more research confirms this.
Does Citrulline Help Bodybuilding?
Due to its positive effects on strength and exercised endurance, citrulline is likely to help bodybuilders improve their results. The supplement should be taken 30-60 minutes before exercise in a dose of 3g or greater.
Does Citrulline Work for Erectile Dysfunction (ED)?
There is preliminary research suggesting that citrulline supplementation may be beneficial for patients with ED. A study in the Urology journal found that citrulline improved erections in patients with mild ED. More robust research is needed for a conclusive answer.
One natural compound that's been studied more for ED benefit is Asian ginseng, though the dosages tend to be higher than when taken for nootropic effect (at least 1.5 g daily and usually higher based on medical research).
Should Citrulline be Taken With Pycnogenol?
There is no need for pycnogenol to be added for those taking citrulline for the exercise benefits. There is more research on pycnogenol than citrulline for ED benefit, but there also isn’t as much data on the safety of this compound, so we recommend sticking to citrulline supplementation alone.
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