Citrulline benefits: From gym pumps to erectile function, what the evidence shows

Are you a gym junkie looking to accelerate your progress?

It’s easy to get lost in all the supplement hype, especially if you take a glance at social media. Today, one in three Aussies takes at least one supplement a year, and L-citrulline is just one popular supplement [1].

But what does it do, what are the health benefits of citrulline, and what’s the evidence to back up the claims?

What is L-citrulline?

L-citrulline is a non-essential amino acid your body makes naturally. Unlike other plasma amino acids, though, it isn't involved in protein synthesis. Interestingly, it comes from the Latin name “citrullus”, which is translated as “watermelon”.

It’s also the precursor of arginine, which is why when you opt for oral L-citrulline supplementation, your arginine levels increase [2]. It’s chiefly known for enhancing nitric oxide synthesis, which may improve oxygen and nutrient delivery to muscle tissue, hence its promotion as an exercise enhancer [3].

Beyond that, it’s also promoted as something that can delay fatigue by increasing the rate at which your body clears out lactate and ammonia [4]. Some studies have even gone as far as to investigate the link to how it might interact with aspects like heart health and erectile dysfunction (ED) [5].

Benefits of citrulline: L-citrulline vs. citrulline vs. citrulline malate

All three of these terms are talking about the same amino acid. When you see these terms in the supplements aisle and end up scratching your head, don’t worry, because they’re largely the same thing.

L-citrulline, or left-handed citrulline, is just the pure molecular form that your body uses. Citrulline malate, on the other hand, is just citrulline bound with another supplement called malic acid.

Adding malic acid is done to add energy-boosting benefits. Since malic acid plays a role in the process of making energy for your cells, you might see reduced fatigue and more physical stamina [6].

How does L-citrulline work in the body?

Chug some L-citrulline, and the supplement goes directly into your small intestine. You might be wondering, since it’s the precursor to arginine, why not just take an arginine supplement instead?

It’s actually better to take L-citrulline because it bypasses being broken down by the liver and goes straight into your small intestine. Once it’s in your bloodstream via your kidneys, it gets converted into L-arginine anyway [7].

So, what happens next? Here’s a rundown of what your body does [8]:

1. Your kidneys synthesise L-arginine
2. L-arginine enters your circulatory system
3. Cells in the inner lining of your blood vessels start producing nitric oxide
4. Nitric oxide is a signalling molecule that causes vasodilation

Vasodilation matters because it essentially means widening your blood vessels. And that’s where citrulline benefits come from because it lets the blood flow more freely.

L-citrulline supplements vs. L-arginine supplements: What’s the difference?

L-citrulline and L-arginine are both amino acids. They share the function of increasing nitric oxide levels to improve blood flow. In fact, citrulline is actually the precursor to arginine. The difference is that citrulline doesn’t get stuck trying to make its way through the liver and the gut, where it becomes degraded [9].

That’s why modern supplementation doesn’t involve just taking L-arginine and calling it a day. The bioavailability of L-citrulline as a nonessential amino acid is much higher because it’s not going through the liver but through the kidneys.

What are the health benefits of L-citrulline?

Boosting nitric oxide production is the primary reason L-citrulline may have genuine health benefits, as supported by a variety of studies. But it’s always vital to get into the science itself because social media will issue plenty of claims, and the last thing you want is to be relying on that old chestnut of “trust me, bro” all over again.

So, here are the potential benefits of adding a few grams of L-citrulline to your diet.

Blood pressure, flow, and circulation

Firstly, L-citrulline plays a pivotal role in producing nitric oxide. It’s well-established that this compound causes the blood vessels to expand, which is why blood flow and circulation are enhanced when your body has sufficient levels of nitric oxide in the blood.

But where do we stand on lowering blood pressure?

In short, there’s a tentative link between lower blood pressure and L-citrulline intake. In one review of eight studies, taking citrulline supplements at lower doses did reduce systolic blood pressure [10].

That doesn’t mean if you’ve got high blood pressure, you can take a few pills and call it a day. See blood pressure control as a potential bonus rather than a miracle alternative.

Boost exercise performance and recovery

Exercise performance and accelerated recovery are the two primary reasons L-citrulline is such a popular supplement in gyms across Oz. The body is incredibly efficient at converting citrulline into arginine, failing to convert only about 20% of citrulline [11].

The theory behind this benefit is that higher nitric oxide levels may increase blood flow. More blood flow means your muscles receive more oxygen and nutrients [12]. But that only matters if it leads to more muscle oxygenation and overall oxygen uptake.

Smaller studies have found that L-citrulline supplementation improves athletic performance in a variety of aerobic exercise disciplines, including weightlifting and cycling. Likewise, the same study found that people taking this supplement reported that it relieves muscle soreness [13].

Erectile function 

Maintaining an erection in the bedroom can be a challenge for a lot of blokes. In theory, increased blood flow could enhance erectile function, too. In this area, the results are relatively mixed.

There’s one small study that found men with mild erectile dysfunction saw improved erection hardness [14]. However, the results have been mixed, and there haven’t been huge numbers of large-scale studies into it.

Instead, you might want to consider other options by speaking to your GP. Talking to your doctor can unlock other options, including prescription medications, therapy, and access to clinician-led solutions like Pilot’s ED treatment. 

Food sources of L-citrulline

It shouldn’t surprise you that the undisputed champion of citrulline comes from its namesake, watermelon. By far, it’s the primary natural food source for it, so if you’re not looking to add more supplements to your diet, eating watermelon daily, or even watermelon juice supplementation, can get your body its fix of L-citrulline.

Note that the amount you get depends on the type of watermelon, with one study finding that Dixielee and Crimson Sweet are varieties particularly high in citrulline [15]. Some other foods that also contain this amino acid include:

• Cucumber
• Pumpkin
• Squash

Additionally, all other types of melons contain varying degrees of L-citrulline, but none are on the level of watermelon in terms of overall dietary intake.

Is L-citrulline safe? Side effects and who should avoid it

L-citrulline naturally occurs in your body already. The left-handed form of citrulline is the free form of the amino acid that the human body actually uses as part of producing nitric oxide to keep the machine pumping.

So, if you’re worried about adding some artificial compound to your diet, L-citrulline administration shouldn’t give you any cause for concern. It’s also why there are no documented side effects for most people. However, because of its effect on blood pressure, certain groups should consult their doctors first.

Talk to your doctor before adding L-citrulline dietary supplements if you:

• Are already taking blood pressure or heart medications for some other condition
• Take prescription ED drugs, as L-citrulline might interfere with their mechanisms
• Have any form of severe organ disease, particularly involving the kidney or liver
• Already have potentially low baseline blood pressure

Since L-citrulline is already naturally present in the body, you’re not consuming something that isn’t already there. The only real cause for concern is if you already have an underlying medical condition, meaning that you should speak to your doctor, as supplementation will result in higher L-citrulline and nitric oxide levels.

When to speak to a doctor about erectile dysfunction

Are you worried about how erectile function is impacting your experience in the bedroom?

ED is more common than you might think, with an estimated 25% of all blokes having some form of ED [16]. It’s also more common as you get older, with roughly a third of men over the age of 40 and over six in ten men aged 45 and older having some form of ED [17].

With that in mind, you might be looking to supplements as a solution. Although supplementation might relieve symptoms of mild ED, it’s important to get the support that suits your situation. That’s why if you’ve got persistent problems or it’s causing distress, it’s time to take action.

Get in touch with your GP to talk about erectile dysfunction and get a consultation that will unearth the source of the problem and provide a potential way forward.

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