L-Arginine vs L-Citrulline: Which Is Better?

L-arginine and L-citrulline are amino acids that play essential roles in your body’s nitric oxide production. 

Nitric oxide is a gas molecule that helps blood vessels relax and dilate their vascular smooth muscle cells, which improves blood flow. 

By improving blood circulation, L-arginine and L-citrulline can help alleviate symptoms of high blood pressure, enhance sexual health, and ease symptoms of diabetes.

But which one is better? Should you take both to see the effects on your body? 

In this article, we will explore the arginine and citrulline basics and the differences between L-arginine vs L-citrulline so you can choose which supplement is right for you.

What is L-arginine?

L-arginine is an essential amino acid required for many bodily functions. 

It is found in various food sources, including meats, fish, dairy, eggs, and certain vegetables. It’s also available in supplement form. 

It is a precursor of nitric oxide, a potent vasodilator, which is responsible for the regulation of blood flow. 

L-arginine is produced in the body from the amino acid L-citrulline through the action of various enzymes.

Then, nitric oxide synthesis uses L-arginine through the enzyme nitric oxide synthase. 

Once synthesized and released, nitric oxide has many important functions in the body, including regulating blood pressure, immune system function, and cell signaling.

Thus, it is no surprise that L-arginine has been linked to improved cardiovascular health, muscle performance, and sexual function. It has also been used to treat kidney and liver disorders.

RELATED: Does L-Arginine Help With Erectile Dysfunction?

What is L-citrulline?

L-citrulline is an amino acid closely related to L-arginine. It is found naturally in foods like watermelon, pumpkin seeds, and nuts and can also be taken as a dietary supplement. 

The body uses L-citrulline to produce L-arginine, which is then converted into nitric oxide, a substance with the above functions.

Athletes and bodybuilders mainly use this supplement because it may improve muscle performance and endurance. 

Additionally, L-citrulline may benefit people with cardiovascular disease, as it may help improve blood flow and reduce inflammation.

And even if you’re not an athlete, the benefits of L-citrulline can help. One study looked at L-citrulline in older adults with blood circulation problems in their legs. 

The researchers reported that 14 days of L-citrulline were enough to increase femoral blood flow by 11%. 

Moreover, the muscles and blood vessels became 14% more responsive to lower limb exercise in these patients.

RELATED: Erectile Dysfunction and L-Citrulline: What You Should Know.

L-arginine vs L-citrulline Comparison

In this section, we compare L-arginine vs L-citrulline and their uses, differences, similarities, and effectiveness.

Uses

As mentioned above, both amino acids have a role in the synthesis of nitric oxide (NO) in the body, which is essential for blood flow regulation, immune system functioning, and the regulation of the nervous system.

Nitric oxide is produced by the enzyme nitric oxide synthase (NOS) from L-arginine. Still, since L-citrulline can produce L-arginine, both increase plasma nitric oxide levels and have similar uses. You can say they go through the same pathway but from different standpoints.

L-arginine as a supplement or nutrient is used to improve sexual health, increase blood circulation, achieve better control of blood pressure levels, boost the immune system, and protect the organism against cardiovascular diseases.

Citrulline malate has the same applications vs L-arginine, but athletes also use it to improve their stamina and physical performance. 

And, as mentioned above, even if you’re not an athlete, your muscles can become more responsive to exercise by increasing their blood flow.

Compared to L-arginine, L-citrulline has better evidence in strength and conditioning research. 

Despite being one step away from nitric oxide compared to L-arginine, L-citrulline is thought to remain untouched for longer, which extends the range of uses we can give this supplement.

Differences

L-arginine is a semi-essential amino acid, meaning it can be made in the body, but it should also be acquired from food sources. 

It is the direct precursor for nitric oxide production, meaning it is the molecule that is first used in synthesizing nitric oxide.

On the other hand, L-citrulline is an essential amino acid, meaning it has to be obtained through food or dietary supplementation. It is not synthesized in any way by the organism. 

Instead of directly producing nitric oxide, L-citrulline is the primary molecule used to synthesize L-arginine, which then maintains your nitric oxide levels.

Studies have found that L-citrulline is more effective at increasing nitric oxide levels in the body than L-arginine, making it a more desirable option for those looking to improve blood flow and heart health. 

Additionally, because of its unique metabolic pathway, L-citrulline has been shown to be more effective than L-arginine in reducing fatigue, muscle soreness, and post-exercise recovery time.

Similarities

As noted above, both of these amino acids are important for the production of nitric oxide. 

However, they approach this in different ways. L-arginine is the direct precursor of nitric oxide, while L-citrulline is indirectly involved in the process.

L-arginine and L-citrulline are both amino acids and very similar in their chemical structure and many other respects. 

Both are found in foods such as fish, dairy, eggs, and many supplements. So, you could choose a base diet with arginine content or look for a supplement. 

Both are used as dietary supplements to help with circulation, and heart health, among other applications.

In terms of health benefits, both L-arginine and L-citrulline have been shown to have beneficial effects on blood flow. 

Although L-arginine is more commonly used for these applications, L-citrulline can be used as an alternative.

Effectiveness

Studies have shown that supplementing with L-arginine can increase NO production and improve blood flow, but the effects are short-lived, and the absorption of L-arginine is not very efficient. 

Thus, it doesn’t reach very high plasma amino acid concentration. This could improve by giving higher doses of L-arginine, but such high doses could cause gastrointestinal distress.

Conversely, supplementing with L-citrulline can increase NO production and improve blood flow more effectively than L-arginine. 

Furthermore, L-citrulline is better absorbed than L-arginine and does not cause gastrointestinal distress. 

Therefore, L-citrulline is generally considered a more effective supplement for increasing NO production and improving cardiovascular health than L-arginine.

Also, L-citrulline is not broken down by the body like L-arginine is. That’s why it is thought to have better bioavailability than L-arginine, meaning that it is more likely to be absorbed and utilized by the body.

How long do they take to work?

After taking either L-arginine or L-citrulline, it only takes a few minutes or up to one hour before the supplements or nutrients in foods are absorbed and used in the organism. 

But the caveat of arginine or citrulline supplementation is that it takes longer to give noticeable results.

Nitric oxide production starts the same day you take the first pill. However, the effects of L-arginine and L-citrulline are not immediate. 

Depending on what effects you’re looking for, it could take a few weeks to a few months to take effect. 

For example, suppose you’re taking L- arginine or L-citrulline for erectile dysfunction. In that case, you might need to wait one month of continued use for it to take effect.

And remember that erectile dysfunction not only depends on nitric oxide, so if you’re not seeing results yet, you may need something else.

But suppose you’re taking L-citrulline to improve muscle performance. In that case, the effects will be more noticeable after seven days of taking it daily without missing one dose.

Which is better?

Both L-citrulline and L-arginine are excellent at increasing nitric oxide levels. They can be used together in the same supplements without a problem. 

However, if you have to choose between one of them, most studies would point out that L-citrulline is better.

L-citrulline has better bioavailability. It is absorbed faster and remains unchanged in the body for longer. 

In contrast, since L-arginine is more commonly recognized by many cells, they take L-arginine and convert it to something else before it turns into nitric oxide. 

This is known as first-pass metabolism. That does not happen with L-citrulline, which reaches the enzymes that convert it to L-arginine and then to nitric oxide without being modified by other cells and enzymes in the process.

But then, which one should I use? L-citrulline vs L-arginine for cardiovascular disease, erectile dysfunction, or bodybuilding? 

Both are fine if you are looking for long-term results, such as improving your cardiovascular disease. 

But if you want to see a very specific effect on your muscle function or erectile dysfunction, use a combination supplement of both or L-citrulline alone.

Should I take L-arginine and L-citrulline together?

As noted above, L-arginine and L-citrulline are two closely related amino acids that have been studied for their potential to increase nitric oxide (NO) levels in the body. 

Taking both of these amino acids together may further maximize the benefits of NO production, as each of these amino acids is a precursor for the synthesis of NO.

When taken together, L-arginine with L-citrulline can work synergistically in the body to increase NO production. 

L-arginine will produce nitric oxide directly, and L-citrulline will produce additional effects and increase the supplement’s bioavailability.

The combination can be beneficial for those looking to maximize nitric oxide production in the body. These amino acids can work synergistically to increase NO production, resulting in improved circulation, muscle growth, exercise performance, and overall health. 

Conclusion

In this review of L-citrulline vs L-arginine, we have seen they are amino acids involved in the formation of nitric oxide. 

This gas molecule is essential to control blood pressure, enhance immune function, and may even improve physical performance and erectile problems.

Arginine and citrulline supplementation increases plasma levels of these amino acids. They are used to create nitric oxide, which ultimately makes a difference in hypertension, erectile dysfunction, and other problems. 

Bodybuilders also use this type of essential amino acid supplement to increase their physical performance, measured by barbell bench press repetitions, walking distance, or maximum load.

One of the main differences between L-citrulline and L-arginine is that the latter is converted into other metabolites and waste products. 

Arginine degradation results in a decrease in plasma arginine concentration. This does not happen with citrulline, which reaches the cells untouched and has better bioavailability.

Thus, L-citrulline has more applications than L-arginine, but they can be used in combination for better results.

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