If you have ever taken a pre-workout supplement, it probably contained an ingredient called Citrulline.

The name Citrulline comes from citrillus, the Latin name for watermelon, which is a natural source of Citrulline.

Other food sources include peanuts, soybeans and kidney beans.

It was discovered in 1930 and since then there has been an increasing amount of research demonstrating its benefits.

By the end of this article you will know exactly what Citrulline is, why people take it as a supplement, what the benefits are, whether there are any side effects and more.

Let’s dive in.

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What is citrulline?

Citrulline is a non-essential amino acid that  plays a vital role in many important biological processes in the body.

Amino acids are small molecules that are used to form proteins, which are the basic building blocks of the body.

One of the important processes citrulline is involved in is the urea cycle. The urea cycle is an important process which clears ammonia out of the body. Ammonia is a by-product of normal metabolism. However, ammonia can be harmful if it builds up in the body, which is why the urea cycle is vital to maintain health. Citrulline is one of three amino acids involved in the urea cycle, alongside L-arginine and L-ornithine.

In addition to its role in the urea cycle, citrulline is also important in the metabolism and regulation of nitric oxide. Nitric oxide is a compound which is beneficial for both cardiovascular health and exercise performance.

Citrulline is found in some foods but only in very small amounts, which is why it is popular as a supplement.

Citrulline supplements are in either powder or capsule form.


Why do people supplement with citrulline?

Citrulline is mainly taken to enhance exercise performance, which is why it is commonly found in pre-workout supplement formulas.

Some people also choose to supplement with Citrulline to improve cardiovascular health.

As you will find out, Citrulline has a much wider range of benefits beyond just cardiovascular health and exercise performance, which we will explore in the next section of this article.

What are the benefits of citrulline?

Citrulline is very well absorbed in the body and provides numerous benefits in terms of both health and exercise performance. The benefits include: improving blood circulation, decreasing blood pressure and its associated complications, improving exercise performance, boosting immunity, promoting healing and muscle recovery after exercise by reducing muscle soreness and helping to reduce fatigue.


Let’s look at each of these benefits in turn.

Improved blood circulation

Improving blood circulation allows more for oxygen and nutrients to flow throughout the body. Blood circulation is an important marker for cardiovascular health and influences exercise performance.

Research has shown that citrulline improves blood flow when compared to placebo. This was a result of citrulline increasing levels of nitric oxide in the blood. Citrulline is therefore particularly beneficial for those looking to improve blood circulation.


Decreased blood pressure

Blood pressure is also a marker of cardiovascular health. Studies have shown citrulline to be effective in decreasing blood pressure. This makes citrulline a particularly beneficial supplement for individuals looking to improve cardiovascular health.

Some people with high blood pressure also suffer with erectile dysfunction. Citrulline has been shown to improve symptoms of erectile dysfunction.

Citrulline is therefore effective in helping to reduce both high blood pressure and the associated complications.


Improving exercise capacity and performance

Citrulline has also been shown to boost exercise capacity, which is the amount of exercise an individual can tolerate before they fatigue.

In addition to boosting exercise capacity, citrulline has also been demonstrated to improve exercise performance for both cardiovascular exercise and weight training, as well as for both aerobic (low intensity) and anaerobic (high intensity) activity. Citrulline has also been shown to be effective in reducing muscle fatigue after exercise, helping to promote recovery.

This makes citrulline helpful for individuals engaging in both cardiovascular exercise and weight training at both high and low intensities.


Boosting immunity

Exercise creates oxidative stress in the body. This is a natural by-product of exercising but if not dealt with adequately by the body, it can damage the immune system and impair exercise recovery.

Reducing oxidative stress is therefore important to maintain healthy functioning of the immune system and to promote recovery from exercise.

Research has shown that citrulline helps to prime immune cells which are involved in dealing with this oxidative stress after exercise. This means that citrulline enhances your ability to recover after a workout.


Promoting healing and muscle recovery

Reducing muscle soreness is also an important part of exercise recovery. If your muscles are sore, you won’t be able to train as hard or as often.

Citrulline has been shown to significantly decrease muscle soreness at 24 hours and 48 hours after exercise. This means that citrulline is particularly beneficial for helping you to get back in the gym after a tough training session and put in a good workout.


Reducing fatigue

Experiencing muscle fatigue can also make it hard to keep training regularly and intensely.


Research has demonstrated citrulline to be effective in reducing feelings of fatigue. This occurs as a result of citrulline stimulating aerobic pathways in the body which contribute to energy production.


Citrulline is therefore particularly helpful for those experiencing fatigue or people looking to improve energy levels.



Other effects of citrulline

The evidence base for the benefits of citrulline is still growing. This means that there are some effects that have been observed but which need more research to determine the significance of them.

For example, citrulline has been shown in research to increase the levels of creatinine in the blood during exercise.

Creatinine is a breakdown product of creatine phosphate in muscle tissue and is usually produced at a fairly constant rate by the body, depending on the muscle mass of the individual.

Blood levels of creatinine, known as serum creatinine is an important indicator of kidney health because it demonstrates that that normal muscle metabolism is taking place. Citrulline may therefore improve the functioning of the kidneys.

Research has also shown citrulline to significantly increase levels of growth hormone compared with placebo after exercise.

Growth hormone is released naturally following exercise, particularly weight training. It is important for stimulating growth, cell reproduction and cell regeneration in the body. This means that it is important for muscle building as well as for bone and joint health.

Citrulline may therefore help to enhance the effects of exercise in terms of muscle building and maintaining the health of the bones and joints.


What is the clinically effective dosage of citrulline?

The clinically effective dose of a substance is the amount that produces the desired response or effects that have been found in research studies.

There are two main forms of citrulline that are available to buy as supplements. The doses are different for each type. The two types are L-citrulline and citrulline malate.

To supplement L-citrulline for cardiovascular health or to alleviate erectile dysfunction, you need to take 1g of L-citrulline, three times a day with meals, for a total daily dose of 3g.

To supplement for cardiovascular health with a citrulline malate supplement, you need to take take 1.76 g of citrulline malate for every 1 gram of citrulline you would normally take.

To supplement citrulline to enhance sports performance, you need to take 6-8g of citrulline malate or 3-5g L-citrulline about an hour before exercise.

Citrulline does not need to be taken with meals to obtain the benefits of the supplement.


What types of results should I expect from using citrulline?

If you’re excited about citrulline by now, I understand.

There aren’t many natural supplements that are have been shown in research to provide a wide variety of benefits for both exercise performance and physical health.

Having said that, like any supplement, it’s not a magic pill.

Remember that supplements don’t build great physiques. Dedication to proper training and nutrition does.

There are a number of benefits you can expect from taking citrulline:

  • Improved circulation
  • Lower blood pressure
  • Better exercise performance (both weight training and cardio workouts)
  • Reduced muscle soreness after exercise
  • Improved recovery from exercise
  • Reduced fatigue

Does Citrulline have any side effects?

Unlike most supplements, there have been no reported side effects of taking Citrulline since it was discovered in 1930, even at high doses.

Some other supplements with similar benefits, such as ornithine and arginine, can cause diarrhoea at high doses but up to 15g of citrulline does not seem to have this effect.

However, the supplement is known to interact with certain medications including: Nitrates taken for heart disease and medications for erectile dysfunction. Combining L-citrulline with those drugs may cause a dangerous drop in blood pressure.

It’s worth checking with your doctor if you are taking any other medications, are pregnant or breastfeeding before deciding to supplement with citrulline.


The best citrulline supplements

When choosing a citrulline supplement, it is important to remember that not all supplements are the same. Purchasing a high-quality citrulline supplement is essential in order to get the benefits discussed in this article.

There are two main forms of citrulline being used in supplements: L-citrulline and citrulline malate.

L-citrulline is the free-form version of the amino acid citrulline.

 Citrulline malate is the amino acid citrulline attached to a molecule of malic acid (malate). Malic acid is known to improve energy production and reduce fatigue, which makes this form particularly beneficial.

Research has shown that both L-citrulline and citrulline malate provide significant boosts to both exercise performance and cardiovascular health, when taken in sufficient doses.

It is very important that the supplement you are purchasing contains high enough dose in order to get the benefits discussed in this article.

Citrulline is found on its own as a supplement but is also often found in pre-workout supplements, along with other ingredients to boost exercise performance.

If you are purchasing a pre-workout supplement containing citrulline, you need to make sure that it does not contain a ‘proprietary blend’.

A proprietary blend is when several different ingredients are listed together under a single label. The weight of the entire blend is given but not the amounts of the individual ingredients.

The ingredients are listed in descending order by weight, with the first listed ingredient being present in the highest amount and the last ingredient being present in the lowest amount.

The problem is that the amounts of each can be wildly disproportionate to each other and you cannot be sure of the amounts of citrullline or other ingredients in the supplement that you are getting.

So if you see a pre-workout supplement which states it contains a proprietary blend, don’t buy it, it is not worth your money.

If a company isn’t willing to tell you exactly what is in their supplement, it’s because they don’t want you to know. Don’t support them by purchasing their supplements. Force them to change their ways.

Make sure that the supplement you are purchasing clearly lists the amount of citrulline found in the product, as well as the amounts of the other ingredients.

You want to make sure that the supplement contains a high dose of citrulline per serving. This will ensure that you are getting a sufficient dose to get the benefits you desire from taking the supplement.

It is also worth checking that the product does not contain any synthetic sweeteners, additives or fillers.


The bottom line on citrulline


Citrulline is becoming more popular as a supplement and for good reason.

Numerous studies have shown that it provides benefits for exercise performance, both for cardiovascular exercise and weight training. It also helps to reduce fatigue, enhance recovery from exercise and improves cardiovascular health.

Unlike most supplements, there are no reported side effects for citrulline, making it a safe supplement to take for the vast majority of people.

Citrulline isn’t a magic pill but as part of a well-planned nutrition and exercise programme, it can help you feel more energetic, have better workouts and keep your heart healthy.