Your Complete Guide To L-Citrulline Supplementation

Your Complete Guide To L-Citrulline Supplementation

L-citrulline belongs to a family called amino acids. All amino acids can be categorized into three different groups. These groups are known as non-essential, semi-essential, and essential. Before you start thinking that some of these aren’t important to you, let’s explain what the word essential means in this case.

When talking about amino acids, non-essential means that they are produced by the body naturally. However, supplementation of non-essential amino acids, such as l-citrulline, can provide the user some benefits, due to the fact that more of it is being used by the body. Despite being labeled as non-essential, it can prove to be essential for certain body functions. Let’s discuss more in-depth about l citrulline and what it can do for you.

What Is L Citrulline

What Is L Citrulline?

We’ve briefly started this article with some background about L-citrulline. We know that it’s a non-essential amino acid, but there are other things that you should know about citrulline. For example, did you know that its name comes from the Latin word, Citrullus? This is most likely because the genus Citrullus, or watermelon, is a great natural source containing a high amount of citrulline [1].

L Citrulline is an amino acid that enacts on the blood vessels and the heart. L-citrulline also has a crucial role in excreting ammonia from the body, which is toxic. The process is known as the urea cycle, and in the kidneys, citrulline has a function in converting ammonia into urea. Following this, it can be expelled during urination.

With this information about what l citrulline does in the body in natural circumstances, what happens when L-citrulline is provided through diet (such as eating watermelon or drinking its juice) or using a supplement specifically for citrulline? Research shows that supplementing with citrulline can have positive effects on the body. These l citrulline benefits are often related to:

  • improved vascular function
  • better exercise capacity

The Benefits of Citrulline 

Just a moment ago, we just mentioned a few possible perks to using a citrulline supplement. This section will be able to tell you more in detail about why citrulline can help these different bodily functions

 Increased Blood Flow

  1. Increased Blood Flow

When citrulline goes through the kidneys it transforms into another amino acid called arginine. To compare to citrulline, arginine is called a semi-essential amino acid. Arginine is also part of the process of nitric oxide biosynthesis [2].

When more citrulline is introduced into the user’s system, this allows for the creation of more arginine, which leads to more nitric oxide. Nitric oxide is able to expand a person’s blood vessels, and this allows more blood flow to reach all of your organs, especially the heart and brain. The event where blood vessels expand is known as vasodilation.

To measure increased blood flow, studies have usually involved exercise. This isn’t surprising, due to the fact that exercise increases heart rate and blood flow. It makes measuring practical. It’s also useful in seeing if a supplement has any benefit towards blood flow and exercise.

A study was carried out among 25 adults who were of an older age (between 60 to 80 years old). The sample size was quite even, consisting of 12 men and 13 women. This was a double-blind study, which means none of the participants knew who was receiving a supplement or not. A participant was either given 14 days of l citrulline or they were given a placebo, which was maltodextrin.

The participants were told not to consume any caffeine and vitamins or supplements for at least 8 hours prior to the testing. This makes sense because these other substances can also possibly raise blood flow, and the point of the study was to see the effects of l citrulline.  Using a calf exercise, the study produced some interesting results in regards to blood flow [3]:

  • Both groups showed an increase of 30 to 35 percent increase in plasma arginine following citrulline supplementation
  • The older men showed an increase of 11 percent in regards to femoral blood flow (involving the main artery in the leg)
  • The same older men displayed an increase of 14 percent in vascular conductance
  • No change was seen in the group of older women

As you would probably expect, none of the groups showed any changes when taking a placebo. However, the most interesting result here is the difference between men and women. Why did men show results but the women did not? The study mentions that muscle metabolism has a factor in this, and it suggests that older men most likely have a higher exercise tolerance than the older women [3]. Older individuals are often good candidates for similar types of studies because of vascular aging and decreased function in the arteries.

Because of increased blood flow, l-citrulline for ED has been a discussed topic. While few studies have been administered regarding this issue, therefore limited information, one study suggests that l citrulline can improve erection hardness in men who have mild cases of erectile dysfunction [7]. While this perk is exclusive to men, it’s just another possible benefit of citrulline.

Decreased Blood Pressure

  1. Decreased Blood Pressure

Blood pressure can be alarming at times, but luckily, it can be treated. L citrulline shows a lot of promise in treating higher blood pressure levels in those with hypertension and pre-hypertension. An overall reduction in blood pressure can minimize the burden it has on your heart, arteries, and veins.

On top of the results regarding blood flow, the study that was used in the previous section also showed some findings when it comes to blood pressure and citrulline [3].

  • The older men had reduced diastolic blood pressure by taking the citrulline supplement
  • The women showed no change

Once again, there was a difference in older men and women regarding these variables. This study suggests that because the men were taller, weighed more, and possessed higher BMI, this led to higher diastolic blood pressure compared to women. Because they had higher diastolic blood pressure overall, it’s possible that made them more responsive to the citrulline supplement.

Watermelon itself shows promise in having positive effects on blood pressure. A study was conducted by using a cold pressor test, which is an assessment that is used to measure heart rate and blood pressure changes by soaking the hands in ice-cold water for up to a minute.

The study involved 13 people, of which 10 were women. Over a course of 6 weeks, these individuals were given watermelon supplement or a placebo. It should be noted that all of these people were obese and suffering from hypertension. Here are the results [4]:

  • Compared to the placebo, the subjects who took watermelon supplementation showed a reduction in brachial systolic blood pressure and aortic systolic blood pressure
  • There was decreased augmentation pressure during the cold pressor test
  • The cold pressor test revealed that the demand for myocardial oxygen was reduced

Overall, this study supports the positive potential that l citrulline has on blood pressure. Since watermelon has a high concentration of citrulline, it is possible that it can help protect the heart and arteries by reducing blood pressure. Reduced blood pressure can lower the impact and stress that it has on the organ and its pathways.

Improved Exercise Performance and Capacity

  1. Improved Exercise Performance and Capacity

We briefly talked about exercise in the first benefit of the list. When we exercise, it increases the heart rate and the circulation of blood within our body. When this happens, the blood vessels are dilated, delivering oxygenated blood to your body, especially your muscles. If blood flow is weak, this can result in coldness, numbness, stiffness, and even pain in your appendages.

These issues aren’t comfortable, but if you exercise it should increase blood flow to the working areas. However, what happens to someone who doesn’t have poor blood circulation and decides to improve it through an l citrulline supplement? The following studies should give you some insight.

The first study involves endurance exercise. It goes over details that we have already learned, such as increased l-arginine from l-citrulline, increased nitric oxide synthesis, decreased blood pressure, and improved blood flow. It mentions that because of increased peripheral blood flow due to l-citrulline people have shown [2]:

  • Improved vascular function
  • Skeletal muscle oxidation betterment
  • Improved performance

If we want to understand this further, we can even take a look at mice. An experiment was conducted on mice involving a swimming exercise. One group of mice was given a citrulline supplement and the other was not. The researchers measured the time up until they were exhausted from swimming. The findings in the group that did take citrulline were [5]:

  • Reduced blood ammonia level
  • Lowered blood lactate in the muscle
  • Compared to the non-supplemented group, the mice who took l-citrulline had a much longer overall swimming time before exhaustion, due to these changes.

The final study involves l-citrulline and muscle soreness. Male runners who were given a watermelon drink that was fortified with l-citrulline ran a half-marathon. As usual, there were runners who were not given citrulline. As you would expect, the runners who did receive l citrulline showed [1]:

  • Lower plasma lactate
  • Reduced glucose
  • Higher l-arginine concentration

What’s important is the statistic that was measured 24 to 72 hours after the race. During this period, the racers were evaluated for muscle soreness and damage. It was discovered that the perception of muscle soreness was reduced in these runners as well as maintained the reduced plasma lactate following the race [1].

Muscle soreness is an indicator of rigorous exercise, especially in those who are not adapted to it. It is caused by the build-up of lactic acid in the muscle. While recovery should still be taken into account, the perception of soreness, or lack thereof, can potentially improve the endurance of athletes.

L-Citrulline Dosage

L-Citrulline Dosage

L-citrulline comes naturally from watermelons, but what is the effective L citrulline dosage for those who take oral supplements? A study points out that dosages that are anywhere from 2 grams to 15 grams are effective. However, citrulline concentrations in plasma were increased 100-fold with a 15-gram citrulline dosage, compared to 10-fold with a 2-gram dosage [6].

Dosage is something to consider when choosing a supplement. After all, you are spending money and you want it to work, right? One popular supplement form on the market is citrulline malate. This supplement is created by using citrulline and malic acid. L citrulline malate is a compound and is often in a powdered form. This allows the l citrulline powder to be mixed into water.

Upon comparing the serving sizes of different citrulline malate products, the typical dosages in these servings range from 2 to 3 grams. This falls in line with the study of this section. While it says that 10 grams showed higher citrulline concentration, it’s best to be on the safe side and follow the proper serving size and dosage of the product that you purchase.

Summary & Conclusion

Summary & Conclusion

To many people, watermelon tastes wonderful. What is even more wonderful is the potential l citrulline benefits, which comes from watermelon. While this amino acid is produced naturally in our bodies, these various studies show that l citrulline can have a positive effect on our bodies.

With increased blood flow, you will be able to provide your organs and muscles with an increased oxygen supply. This improved blood flow can have a benefit on athletes, and even in mice that swim! Not only that, having good blood circulation is just great for your general health and well-being. The same can be said for reducing blood pressure, which is another benefit of l-citrulline.

Many people who are researching l-citrulline are athletes who are interested in improving their performance in whichever sport they participate in. You can be a runner or a weightlifter, and still probably see some potential in l-citrulline. Despite being categorized as a non-essential amino acid, L-citrulline can be an essential part of your supplement stack if it works for you.


  1. Martínez-Sánchez, A., Ramos-Campo, D. J., Fernández-Lobato, B., Rubio-Arias, J. A., Alacid, , & Aguayo, E. (2017). Biochemical, physiological, and performance response of a     functional watermelon juice enriched in L-citrulline during a half-marathon race. Food          & Nutrition Research, 61(1), 1330098. doi:10.1080/16546628.2017.1330098
  1. Figueroa, A., Wong, A., Jaime, S. J., & Gonzales, J. U. (2017). Influence of L-citrulline and watermelon supplementation on vascular function and exercise performance. Current             Opinion in Clinical Nutrition and Metabolic Care, 20(1), 92-98.             doi:10.1097/mco.0000000000000340
  1. Gonzales, J. U., Raymond, A., Ashley, J., & Kim, Y. (2017). Does l-citrulline supplementation improve exercise blood flow in older adults? Experimental Physiology, 102(12), 1661-     doi:10.1113/ep086587
  2. Figueroa, A., Wong, A., & Kalfon, R. (2014). Effects of Watermelon Supplementation on Aortic Hemodynamic Responses to the Cold Pressor Test in Obese Hypertensive Adults. American Journal of Hypertension, 27(7), 899-906. doi:10.1093/ajh/hpt295
  1. Takeda, K., Machida, M., Kohara, A., Omi, N., & Takemasa, T. (2011). Effects of Citrulline Supplementation on Fatigue and Exercise Performance in Mice. Journal of Nutritional             Science and Vitaminology, 57(3), 246-250. doi:10.3177/jnsv.57.246
  1. Moinard, C., Nicolis, I., Neveux, N., Darquy, S., Bénazeth, S., & Cynober, L. (2007). Dose- ranging effects of citrulline administration on plasma amino acids and hormonal patterns in healthy subjects: The Citrudose pharmacokinetic study. British Journal of Nutrition,         99(04). doi:10.1017/s0007114507841110
  1. Shindel, A. (2011). Oral L-Citrulline Supplementation Improves Erection Hardness in Men With Mild Erectile Dysfunction. Yearbook of Urology, 2011, 169-170.     doi:10.1016/j.yuro.2011.04.002