L-Citrulline has a close relationship with another amino acid. This second amino acid is known as arginine. While citrulline is a non-essential amino acid, arginine is normally categorized as a semi-essential amino acid. Sometimes arginine can be called a conditionally essential amino acid.
Being semi-essential means that while it is produced naturally by the body, (allowing it to play its role in the system) there are some cases where it is needed through diet or supplementation. For instance, a newborn would not produce enough of the amino acid that’s required. Therefore, it would need to be supplied in other ways, like diet and supplementation.
Arginine and citrulline are actually popular supplements, and while citrulline is converted to arginine through the kidneys, there are some benefits to taking l arginine and l citrulline together.
The main benefit involves nitric oxide. L arginine and l citrulline taken together creates an environment where nitric oxide can be formed efficiently, because of their roles in the nitric oxide pathway.
Arginine and Citrulline Benefits
The information in the previous section, regarding nitric oxide synthesis, lays the foundation for other specific benefits. This entire next segment will list out some of the perks of taking the two amino acids, l arginine and l citrulline, together.
Our hearts are one of the most critical organs that we have in the body. While the brain is the most important (and can’t be transplanted) because it controls the signals between body parts along with carrying our thoughts and memories, the heart will take the spotlight here because how the amino acids l arginine and citrulline work together to support it.
In a published research experiment from 2018, rabbits were given both arginine and citrulline to see its impact on the cardiovascular system. The rabbits were fed a high-cholesterol diet for 4 weeks, which induced atherosclerosis in them. This is the scientific term for clogged arteries.
Over the course of the 4 weeks, the study showed that after consuming l arginine and l citrulline, the rabbits :
- Had increased nitric oxide production in the plasma
- Slowed down senescence of the endothelial cells (senescence basically means aging or deterioration)
- Had a therapeutic response to the amino acid combination
How does this relate to humans? By looking at research carried out on animals, we can find a basis on how this would work on human beings. We don’t need to force feed ourselves a high-cholesterol diet per se, but we can still get some insight on how it may affect us.
Thankfully, studies have already been carried out regarding these amino acids, and their effects are established in the scientific community. Through science, we know that arginine and citrulline :
- Are precursors to nitric oxide (NO)
- Nitric oxide allows easier blood flow through vasodilation
- Nitric oxide has three forms (endothelial NO, neural NO, and inducive NO)
It just so happens that skeletal muscle uses all three different forms of nitric oxide. While this is important for general health purposes, this leads us to our next section, which is more specified.
Due to the fact that arginine, citrulline, and nitric oxide have essential parts in having healthy hearts, particularly through increased blood flow. It would make sense that it could be applied to a specific scenario – exercise!
Different studies have been carried out on athletes to help understand the efficacy of both citrulline and arginine when it comes to exercise. The findings were that, depending on the type of exercise, the benefits were :
- Higher levels of growth hormone and insulin in cyclists
- Lowered lactate plasma levels
- Reduced oxygen requirement and more efficient oxygen delivery
- Improved time until exhaustion in cardio activities
- Increased saturation of skeletal muscle oxygen in lifters
- Weightlifters were able to perform more repetitions
Oxygen is provided to the muscles through blood circulation, and when we examine the lifters, it was shown that they had an increased saturation of oxygen. This finding gives support to the notion that arginine and citrulline, along with their product, nitric oxide, improves blood flow which in turn allows for an easier delivery of oxygen and nutrients in the muscles.
Blood flow is one of the reasons why people warm up before undertaking any kind of exercise. It helps in the preparation of your skeletal muscle system so that you can perform any main movements during your exercise session.
Some symptoms of weak blood circulation can be coldness and stiffness in the muscle and joints. While you don’t necessarily need to have “weak” circulation, your muscles still may be tight, especially if you work a desk job with minimal movement. Warming up will supply the skeletal muscle areas with the blood flow that you need, and arginine and citrulline should help with this during warm-ups as well as throughout the workout.
Fatigue & Muscle Soreness
The previous section dealt with some of the benefits that l arginine and l citrulline can possibly bring before and during exercise. However, this one will discuss what happens after you do an exercise. There are studies out there that show the supplements possible benefits relating to muscle soreness and fatigue.
While this study doesn’t involve the ingestion of l arginine and l citrulline simultaneously, citrulline is the subject of the study. We know that citrulline is synthesized into arginine in the kidneys, and for all intents and purposes, still supports this particular benefit.
By taking a citrulline malate supplement, 41 men were asked to perform the flat, barbell bench press, which is one of the most popular weight training exercises out there. In this exercise, the men were required to perform a total of 16 sets at 80 percent of their one-rep maxes. This took two sessions.
The lifters were given citrulline malate in one of the two sessions, and a placebo was given in the other. This allowed the test administers to judge the efficacy of citrulline malate on muscle fatigue. The results showed that :
- After the third set was evaluated, the lifters were discovered to shown to have a “significant increase” of reps compared to placebo
- On average, around a 53 percent increase in reps was calculated between the participants
- 100 percent of the lifters showed a response to citrulline malate in the final set
Importantly, this study also showed some statistics regarding muscle soreness after working out. Following 24 to 48 hours of the bench press sessions the lifters had :
- A decrease of 40 percent in muscle soreness
- Approximately 90 percent response rate to citrulline malate and perceived muscle soreness
Since l-citrulline coverts to l-arginine, this information gives us an understanding of how these supplements can improve exercise performance by reducing fatigue, allowing for more reps or increased duration of exercise, along with a diminished case of delayed onset muscle soreness.
Arginine and Citrulline Dosage Information
Now that we know the main benefits of arginine and citrulline together, we can discuss the dosages of these amino acids. So how much l arginine and l citrulline do you need to take in order for it to be effective?
For heart functioning, a clinical trial showed that a dose as low as 2000 mg (2 grams) of l-arginine showed potential in healthy men by :
- Lowering blood sugar
- Reducing lipid profile
- Dropping LDL and HDL cholesterol levels
As usual, a placebo was also included in this trial of 52 healthy men, spanning 45 days. The placebo showed no results, but this low dose displayed a positive benefit in these men. The arginine dosages that pertain to fitness will be discussed next.
Arginine, as it concerns with exercise, has seen effectiveness in a 6-gram dose. In another trial, healthy men were placed on 6 grams of l-arginine during one session and given a placebo during another. The test was conducted by measuring an exercise involving a bicycle. The results for arginine versus the placebo were :
- Reduced required oxygen demand for the exercise
- Expended less energy
- Improved time to exhaustion by approximately 26 percent
Citrulline has shown effectiveness in dosages from as low as 2 grams.  You will probably notice that the typical citrulline supplement, especially citrulline malate, usually comes in servings of 2 to 3 grams. While there may be benefits by taking a higher dose, the studies are somewhat inconclusive. Sticking with the dose that’s provided on the label is more than likely enough to be effective, and importantly, safe.
You can also keep in mind that arginine and citrulline can be found in food sources as well. Citrulline is mostly known for coming from watermelon, which is where its name is derived from. Arginine rich foods can be bird meats such as turkey and chicken, along with dairy foods and certain seeds. This can provide another avenue in boosting your l arginine and l citrulline levels.
Why Do Arginine and Citrulline Make Great Pre-Workouts?
Based on the information throughout this article, l arginine and l citrulline taken together can be successful in improving your workout sessions. Here’s what we’ve learned about these amino acids regarding exercise:
- They can increase blood flow, allowing for efficient oxygen and nutrient supply
- Despite allowing for more oxygen retrieval, they can reduce the overall demand for oxygen in the muscle
- Less energy is used up when taking the amino acids
- They’ve shown reduced plasma lactate levels
- Reduced muscle soreness
Athletes, whether they perform aerobic exercises like cycling, or are into weight-training have seen results from l arginine and l citrulline in the various studies. For instance, cyclists have seen reduced time until exhaustion, and lifters were able to lift more reps on an exercise.
Since the benefits are seen during your exercise session, it makes more sense to take arginine and citrulline as your pre-workout. You’ll want the increased blood flow and other perks while you are doing intense exercise because it wouldn’t serve its intended purpose.
However, l arginine and l citrulline before bed could be beneficial too because these improvements can be great for overall health. Having a heart that functions well is important to your livelihood.
Taking these before you sleep should give you a steady source of prerequisites for nitric oxide. They don’t work like caffeine, and shouldn’t keep you awake either. In fact, they may be able to promote better sleep. Sleep apnea has been correlated with a state of diminished nitric oxide that circulates in the body .
Summary & Conclusion
In this article, we’ve learned a lot about the two amino acids and how they can provide tangible benefits to you. Arginine and citrulline have a relationship with one another; citrulline is converted to arginine which creates more nitric oxide flow. This doesn’t mean that one is more important than the other, however. Even though arginine comes directly before nitric oxide in the pathway, supplementing with citrulline will increase overall arginine concentration in the body.
With all of these increases of amino acid and nitric oxide concentrations, there’s a chance that you will experience the many benefits that were listed in the article. Overall, these benefits can be narrowed down to three areas. These are heart function, exercise performance, and muscle soreness.
These are all things that can improve your workout experience. Being able to last longer and pump out more reps is a good indicator of progress, and sometimes people need that little extra push to get there. By including arginine and citrulline supplements into your lifestyle you might see that improvement, just like how creatine is shown to give a slight edge.
Because the amino acids’ benefits are reflected during the workout, rather than after it, they make excellent candidates for a pre-workout combo. Combine arginine and citrulline together, and perhaps you will take your workouts to the next level, no matter what type of exercise you enjoy.
- Tsuboi, T., Maeda, M., & Hayashi, T. (2018). Administration of L-arginine plus L-citrulline or L-citrulline alone successfully retarded endothelial senescence. Plos One, 13(2). doi:10.1371/journal.pone.0192252
- Campbell, B. I., Bounty, P. M., & Roberts, M. (2004). The Ergogenic Potential of Arginine. Journal of the International Society of Sports Nutrition, 1(2), 35. doi:10.1186/1550-2783-1-2-35
- Willoughby, D. S. (2015). Intracellular Mechanistic Role Of Nitric Oxide: A Comparative Analysis Of The Effectiveness Of L-Arginine And L-Citrulline Supplementation On Nitric Oxide Synthesis And Subsequent Exercise Performance In Humans. International Journal of Food and Nutritional Science, 2(1), 1-8. doi:10.15436/2377-0619.15.010
- Pérez-Guisado, J., & Jakeman, P. M. (2010). Citrulline Malate Enhances Athletic Anaerobic Performance and Relieves Muscle Soreness. Journal of Strength and Conditioning Research, 24(5), 1215-1222. doi:10.1519/jsc.0b013e3181cb28e0
- Pahlavani, N., Jafari, M., Rezaei, M., Rasad, H., Sadeghi, O., Rahdar, H. A., & Entezari, M. H. (2014). L-arginine supplementation and risk factors of cardiovascular diseases in healthy men: A double-blind randomized clinical trial. F1000Research, 3, 306. doi:10.12688/f1000research.5877.1
- Bailey, S. J., Winyard, P. G., Vanhatalo, A., Blackwell, J. R., Dimenna, F. J., Wilkerson, D. P., & Jones, A. M. (2010). Acute l-arginine supplementation reduces the O2 cost of moderate- intensity exercise and enhances high-intensity exercise tolerance. Journal of Applied Physiology, 109(5), 1394-1403. doi:10.1152/japplphysiol.00503.2010
- 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
- Lavie, L., Hefetz, A., Luboshitzky, R., & Lavie, P. (2003). Plasma Levels of Nitric Oxide and L- Arginine in Sleep Apnea Patients: Effects of nCPAP Treatment. Journal of Molecular Neuroscience, 21(1), 57-64. doi:10.1385/jmn:21:1:57