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L-Citrulline: Benefits, Dosage & Uses

L-Citrulline is a naturally occurring amino acid that plays a key role in the urea cycle and is widely used as a supplement to support circulation and athletic performance.

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Things worth knowing about "L-Citrulline"

L-Citrulline is a naturally occurring amino acid that plays a key role in the urea cycle and is widely used as a supplement to support circulation and athletic performance.

What is L-Citrulline?

L-Citrulline is a non-proteinogenic amino acid, meaning it is not used directly to build proteins in the body, but plays a vital role in metabolism. Its name is derived from the Latin word Citrullus (watermelon), as it was first isolated from watermelon. In the human body, L-Citrulline is produced mainly in the small intestinal mucosa and the liver, and serves as an important intermediate in the urea cycle.

Biological Functions

L-Citrulline fulfills several important functions in the human body:

Urea Cycle: L-Citrulline is a key intermediate in the process of converting toxic ammonia into urea, which is then excreted by the kidneys.
Nitric Oxide Production: L-Citrulline is converted in the kidneys to L-Arginine, which serves as a precursor for the synthesis of nitric oxide (NO). NO is an important signaling molecule that causes blood vessels to dilate and improves blood flow.
Amino Acid Metabolism: L-Citrulline supports the metabolism of other amino acids and contributes to the detoxification processes in the body.

Mechanism of Action

The primary mechanism of action of L-Citrulline is its conversion to L-Arginine in the kidneys. L-Arginine is the substrate for the enzyme nitric oxide synthase (NOS), which produces nitric oxide (NO). NO induces vasodilation (widening of blood vessels), leading to improved blood flow, lower blood pressure, and enhanced delivery of oxygen and nutrients to the muscles. Notably, L-Citrulline supplementation raises blood L-Arginine levels more effectively than direct L-Arginine supplementation, because L-Citrulline is more resistant to breakdown in the gastrointestinal tract.

Dietary Sources

L-Citrulline is naturally found in a variety of foods. Particularly rich sources include:

Watermelon (especially the rind and white flesh)
Pumpkin and other cucurbit vegetables
Cucumbers
Onions and garlic
Legumes such as chickpeas
Meat, especially liver

Medical Applications

L-Citrulline is used both in medicine and as a dietary supplement. Key areas of application include:

High Blood Pressure (Hypertension): By promoting NO production, L-Citrulline may help reduce blood pressure.
Erectile Dysfunction: Clinical studies suggest that L-Citrulline may have a supportive effect in mild to moderate erectile dysfunction through improved blood flow.
Athletic Performance: L-Citrulline is a popular supplement in sports nutrition, as it may enhance endurance performance, improve muscle recovery, and reduce muscle soreness.
Cardiovascular Disease: Due to its vasodilatory properties, L-Citrulline is being studied in the context of atherosclerosis and heart failure.
Urea Cycle Disorders: In rare inherited disorders of the urea cycle, L-Citrulline may be used therapeutically.

Dosage and Supplementation

As a dietary supplement, L-Citrulline is commonly available as L-Citrulline Malate (a compound with malic acid) or as pure L-Citrulline powder. Typical doses used in studies range from 3 to 6 grams per day, while for athletic performance enhancement, 6 to 8 grams of Citrulline Malate taken approximately 60 minutes before exercise is commonly used. L-Citrulline does not have drug approval in most countries and is primarily used as a supplement. Intake should always be discussed with a healthcare professional.

Side Effects and Safety

L-Citrulline is generally considered safe and well tolerated at recommended doses. Possible side effects are rare but may include:

Gastrointestinal discomfort such as nausea or diarrhea at high doses
Headaches (rare)
Drop in blood pressure, especially in combination with antihypertensive medications or erectile dysfunction drugs (e.g., PDE-5 inhibitors)

Individuals with kidney disease, severe liver failure, or known urea cycle disorders should only take L-Citrulline under medical supervision. Sufficient safety data for pregnant or breastfeeding women is currently lacking.

Interactions

L-Citrulline may interact with the following substances:

Antihypertensives (blood pressure-lowering medications): May amplify the blood pressure-lowering effect
PDE-5 inhibitors (e.g., sildenafil): Increased risk of a significant drop in blood pressure
L-Arginine: Combined use may further increase NO production, but should be medically supervised

References

Schwedhelm E. et al. - Pharmacokinetic and pharmacodynamic properties of oral L-citrulline and L-arginine. British Journal of Clinical Pharmacology, 65(1): 51-59 (2008).
Sureda A. et al. - L-citrulline malate influence over branched chain amino acid utilization during exercise. European Journal of Applied Physiology, 110(2): 341-351 (2010).
World Health Organization (WHO) - Amino acids in human nutrition. WHO Technical Report Series, Geneva.

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