L-Citrulline

L-Citrulline is a non-essential amino acid that plays a key role in the urea cycle, helping the body eliminate ammonia and recycle arginine. It is naturally found in watermelon and is produced industrially via fermentation for supplement use. Unlike arginine, L-Citrulline has superior oral bioavailability and is more effective at raising plasma arginine levels, making it a preferred precursor for nitric oxide synthesis.

Brands use L-Citrulline primarily in sports nutrition and performance products. Its ability to support nitric oxide production, improve blood flow, and reduce fatigue makes it a staple ingredient for endurance and recovery formulations. However, its effective dose range (3,000–10,000 mg) makes it impractical for gummy formats, and it is best delivered in sachet or powder formats.

Origin and history

L-Citrulline was first isolated from watermelon (Citrullus lanatus) in 1914 by Japanese researchers. Its name derives from the Latin word for watermelon, reflecting its natural abundance in the fruit. For decades, it remained a relatively obscure amino acid until research in the 1990s and 2000s revealed its role in the nitric oxide pathway and its superior bioavailability compared to arginine.

Today, L-Citrulline is produced industrially through bacterial fermentation using carbohydrates as feedstock. The fermentation process yields high-purity L-Citrulline that is suitable for food supplement applications. It is available as free-form L-Citrulline or as L-Citrulline DL-Malate, which combines citrulline with malic acid for potential additional energy benefits.

Scientific overview

L-Citrulline is a key intermediate in the urea cycle, where it helps convert ammonia into urea for excretion. More importantly for sports nutrition, it serves as a precursor to arginine, which is converted to nitric oxide via nitric oxide synthase. Nitric oxide is a vasodilator that improves blood flow, oxygen delivery, and nutrient transport to muscles during exercise. Unlike direct arginine supplementation, L-Citrulline bypasses first-pass metabolism in the liver and the intestinal arginase enzyme, resulting in more sustained and higher plasma arginine levels.

The bioavailability of L-Citrulline is excellent, with oral doses showing significant increases in plasma citrulline and arginine levels within 1–2 hours. The effective dose range for sports performance is typically 3,000–10,000 mg, with most studies using 6,000 mg as a standard dose. L-Citrulline DL-Malate is often used at similar doses and may offer additional benefits from malic acid in the ATP energy cycle.

From a manufacturing perspective, L-Citrulline is heat-stable and soluble in water, making it suitable for sachet and powder formats. However, its high effective dose makes it impractical for gummy formats, where payload constraints limit the amount of active per piece. The slightly bitter taste requires masking in ready-to-mix powders or sachets. Cost per mg is moderate, but the high dose means per-serving costs are significant.

L-Citrulline is one of the most familiar and commercially understood amino acids for sports performance across EU and US markets. Brands use it to position products around endurance, recovery, and nitric oxide support. However, its effective dose of 3,000–10,000 mg per serving makes it impractical for gummy formats, where a single gummy typically delivers 50–200 mg of active. A 6,000 mg dose would require 30–120 gummies per serving, which is commercially unviable.

For brands committed to gummy formats, L-Citrulline can be included at lower, sub-effective doses as part of a broader amino acid blend or combined with other nitric oxide precursors like arginine and beetroot extract. However, the primary delivery format for L-Citrulline remains sachets and powders. DAT can advise on the best format for your target dose and market positioning.

Pack copy for L-Citrulline should avoid disease claims and unauthorised structure-function language. In the EU, no specific health claims are authorised under Reg. (EU) 432/2012. Brands should position around general wellness, sports performance, or nitric oxide support without making specific health claims. DAT reviews claim wording per project to ensure compliance with local regulations.