How long does it take for your body to absorb L-citrulline? A nutrition diet deep dive

November 3, 2025 •

4 min read

Research indicates that peak plasma concentrations of L-citrulline can occur within just one hour of oral ingestion. Understanding how long does it take for your body to absorb L-citrulline is crucial for timing your supplementation and maximizing benefits for athletic performance and cardiovascular health.

Quick Summary

Peak plasma levels of L-citrulline typically occur within 60 to 120 minutes of consumption, followed by conversion to L-arginine to boost nitric oxide. Optimizing dosage and timing can enhance its effects on exercise and blood flow.

Key Points

Peak Absorption: Plasma concentrations of L-citrulline typically peak within 60 to 120 minutes after consumption, depending on the dosage and form.
Optimal Timing: For exercise benefits, consuming L-citrulline about 60 minutes before a workout is often recommended to maximize nitric oxide boost.
Conversion to Arginine: After absorption, L-citrulline is efficiently converted to L-arginine in the kidneys, leading to increased nitric oxide production.
Faster Bioavailability: Unlike L-arginine, L-citrulline bypasses liver metabolism, resulting in more reliable and sustained increases in plasma arginine levels.
Factors Influencing Speed: The absorption rate can be affected by the specific form of the supplement (e.g., L-citrulline vs. citrulline HCl) and whether it is taken with or without food.
Sustained Effects: Elevated L-citrulline levels can remain in the bloodstream for several hours, contributing to longer-lasting benefits for exercise and blood flow.

What is L-citrulline?

L-citrulline is a non-essential amino acid, which means the body can produce it, but it can also be consumed through food and supplements. Its name originates from citrullus, the Latin word for watermelon, a food source particularly rich in this compound. Unlike other amino acids, L-citrulline is not used directly for building protein. Instead, it plays a vital role in two key metabolic processes: the urea cycle, which helps the body get rid of harmful ammonia, and the production of nitric oxide (NO). The ability of L-citrulline to increase NO production is a major reason for its popularity in the health and fitness world. NO is a vasodilator, meaning it helps to relax and widen blood vessels, thereby improving blood flow throughout the body.

The absorption and metabolic journey of L-citrulline

When L-citrulline is ingested orally, its absorption begins in the small intestine. It then enters the bloodstream and travels to the kidneys, where a significant portion is converted into L-arginine. This is where L-citrulline has a distinct advantage over supplementing with L-arginine directly. While L-arginine is heavily metabolized by the liver, L-citrulline bypasses this process, leading to higher, more sustained levels of L-arginine in the plasma. This, in turn, boosts nitric oxide synthesis. The process is relatively quick, with peak plasma concentrations occurring between 60 and 120 minutes after ingestion for most oral supplements.

Key factors influencing L-citrulline absorption

Several factors can influence how quickly L-citrulline is absorbed and its effects are felt. The form of the supplement, dosage, and intake with or without food all play a role.

Form of Supplement: The most common forms are L-citrulline and citrulline malate. Some studies suggest that certain formulations, like citrulline HCl, might reach peak plasma levels faster than pure L-citrulline, although pure L-citrulline can still lead to higher overall concentrations. Citrulline malate, a combination with malic acid, may have additional benefits related to energy production.
Dosage: Dosage can influence plasma concentrations of L-citrulline.
Food Intake: Taking L-citrulline on an empty stomach is generally recommended for optimal absorption. This ensures the fastest possible assimilation without interference from other nutrients, which is especially important for pre-workout timing.

Comparison: L-citrulline vs. L-arginine


Feature	L-Citrulline	L-Arginine
Absorption Rate	Rapidly and efficiently absorbed through the intestinal wall.	Absorbed, but significant portion is metabolized by the liver before entering circulation.
Metabolic Pathway	Bypasses the liver, leading to higher plasma levels of L-arginine.	Undergoes extensive first-pass metabolism in the liver.
Peak Plasma Levels	Reaches peak concentration in the blood within 60–120 minutes.	Peak levels may be lower and less sustained due to hepatic metabolism.
Gastrointestinal Effects	Well-tolerated, even at doses, with minimal digestive issues.	High doses can cause gastrointestinal distress and discomfort.
Effectiveness	More effective at raising and sustaining plasma L-arginine and NO levels.	Less effective at raising plasma L-arginine due to extensive breakdown.

Benefits tied to L-citrulline absorption

The relatively quick absorption and subsequent metabolic conversion of L-citrulline have several positive implications for health and fitness:

Enhanced Exercise Performance: The increase in nitric oxide improves blood flow and oxygen delivery to muscles during exercise, enhancing endurance and reducing fatigue. Timing a dose approximately one hour before a workout aligns perfectly with the absorption timeline.
Faster Muscle Recovery: Better blood flow and nutrient delivery to muscles during and after exercise can help accelerate the recovery process and reduce delayed-onset muscle soreness.
Cardiovascular Health: By promoting vasodilation, L-citrulline may help lower blood pressure in individuals with elevated blood pressure. The long-term effects on cardiovascular function benefit from its sustained impact on NO levels. For more information on the therapeutic potential, a detailed review is available from the National Institutes of Health.
Mild Erectile Dysfunction Support: The mechanism of improved blood flow has also shown potential benefits for mild-to-moderate erectile dysfunction.

Incorporating L-citrulline into your nutrition diet

While supplements offer a concentrated dose, you can also increase your L-citrulline intake through dietary sources. The most prominent food source is watermelon, from which the amino acid gets its name. Other foods containing L-citrulline include other melons (like cantaloupe and casaba), cucumbers, squash, and pumpkins. For individuals with specific performance goals or certain health conditions, supplementation is often necessary to achieve therapeutic dosages.

Here are some practical tips for adding L-citrulline to your regimen:

For athletic performance, consider the timing of your L-citrulline intake to potentially align with your workout schedule.
For general cardiovascular health, regular intake may be beneficial. You might consider splitting the intake throughout the day.
If taking it for blood pressure support, monitor your levels, especially if also taking medication for hypertension, as L-citrulline may further lower blood pressure.
Consider combining it with other nutrients for synergistic effects. For example, some people combine it with L-arginine to further enhance NO production, although L-citrulline alone is often sufficient and avoids the gastrointestinal issues associated with high doses of L-arginine.

Conclusion

In summary, the absorption of L-citrulline is a rapid and efficient process, with peak plasma levels typically achieved within one to two hours of ingestion. This makes it an effective and reliable supplement for acutely increasing nitric oxide production, especially when taken pre-workout. Compared to L-arginine, its superior bioavailability and lack of side effects at high doses make it a preferred choice for enhancing athletic performance, aiding muscle recovery, and supporting cardiovascular health. Incorporating L-citrulline into a balanced nutrition diet, whether through foods like watermelon or targeted supplementation, can be a powerful strategy for optimizing your health and fitness goals.

Frequently Asked Questions

L-citrulline is a non-essential amino acid that is not used to build proteins but is crucial for the body's urea cycle to eliminate ammonia and for producing nitric oxide, which helps dilate blood vessels.

After absorption, L-citrulline is primarily converted to L-arginine in the kidneys. This L-arginine then serves as a precursor for nitric oxide, a compound that relaxes blood vessels and improves circulation.

Yes, L-citrulline is generally more effective at increasing and sustaining plasma L-arginine levels than taking L-arginine directly. This is because it bypasses liver metabolism, which breaks down a significant portion of L-arginine before it can reach the bloodstream.

The main benefits include improved exercise performance and endurance, faster muscle recovery, support for cardiovascular health by lowering blood pressure, and potential improvements for mild erectile dysfunction.

For exercise benefits, it is best to take L-citrulline about 30 to 60 minutes before your workout to allow enough time for absorption and conversion to nitric oxide. Taking it on an empty stomach may speed up absorption.

Yes, watermelon is a primary food source of L-citrulline. It is also found in other fruits and vegetables like cucumbers, cantaloupe, and squash. However, obtaining therapeutic amounts for performance benefits usually requires supplementation.

L-citrulline is generally well-tolerated, even at doses. Some individuals may experience mild gastrointestinal discomfort. It is important to monitor blood pressure, especially if taking blood pressure medication, as L-citrulline can have a lowering effect.