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L-arginine and L-citrulline are two popular sports and health supplements. Both compounds play important roles in the body’s production of nitric oxide, a key signaling molecule involved in vasodilation, immune function, and other processes. With so many overlapping benefits, should you take L-arginine or L-citrulline? This comprehensive guide examines the differences, advantages, dosage considerations, safety issues, and overall value of each to help determine which comes out on top.

L-Arginine Overview

L-arginine is a semi-essential amino acid produced in small amounts by the body and obtained in the diet via high-protein foods. As a readily available supplement, L-arginine has been used to enhance athletic performance, improve vascular function, and support cardiovascular health. Its primary mechanism of action involves increasing nitric oxide levels.

Purported Benefits of L-Arginine

1. Boosts Nitric Oxide Levels: L-arginine gets converted into nitric oxide in vessel walls through an enzymatic process. Higher nitric oxide dilates blood vessels to enhance circulation.
2. Increases Growth Hormone Levels: By blocking somatostatin, L-arginine prompts the pituitary gland to secrete more growth hormone. This anabolic hormone builds muscle mass.
3. Aids Immune Function: The increased production of nitric oxide regulates immune cell response and fights inflammation from injury or infection. This helps improve immune defenses long-term.
4. Enhances Physical Performance: Widened blood vessels allow more oxygen and nutrients to reach working muscles. This nutrient delivery fuels performance. The release of growth hormone also builds more muscle over time.
5. Improves Heart Health: Opening up constricted arteries enables better heart function and blood flow. This also lowers blood pressure levels. Over time, the vascular support promotes healthy circulation and heart health.

L-Citrulline Overview

Though not a proteinogenic amino acid incorporated into muscle, L-citrulline plays a key role in cellular energy production and nitric oxide metabolism. It gets produced naturally in the body to some degree and has recently gained traction as an exercise and health supplement due to its nitric oxide upregulating effects.

Purported Benefits of L-Citrulline

1. Increases Nitric Oxide Through Multiple Pathways: Unlike L-arginine which directly converts, L-citrulline stimulates nitric oxide synthesis while also regenerating L-arginine stores for additional production. It jumpstarts the entire nitric oxide cycle in blood vessels.
2. Boosts ATP Energy Production: By removing nitrogen waste products in cells, L-citrulline facilitates continued ATP energy regeneration. This powers intense muscular contractions.
3. Reduces Lactic Acid Build-Up: Ammonia waste removal also reduces acidosis and burns, allowing for faster recovery between sets or athletic events. This supports more intense training with less pain.
4. Improves Blood Flow and Oxygen Circulation: Through sizable nitric oxide increases, L-citrulline significantly widens blood vessels to enhance circulation efficiency. More oxygen reaches working tissues.
5. Lowers Blood Pressure: The vasodilatory action of enhanced nitric oxide levels also relaxes artery walls. This lowers overall vascular resistance and, in turn, reduces blood pressure values.

L-Arginine vs. L-Citrulline: Key Differences

1. Now that the basics of both supplements are covered, here is a direct side-by-side comparison of some of their major differences:
2. Absorption and Bioavailability: Due to extensive first-pass metabolism, over 50% of L-arginine gets broken down by the liver before utilization. This hampers bioavailability. L-citrulline avoids this fate and gets fully absorbed for 100% bioavailability.
3. Nitric Oxide Conversion Rate: Only about 5-15% of L-arginine gets converted into nitric oxide because the reaction depends on a rate-limited enzyme. L-citrulline again has the advantage since every dose reliably elevates nitric oxide.
4. Onset Time: L-citrulline also activates nitric oxide faster, with blood levels peaking in 60 minutes. L-arginine is less direct with a 90-120 minute wait. This quicker action benefits athletes.
5. Magnitude of Effects: Via multiple pathways, L-citrulline causes double the peak nitric oxide levels compared to L-arginine. It also regenerates arginine stores. The robust effects are another check in L-citrulline’s column.
6. Professional Recommendations: Due to the more extensive benefits listed above, most sports dietitians and physicians specializing in nutrition now recommend L-citrulline over L-arginine. The collective evidence favors L-citrulline for effects on nitric oxide-related outcomes.

L-Citrulline vs. L-Arginine Dosage Considerations

The typical daily dosage recommendations also showcase some critical differences:

• L-Arginine Dosage: Research on L-arginine supports dosages between 3,000-6,000 mg taken in multiple smaller doses spread throughout the day. This compensates for the shorter window of elevated nitric oxide. Dividing the doses enhances absorption.
• L-Citrulline Dosage: In contrast, just one larger 3,000-6,000 mg dose taken 60 minutes before activity or other benefit is sought maximizes L-citrulline’s effectiveness. The quicker action and reliable bioavailability enable simpler, less frequent dosing.

For comparison, most studies showing athletic performance benefits use 6,000 mg of L-citrulline one hour pre-workout versus lower L-arginine doses multiple times daily. This reinforces L-citrulline as more efficient.

L-Citrulline Safety Considerations

While generally safe when manufacturers’ recommended dosages are followed, there are some potential side effects to consider with L-citrulline supplementation:

1. Gastrointestinal distress – Since it increases urea production, high doses can cause diarrhea, nausea, or stomach pain in sensitive users.
2. Hypoglycemia – By stimulating insulin release, L-citrulline can dangerously lower blood sugar in diabetic patients on medications.
3. Drug interactions – The nitric oxide elevating effects also pose problems for those taking nitrates for heart conditions or phosphodiesterase inhibitors for erectile dysfunction.

Doctors suggest those with kidney disease, liver cirrhosis, diabetes, or taking interacting meds avoid L-citrulline due to complications. Healthy individuals just need to moderate doses based on personal tolerance. Minor issues typically resolve quickly after stopping use.

L-Arginine Safety Considerations

L-arginine also comes with some safety cautions, particularly at higher doses:

1. Gastrointestinal issues – Like L-citrulline, abdominal bloating, diarrhea, and nausea are common L-arginine side effects.
2. Herpes flare-ups – Increased arginine levels can activate dormant herpes viruses, causing painful outbreaks. Those with herpes should avoid use.
3. Blood pressure concerns – Sudden vasodilation from high doses too quickly can precipitate hazardous blood pressure drops. This causes dizziness and fainting injury risks. Doctors recommend those with existing hypotension not use L-arginine supplements.

Starting with conservative doses and ramping slowly reduces adverse reactions. Consulting a doctor guides appropriate arginine use for individual health status as well.

Supplement Formulation Considerations

Thanks to expanding consumer demand, L-arginine and L-citrulline now come formulated in various supplement combinations:

Standalone L-Citrulline or L-Arginine

Isolated L-citrulline or L-arginine as sole active ingredients allows users to dictate the exact dosage of each. This works for targeting specific effects.

1. L-Citrulline with Malate or Aspartate: Malate and aspartate help stabilize absorption and extend citrulline activity time in the body. These compounds further boost workout capacity and recovery.
2. Pre-Workouts with L-Citrulline or L-Arginine: Many pre-workout blends contain moderate doses of both L-citrulline and L-arginine to maximize nitric oxide production pathways. This aims to increase power output potential.
3. Nitric Oxide Boosters: Some sports supplements specifically pack bigger L-citrulline or L-arginine doses with vitamin C, antioxidants, and botanicals to amplify nitric oxide levels even further. This rapidly widens blood vessels.

Of all the formulations, combinations with L-citrulline tend to offer the fastest and most robust effects. L-citrulline with malate or aspartate and workout blends boost physical performance better than standalone L-arginine too.

How is L-Citrulline better than L-Arginine?

When all factors are weighed, current research suggests L-citrulline offers more advantages as an exercise and health supplement compared to the once-popular L-arginine. Thanks to superior bioavailability, multiple nitric oxide elevating pathways, quicker action, and larger magnitude response, L-citrulline simply outperforms L-arginine. The collective evidence shows it activates muscle pumps faster for better workouts and recovers oxygen debt faster too. L-citrulline is also professionally recommended over L-arginine. With proper precautions for pre-existing health conditions, L-citrulline can safely enhance athletic training, lower blood pressure, improve circulation deficiencies like erectile dysfunction, and support heart health. When choosing a nitric oxide-boosting supplement, L-citrulline is the way to go.