Understanding the Science: What is the number one nitric oxide supplement?

October 3, 2025 •

4 min read

Nitric oxide plays a vital role in health, acting as a vasodilator to expand blood vessels for improved blood flow. Finding a definitive answer to the question, 'What is the number one nitric oxide supplement?' is complex, as the optimal choice depends on individual needs, biological responses, and ingredient efficacy.

Quick Summary

This article explores and compares the most effective ingredients for boosting nitric oxide, such as L-citrulline and beetroot, and explains why there is no single best supplement for everyone. It provides guidance on ingredient selection, product quality, and potential benefits for exercise performance and cardiovascular health.

Key Points

No Single 'Best' Supplement: The ideal nitric oxide supplement depends on your individual needs and how your body responds to different precursor ingredients.
L-Citrulline is Highly Effective: Due to superior absorption, L-citrulline is often considered more effective than L-arginine at raising blood nitric oxide levels over a sustained period.
Beetroot is a Natural Nitrate Source: High in dietary nitrates, beetroot extract is a potent, food-based method for boosting nitric oxide production, particularly beneficial for endurance.
Check for Quality and Third-Party Testing: To ensure purity and accurate dosing, always look for supplements that have been third-party tested by reputable organizations.
L-Arginine Has Limitations: The effectiveness of L-arginine is often hampered by poor bioavailability and digestive side effects at higher dosages.
Combining Precursors Can Maximize Effects: Some research suggests that combining L-citrulline and L-arginine may offer a synergistic boost to nitric oxide production.
Benefits Extend Beyond the Gym: Boosting nitric oxide can improve not just exercise performance but also cardiovascular health by promoting vasodilation and blood flow.

The Science of Nitric Oxide Production

Nitric oxide (NO) is a crucial signaling molecule in the human body, involved in blood vessel dilation, neurotransmission, and immune response. As we age, our natural NO production declines, prompting many to seek supplementation. However, no supplement contains nitric oxide directly. Instead, they provide precursors that the body converts into NO. The two primary pathways for NO production involve either amino acids like L-arginine and L-citrulline or dietary nitrates from vegetables like beetroot. Understanding these pathways is key to selecting an effective supplement.

L-Citrulline: The Bioavailability Advantage

L-citrulline is an amino acid that has gained prominence as a superior NO booster over L-arginine for several reasons. When ingested, L-citrulline bypasses the first-pass metabolism in the gut and liver, which breaks down a significant portion of L-arginine before it can enter the bloodstream. Instead, L-citrulline is efficiently converted to L-arginine in the kidneys, leading to higher and more sustained plasma L-arginine levels, and consequently, greater NO production. Research indicates that L-citrulline supplementation can lead to improved blood flow, enhanced exercise performance, and reduced muscle soreness. It is also generally better tolerated, with a lower risk of the gastrointestinal side effects sometimes associated with high doses of L-arginine.

L-Arginine: The Direct Precursor with Caveats

As a direct precursor to nitric oxide, L-arginine has long been a staple in NO supplements. However, its effectiveness is limited by poor absorption and significant breakdown in the liver and intestines. While the body uses L-arginine for NO synthesis, many other metabolic processes compete for this amino acid, limiting the amount available to boost NO levels. High doses, often necessary to overcome absorption issues, can lead to side effects such as nausea, diarrhea, and stomach pain. For these reasons, many experts now consider L-citrulline a more reliable and efficient method for increasing circulating L-arginine and boosting NO.

Beetroot: The Nitrate Pathway

Beetroot is a rich, natural source of dietary nitrates, which the body converts to nitric oxide through a different pathway that doesn't rely on L-arginine. This NOS-independent pathway is especially active in low-oxygen environments, making it beneficial for endurance athletes. Beetroot extract or powder has been shown to increase plasma nitrite levels, a marker for NO, leading to enhanced exercise tolerance and lower blood pressure. Products like HumanN SuperBeets are popular options utilizing this nitrate-rich approach. The best-quality beetroot supplements are often third-party tested and contain transparent labeling about their nitrate content.

How to Choose the Right Nitric Oxide Supplement

With a variety of products on the market, choosing the right NO supplement requires evaluating several factors beyond a simple 'number one' ranking. Consideration should be given to the ingredients, dosages, and third-party testing to ensure a quality and effective product.

Consider the Primary Ingredient: Decide if you prefer the amino acid-based approach (L-citrulline) or the nitrate-based approach (beetroot). L-citrulline is highly bioavailable for consistent NO elevation, while beetroot offers a natural source of nitrates.
Look for Optimal Dosages: Effective doses for L-citrulline typically range from 6 to 8 grams per day, while beetroot powder doses vary but should provide sufficient nitrate content. Check the label to ensure the product is not underdosed or uses proprietary blends that hide ingredient quantities.
Prioritize Third-Party Testing: To ensure purity and potency, look for supplements that have been independently verified by organizations such as NSF Certified for Sport or Informed Sport. This step is especially important for tested athletes.
Read Customer Reviews: While not a substitute for clinical research, customer feedback can offer insights into a product's effectiveness and potential side effects.

Comparison of Common Nitric Oxide Boosters


Feature	L-Citrulline	L-Arginine	Beetroot Extract
Mechanism	Converted to L-arginine in kidneys, bypassing breakdown.	Direct precursor to NO, but poorly absorbed.	Dietary nitrates convert to NO via oral bacteria and stomach acid.
Bioavailability	High; leads to more stable and elevated blood L-arginine.	Low; much is broken down before reaching circulation.	High; offers a reliable nitrate source for NO production.
Gastrointestinal Effects	Generally well-tolerated with fewer side effects.	High doses can cause stomach upset, nausea, or diarrhea.	Can have an earthy taste; some find it less palatable.
Best for	Sustained performance, pump, and recovery for athletes.	Cost-effective option for some users; best combined with L-citrulline.	Endurance sports and natural, food-based nitrate boosts.

Conclusion

While a singular "number one nitric oxide supplement" doesn't exist, scientific evidence points to L-citrulline as a highly effective and reliably absorbed option for boosting NO and enhancing performance. Nitrate-rich beetroot is another potent, natural alternative. The most prudent approach is to assess individual needs, prioritize products with proven ingredients at effective dosages, and verify third-party testing for quality assurance. By understanding the mechanisms behind these supplements and prioritizing product quality, consumers can make an informed decision to support their health and performance goals. Remember to consult a healthcare professional before beginning any new supplement regimen, especially if you have pre-existing health conditions or are on medication.

For more in-depth information, the National Institutes of Health (NIH) provides resources on nitric oxide synthesis and supplementation: https://pmc.ncbi.nlm.nih.gov/articles/PMC9710401/.

Frequently Asked Questions

L-citrulline is generally considered more effective at raising nitric oxide levels than L-arginine. This is because L-citrulline is better absorbed and converted into L-arginine in the kidneys, leading to higher and more sustained plasma L-arginine levels.

While certain foods like beetroot, leafy greens, and watermelon contain nitrates or citrulline that boost nitric oxide, it is difficult to consume the high dosages needed for performance-enhancing effects through diet alone.

Yes, beetroot supplements are a well-researched source of dietary nitrates, which the body converts into nitric oxide. Studies have shown they can improve blood flow, lower blood pressure, and enhance exercise performance.

Most people tolerate NO supplements well, but some may experience mild side effects, including gastrointestinal issues like upset stomach, nausea, or diarrhea, especially with high doses of L-arginine. Others may experience headaches or dizziness.

Nitric oxide acts as a vasodilator, meaning it relaxes and widens blood vessels. This can help improve blood flow and may lead to a modest reduction in blood pressure, especially in individuals with pre-existing hypertension.

Research shows mixed results, suggesting benefits are most prominent in untrained or moderately trained individuals rather than highly trained athletes. However, supplements containing L-citrulline or nitrates from beetroot can aid in blood flow, endurance, and muscle pumps for many.

Third-party testing involves an independent laboratory verifying a supplement's ingredients, potency, and freedom from contaminants. It is important because it provides an unbiased safety and quality assessment, offering consumers greater confidence in the product.