Nitric oxide (NO) is a signalling molecule produced naturally in your blood vessels. It tells smooth muscle cells to relax, widening arteries and increasing blood flow. This single mechanism underpins cardiovascular health, exercise performance, blood pressure regulation, and — something most men over 40 care about — erectile function. Sildenafil (Viagra) works by protecting NO from being broken down. The question is whether you can boost NO production naturally through supplements.
The short answer: yes, with caveats. L-arginine is the direct amino acid precursor to nitric oxide, and it's supported by a meta-analysis showing significant blood pressure reductions. L-citrulline may actually be more effective at raising blood arginine levels because it bypasses first-pass liver metabolism. This guide covers the science behind both, how they compare, the doses that work, and how antioxidants like shilajit and vitamin C protect NO from degradation.
- L-Arginine is the direct precursor to nitric oxide via the enzyme nitric oxide synthase (NOS)
- A meta-analysis found L-arginine supplementation significantly reduced systolic blood pressure by 5.39 mmHg and diastolic by 2.66 mmHg (Dong et al., Am Heart J, 2011)
- L-Citrulline bypasses liver metabolism — oral citrulline raises plasma arginine more effectively than oral arginine itself (Schwedhelm et al., 2008)
- Antioxidants (vitamin C, shilajit) protect NO from oxidative degradation by scavenging superoxide radicals
- Blue Power contains L-Arginine 50mg + Shilajit 50mg — L-Arginine is the amino acid the body uses as a substrate for nitric oxide synthesis; Shilajit is a source of fulvic acid with antioxidant properties
| Study | Design | Finding | Funding |
|---|---|---|---|
| Dong et al. (2011) | Meta-analysis, 11 RCTs | L-Arginine reduced SBP −5.39 mmHg, DBP −2.66 mmHg | Independent |
| Schwedhelm et al. (2008) | Pharmacokinetic RCT | Citrulline raises plasma arginine more effectively than oral arginine | Independent |
| Allerton et al. (2018) | Systematic review & meta-analysis | L-Citrulline: significant FMD improvement, blood pressure reduction | Independent |
| Stanislavov & Nikolova (2003) | RCT, 3-month trial | L-Arginine + Pycnogenol: 92.5% normal erections at 3 months | Independent |
| Taddei et al. (1998) | Interventional study | Vitamin C improves endothelium-dependent vasodilation | Independent |
How Nitric Oxide Works: The Blood Flow Mechanism
The nitric oxide pathway is one of the most well-understood mechanisms in vascular biology. The 1998 Nobel Prize in Physiology or Medicine was awarded to Furchgott, Ignarro, and Murad specifically for discovering NO's role as a signalling molecule in the cardiovascular system. Here's how it works:
- L-Arginine (an amino acid) enters endothelial cells lining your blood vessels
- The enzyme nitric oxide synthase (eNOS) converts L-arginine into nitric oxide (NO) and L-citrulline
- NO diffuses into adjacent smooth muscle cells
- NO activates guanylate cyclase, which produces cyclic GMP (cGMP)
- cGMP causes smooth muscle to relax, widening the blood vessel (vasodilation)
- The enzyme PDE5 breaks down cGMP, ending the signal
L-Arginine vs L-Citrulline: Which Is the Better NO Supplement?
This is the most important question in nitric oxide supplementation, and the answer might surprise you.
L-Arginine: The Direct Precursor Most Studied
L-arginine is a semi-essential amino acid and the direct substrate for nitric oxide synthase. It's the most studied NO precursor with decades of clinical research. A meta-analysis of 11 randomised, double-blind, placebo-controlled trials found that oral L-arginine supplementation significantly reduced systolic blood pressure by 5.39 mmHg (95% CI: -8.54 to -2.25, P=0.001) and diastolic blood pressure by 2.66 mmHg (95% CI: -3.77 to -1.54, P<0.001) (Dong et al., Am Heart J, 2011).
The limitation? When you swallow L-arginine, approximately 40% is broken down by arginase enzymes in the gut and liver before it reaches systemic circulation — this is called first-pass metabolism. This means the dose on the label doesn't reflect how much actually reaches your blood vessels.
L-Citrulline: The Bypass Route
L-citrulline is a non-essential amino acid (found naturally in watermelon) that's converted to L-arginine in the kidneys — crucially, bypassing liver first-pass metabolism. A pharmacokinetic study found that oral L-citrulline supplementation was significantly more effective at raising plasma L-arginine levels than the same dose of oral L-arginine (Schwedhelm et al., Br J Clin Pharmacol, 2008).
A systematic review and meta-analysis of L-citrulline found significant improvements in flow-mediated dilation (FMD) — the gold-standard measure of endothelial function — and reductions in blood pressure, particularly in hypertensive populations (Allerton et al., Nutrients, 2018).
Head-to-Head Comparison
| Factor | L-Arginine | L-Citrulline |
|---|---|---|
| Mechanism | Direct substrate for eNOS | Converted to arginine in kidneys |
| Oral bioavailability | ~60% (40% lost to first-pass) | Higher — bypasses hepatic arginase |
| Plasma arginine increase | Moderate | Superior (Schwedhelm 2008) Better |
| Blood pressure evidence | Meta-analysis: -5.39/-2.66 mmHg | Meta-analysis: significant FMD improvement |
| Clinical study volume | Larger evidence base More studied | Growing but smaller |
| Typical study dose | 3–6g/day | 3–6g/day (or 1.5–3g citrulline malate) |
| In multi-ingredient formulas | 50–500mg as supporting dose | Less common in combination formulas |
Nitric Oxide and Erectile Function
The connection between nitric oxide and erectile function is not speculative — it's the foundational mechanism that every pharmaceutical ED treatment is built on. Erections are vascular events: NO released from nerve endings and endothelial cells in the penis activates the cGMP pathway, relaxing smooth muscle and allowing blood to fill the corpus cavernosum.
Men over 40 experience a natural decline in endothelial function and NO production. This is why age-related cardiovascular changes and erectile changes often track together — they share the same underlying mechanism. L-arginine is the amino-acid substrate the body uses in nitric oxide synthesis.
A study of L-arginine combined with Pycnogenol (pine bark extract) found that 92.5% of men experienced normal erections after 3 months of treatment, compared to 5% with L-arginine alone in month 1. The combination appeared to work synergistically, with the antioxidant properties of Pycnogenol protecting NO from oxidative degradation (Stanislavov & Nikolova, J Sex Marital Ther, 2003).
“The nitric oxide pathway is one of the most well-understood mechanisms in cardiovascular pharmacology — the 1998 Nobel Prize was awarded specifically for its discovery. What clinical trials confirm is that L-arginine at gram-level doses produces statistically significant blood pressure reductions, and that combining L-arginine with antioxidants dramatically amplifies its effect on erectile function. The mechanism is real; the question is always dose and context.”— Summarised from Dong et al. (2011), meta-analysis of 11 RCTs, American Heart Journal — L-arginine supplementation produced significant systolic (−5.39 mmHg) and diastolic (−2.66 mmHg) blood pressure reductions across controlled trials
Why Antioxidants Matter for Nitric Oxide
Producing nitric oxide is only half the equation. NO is rapidly destroyed by superoxide radicals — reactive oxygen species (ROS) that react with NO to form peroxynitrite (ONOO-), which not only eliminates NO but actively damages blood vessel walls. This is why antioxidants play a critical role in any NO-supporting strategy.
Vitamin C and NO Protection
Vitamin C (ascorbic acid) scavenges superoxide radicals before they can react with NO, effectively extending the lifespan of nitric oxide in your bloodstream. Studies have shown that vitamin C improves endothelium-dependent vasodilation in patients with coronary artery disease, hypertension, and diabetes — conditions characterised by increased oxidative stress and reduced NO bioavailability (Taddei et al., Circulation, 1998).
Shilajit and Vascular Antioxidant Support
Shilajit's fulvic acid increases glutathione (GSH), superoxide dismutase (SOD), and catalase activity in cardiac tissue, while decreasing lipid peroxidation — reducing oxidative stress in blood vessel walls (Winkler & Ghosh, 2018). By enhancing the antioxidant environment in which NO operates, shilajit may help protect newly produced NO from premature degradation. This is why formulators pair L-arginine with shilajit — one produces the signal, the other protects it.
Other Ways to Boost Nitric Oxide Naturally
Dietary Nitrate (Beetroot Juice)
There's a completely separate pathway for NO production that doesn't involve L-arginine at all. Dietary nitrate — found in beetroot, spinach, and rocket — is converted by bacteria on your tongue into nitrite, which is then further reduced to nitric oxide in acidic environments (like your stomach). A landmark study found that beetroot juice reduced systolic blood pressure by ~4–5 mmHg and improved exercise tolerance by 16% in healthy adults (Hoon et al., J Acad Nutr Diet, 2013).
Exercise
Physical exercise is the most potent natural stimulator of endothelial NO production. The shear stress of blood flowing past vessel walls during exercise upregulates eNOS expression and activity. Regular aerobic exercise has been shown to improve endothelial function and NO bioavailability even in men with cardiovascular risk factors. This is why exercise and NO supplementation work synergistically — supplements provide the raw material, exercise turns on the enzyme.
Nitric Oxide Supplement Dosage Guide
| Supplement | Clinical Dose Range | Multi-Ingredient Dose | Best For |
|---|---|---|---|
| L-Arginine | 3–6g/day | 50–500mg (supportive) | Blood pressure, general blood flow |
| L-Citrulline | 3–6g/day | 1–3g | Exercise performance, NO bioavailability |
| Citrulline Malate | 6–8g/day | 3–4g | Exercise endurance (2:1 citrulline:malate) |
| Beetroot extract/juice | 300–500mg nitrate/day | N/A | Alternative NO pathway via dietary nitrate |
- Blood pressure medication: L-arginine and L-citrulline can lower blood pressure — additive effects with antihypertensives. Consult your GP
- Blood thinners: Potential interaction with anticoagulant therapy
- Post-heart attack: L-arginine should be avoided in the acute phase after myocardial infarction (JAMA 2006 trial showed worse outcomes)
- PDE5 inhibitors: Combining NO boosters with Viagra/Cialis may cause excessive blood pressure drops
- GI tolerance: High doses of L-arginine (>6g) may cause gastrointestinal discomfort
Blue Power: L-Arginine 50mg + Shilajit 50mg
Blue Power provides L-Arginine 50mg alongside Shilajit 50mg and Vitamin C 80mg as part of a men's daily formula.
- L-Arginine: An amino acid that serves as the substrate for endothelial nitric oxide synthase (eNOS) in the body's own biochemistry
- Shilajit: A source of fulvic acid; research shows fulvic acid has antioxidant properties and may increase glutathione (GSH), SOD, and catalase activity (Winkler & Ghosh, 2018)
- Vitamin C 80mg: Vitamin C contributes to normal energy-yielding metabolism. Vitamin C contributes to the reduction of tiredness and fatigue.
Full formula: Shilajit 50mg · Tongkat Ali 50mg · Maca Root 50mg · Korean Ginseng 5:1 100mg · L-Arginine 50mg · Zinc 10mg · Horny Goat Weed 25mg · Vitamin C 80mg
Try Blue Power — L-Arginine + Shilajit in a Men's Daily Formula
One daily tablet. L-Arginine, Shilajit and Vitamin C alongside zinc and other ingredients. GMP certified, UK made.
Get Blue Power — Free UK DeliveryNo subscription required · 30-day supply · Free standard UK delivery
Frequently Asked Questions
What is the best nitric oxide supplement?
The best NO supplement depends on your goal. L-arginine is the most studied NO precursor, with a meta-analysis showing significant blood pressure reductions (-5.39 mmHg systolic). L-citrulline may be more bioavailable because it bypasses liver metabolism. L-arginine is the amino-acid substrate the body uses in nitric oxide synthesis, while antioxidants such as vitamin C are studied for general antioxidant activity. Choice depends on individual goals.
Is L-arginine or L-citrulline better for nitric oxide?
L-citrulline raises plasma arginine levels more effectively than oral L-arginine because it bypasses first-pass liver metabolism (Schwedhelm et al., 2008). However, L-arginine has a larger clinical evidence base including a meta-analysis of 11 RCTs. For standalone supplementation at high doses, L-citrulline may have an edge. In multi-ingredient formulas, L-arginine provides direct substrate support alongside synergistic compounds.
Does nitric oxide help with erectile function?
Nitric oxide is the fundamental mechanism behind erections. NO released in penile blood vessels activates cGMP, which relaxes smooth muscle and allows blood flow. Every pharmaceutical ED drug (Viagra, Cialis) works by protecting this NO signal from breakdown. For diagnosed ED, always consult your GP.
How much L-arginine should men take?
Clinical studies used 3–6g/day of standalone L-arginine for blood pressure and vascular function effects. Multi-ingredient formulas typically include 50–500mg as a supporting dose alongside other ingredients. High doses above 6g/day may cause gastrointestinal discomfort.
Can you boost nitric oxide naturally?
Yes — through three main routes: (1) L-arginine or L-citrulline supplementation, which provides the substrate for NO synthesis; (2) dietary nitrate from beetroot, spinach, and rocket, which follows a separate NO production pathway via oral bacteria; (3) regular aerobic exercise, which upregulates eNOS expression through blood flow shear stress. Combining all three is the most effective approach.
Are nitric oxide supplements safe?
L-arginine and L-citrulline are generally well-tolerated at standard supplement doses. Key precautions: do not combine with blood pressure medication or PDE5 inhibitors (Viagra, Cialis) without medical guidance, as the blood-pressure-lowering effects may be additive. Avoid L-arginine in the acute phase after a heart attack. High doses may cause GI discomfort. Always consult your GP if you take prescription medication.
The Bottom Line
Nitric oxide is the master regulator of blood flow in men — underpinning cardiovascular health, exercise performance, and erectile function through a single, well-understood mechanism. L-arginine is the direct precursor with a meta-analysis confirming blood pressure benefits. L-citrulline offers better oral bioavailability. And antioxidants — vitamin C and shilajit — protect the NO you produce from being destroyed by oxidative stress.
Blue Power provides L-arginine, shilajit, vitamin C and zinc as part of a men's daily formula. Vitamin C contributes to normal energy-yielding metabolism. Vitamin C contributes to the reduction of tiredness and fatigue. Zinc contributes to the maintenance of normal testosterone levels in the blood. For the full picture of what works for men in midlife, see our best supplements for men over 40 guide.
Explore further: Shilajit UK Benefits Guide · Tongkat Ali UK Guide · Best Supplements for Men Over 40
Related Reading
References & Sources (expand)
- Dong JY et al. (2011). Effect of oral L-arginine supplementation on blood pressure: a meta-analysis of randomized, double-blind, placebo-controlled trials. Am Heart J. PubMed 21310306
- Schwedhelm E et al. (2008). Pharmacokinetic and pharmacodynamic properties of oral L-citrulline and L-arginine. Br J Clin Pharmacol. PubMed 17214596
- Allerton TD et al. (2018). L-Citrulline Supplementation: Impact on Cardiometabolic Health. Nutrients. PubMed 28083742
- Stanislavov R & Nikolova V (2003). Treatment of erectile dysfunction with Pycnogenol and L-arginine. J Sex Marital Ther. PubMed 12851125
- Taddei S et al. (1998). Vitamin C Improves Endothelium-Dependent Vasodilation. Circulation. PubMed 10525231
- Winkler J & Ghosh S (2018). Therapeutic Potential of Fulvic Acid in Chronic Inflammatory Diseases. J Diabetes Res. PMC6151376
- Hoon MW et al. (2013). The effect of nitrate supplementation on exercise performance. J Acad Nutr Diet. PubMed 22248502
- Nobel Prize 1998. Furchgott, Ignarro, Murad — for discoveries concerning nitric oxide as a signalling molecule in the cardiovascular system.
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