Lab Reference Library / Nitric Oxide Inflammation and Cardiovascular

Nitric Oxide

Q: What is nitric oxide and why is it important?

Nitric oxide (NO) is a gaseous signaling molecule produced by the endothelium (the inner lining of blood vessels). It is the primary vasodilator in the cardiovascular system, relaxing blood vessel walls to increase blood flow and reduce blood pressure. NO also prevents platelet aggregation (reducing clot risk), inhibits smooth muscle proliferation in arterial walls (slowing atherosclerosis), modulates immune function, and supports neurotransmission. The 1998 Nobel Prize in Physiology or Medicine was awarded for the discovery of NO as a cardiovascular signaling molecule.

Q: How is nitric oxide tested?

NO cannot be measured directly because it has a half-life of only a few seconds. It is assessed through serum nitrate and nitrite (NOx), its stable metabolites; salivary nitric oxide test strips, which measure the nitrate-nitrite conversion capacity of oral bacteria (a convenient point-of-care screening tool); and clinical assessment including blood pressure, erectile function, exercise tolerance, and endothelial function testing (flow-mediated dilation). The salivary strip test is the most accessible screening method and correlates with overall NO production capacity.

Q: What depletes nitric oxide?

Aging (eNOS activity declines progressively after age 40), endothelial dysfunction from oxidative stress and inflammation, insulin resistance and hyperglycemia (glucose damages eNOS through uncoupling), mouthwash use (kills the oral bacteria that convert dietary nitrate to nitrite in the enterosalivary pathway), antacid medications (stomach acid is required to convert nitrite to NO), low dietary nitrate intake (insufficient substrate), sedentary lifestyle (exercise is a primary eNOS stimulus through shear stress), and smoking (directly damages endothelial cells and reduces eNOS expression).

Q: How do you increase nitric oxide naturally?

Two pathways produce NO: the eNOS pathway (endothelial enzyme converts L-arginine to NO, stimulated by exercise and shear stress) and the nitrate-nitrite-NO pathway (dietary nitrate from beets, leafy greens, and other vegetables is converted to nitrite by oral bacteria and then to NO in the stomach and tissues). Both pathways should be supported: exercise (the most potent eNOS stimulus), dietary nitrate-rich foods (beet juice, arugula, spinach, celery), L-citrulline supplementation (recycled to L-arginine more efficiently than L-arginine itself), and avoidance of antiseptic mouthwash (which kills the oral bacteria essential for the nitrate-nitrite pathway).

Q: Does mouthwash reduce nitric oxide?

Yes. Antiseptic mouthwash (chlorhexidine, cetylpyridinium chloride, and alcohol-based mouthwashes) kills the facultative anaerobic bacteria on the tongue that convert dietary nitrate to nitrite. This enterosalivary pathway accounts for approximately 25% of total daily NO production and becomes the dominant NO production pathway as eNOS declines with age. Studies show that twice-daily antiseptic mouthwash use raises systolic blood pressure by 2 to 3.5 mmHg within one week by reducing NO availability. Patients with hypertension or cardiovascular risk should avoid antiseptic mouthwash.

NO · Nitric Oxide Metabolites · NOx (Nitrate + Nitrite)

Reference range, optimal functional medicine interpretation, and why nitric oxide is the master vasodilator controlling blood pressure, endothelial function, blood flow, and cardiovascular health. Measured indirectly through serum nitrate/nitrite (NOx) or salivary nitric oxide test strips. Declines with aging, endothelial dysfunction, and insulin resistance.

Cardiovascular MarkerEndothelial Function

Standard RangeNOx varies by lab

FM OptimalFunctional assessment

Fasting RequiredPreferred

AssessmentSerum NOx or saliva

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Category: Inflammation and Cardiovascular | Also known as: NO, Nitric Oxide Metabolites, NOx (Nitrate + Nitrite) | Sample: Serum (NOx) or salivary test strip (fasting preferred)

1. What This Test Measures

Nitric oxide (NO) is a gaseous signaling molecule produced primarily by endothelial cells through the enzyme endothelial nitric oxide synthase (eNOS). The 1998 Nobel Prize in Physiology or Medicine was awarded for the discovery that this simple gas is the primary signaling molecule controlling vascular tone, blood pressure, and cardiovascular function. When eNOS converts the amino acid L-arginine to L-citrulline, NO is released as a byproduct. NO diffuses into the smooth muscle cells surrounding the blood vessel, activates guanylate cyclase, increases cyclic GMP, and produces smooth muscle relaxation (vasodilation). This vasodilation reduces blood pressure, increases blood flow to tissues, and is the mechanism behind erection physiology (PDE-5 inhibitors like sildenafil work by prolonging the NO signal).

NO cannot be measured directly in blood because it has a half-life of only 2 to 6 seconds before being oxidized to nitrite (NO2) and then nitrate (NO3). These stable metabolites, collectively called NOx, serve as indirect markers of NO production. Serum NOx can be measured by standard laboratory assays. More practically, salivary nitric oxide test strips measure the conversion capacity of the enterosalivary nitrate-nitrite-NO pathway, providing a convenient point-of-care assessment of overall NO status.

The body produces NO through two complementary pathways. The eNOS pathway (enzymatic): endothelial cells convert L-arginine to NO using eNOS. This pathway is stimulated by exercise (shear stress on vessel walls), adequate L-arginine and L-citrulline substrate, and cofactors (BH4, NADPH). The nitrate-nitrite-NO pathway (dietary): dietary nitrate from vegetables (beets, arugula, spinach) is concentrated in saliva by the salivary glands, converted to nitrite by facultative anaerobic bacteria on the tongue, swallowed, and converted to NO in the acidic stomach environment and in peripheral tissues. This pathway becomes increasingly important with aging as eNOS activity declines.

2. Why This Test Matters

Blood pressure regulation: NO is the primary vasodilator maintaining normal blood pressure. Endothelial dysfunction with reduced NO production is the earliest identifiable stage of hypertension and cardiovascular disease
Atherosclerosis prevention: NO inhibits three critical steps in atherosclerosis: monocyte adhesion to the endothelium (the first step in plaque formation), smooth muscle cell proliferation in arterial walls, and platelet aggregation. Reduced NO accelerates all three processes
Erectile function: erection requires NO-mediated vasodilation of penile arterial smooth muscle. Erectile dysfunction is often the earliest clinical manifestation of systemic endothelial dysfunction and reduced NO production, preceding cardiovascular events by 3 to 5 years
Exercise capacity: NO-mediated vasodilation determines blood flow to working muscles during exercise. Reduced NO production limits exercise performance, oxygen delivery, and recovery capacity
Aging biomarker: eNOS activity and NO production decline progressively with age. This decline is one of the primary mechanisms driving the age-related increase in blood pressure, cardiovascular risk, and endothelial dysfunction
Insulin sensitivity: NO mediates insulin-stimulated glucose uptake in skeletal muscle by increasing blood flow to muscle capillary beds. Reduced NO impairs glucose disposal and contributes to insulin resistance
Immune modulation: inducible NOS (iNOS) in macrophages produces NO as an antimicrobial defense mechanism. NO balance between eNOS (protective, low-output) and iNOS (inflammatory, high-output) determines whether NO signaling is cardiovascular-protective or tissue-damaging

3. Standard Lab Reference Range

Assessment Method	Reference Range	Clinical Notes
Serum NOx (nitrate + nitrite)	10 to 65 umol/L (varies by lab)	Reflects total NO production; influenced by dietary nitrate intake; fasting preferred
Salivary NO strip test	Colorimetric scale	Point-of-care screening; measures enterosalivary pathway capacity; depleted = low NO
Flow-mediated dilation (FMD)	Above 7% dilation	Gold standard for endothelial function; measures brachial artery NO-dependent vasodilation

4. Optimal Functional Medicine Assessment

Indicator	Functional Interpretation
Salivary strip: robust color	Adequate NO production capacity; enterosalivary pathway intact
Salivary strip: depleted	Reduced NO status; investigate eNOS dysfunction, dietary nitrate deficiency, or mouthwash-mediated bacterial disruption
BP well-controlled without meds	Suggests adequate NO-mediated vasodilation
Resistant hypertension	Consider NO depletion as a contributing mechanism alongside other drivers
Erectile dysfunction present	Likely marker of systemic NO deficiency and endothelial dysfunction

The mouthwash connection: antiseptic mouthwash (chlorhexidine, alcohol-based formulations) kills the oral bacteria that convert dietary nitrate to nitrite. This enterosalivary pathway accounts for approximately 25% of total NO production and becomes the dominant pathway as eNOS declines with age. Studies demonstrate that twice-daily antiseptic mouthwash raises systolic blood pressure by 2 to 3.5 mmHg within one week. Patients with hypertension or cardiovascular risk should avoid antiseptic mouthwash.

5. Nitric Oxide in the Complete Cardiovascular Panel

NO assessment is one component of a comprehensive cardiovascular and endothelial evaluation:

Marker	What It Adds	FM Optimal
Nitric Oxide (this page)	Endothelial vasodilation capacity; blood pressure regulation	Robust salivary strip; NOx upper half
hs-CRP	Vascular inflammation; drives eNOS uncoupling	Below 1.0 mg/L
Oxidized LDL	Atherogenic LDL; NO inhibits LDL oxidation	Below 60 U/L
Lp-PLA2	Vascular-specific inflammation; plaque instability marker	Below 200 ng/mL
Fasting Insulin	Insulin resistance impairs NO-mediated glucose disposal	2 to 6 uIU/mL
Vitamin D	Supports eNOS expression and endothelial function	60 to 80 ng/mL

6. Symptoms Associated With Low Nitric Oxide

Cardiovascular and Vascular

Elevated blood pressure (especially systolic)
Resistant hypertension not responding to single-agent therapy
Cold hands and feet (peripheral vasoconstriction)
Reduced exercise tolerance and early fatigue during exertion
Erectile dysfunction (often the earliest sign of systemic NO deficiency)
Angina or chest tightness with exertion
Poor wound healing and slow recovery from injury

Metabolic and Systemic

Declining exercise performance despite consistent training
Muscle cramps and poor exercise recovery
Cognitive decline (reduced cerebral blood flow)
Headaches (paradoxical: both NO excess and deficiency cause headaches)
Increased platelet aggregation tendency
Accelerated atherosclerosis on imaging
Insulin resistance worsening despite dietary effort

7. What Depletes Nitric Oxide

Aging: eNOS expression and activity decline progressively after age 40. By age 70, endothelial NO production is reduced by approximately 75% compared to age 25. This is one of the primary mechanisms driving age-related hypertension
Oxidative stress and eNOS uncoupling: when the eNOS cofactor tetrahydrobiopterin (BH4) is depleted by oxidative stress, eNOS becomes "uncoupled" and produces superoxide (a damaging free radical) instead of NO. This converts a protective enzyme into a destructive one
Insulin resistance and hyperglycemia: elevated glucose produces advanced glycation end products (AGEs) that damage endothelial cells and reduce eNOS expression. Hyperinsulinemia also impairs NO-mediated vasodilation
Antiseptic mouthwash: kills the tongue bacteria (Veillonella, Actinomyces, Rothia species) that convert dietary nitrate to nitrite. This disrupts approximately 25% of total NO production
Proton pump inhibitors (PPIs): stomach acid is required to convert swallowed nitrite to NO. PPIs reduce gastric acid production and impair this conversion step
Smoking: directly damages endothelial cells, reduces eNOS expression, increases oxidative stress, and depletes BH4. Smoking is one of the most destructive insults to NO production
Sedentary lifestyle: exercise produces shear stress on vessel walls, which is the primary mechanical stimulus for eNOS activation. Physical inactivity removes this stimulus
Chronic inflammation: elevated hs-CRP and inflammatory cytokines damage the endothelium and drive eNOS uncoupling
Low dietary nitrate: insufficient intake of nitrate-rich vegetables (beets, leafy greens) reduces the substrate available for the nitrate-nitrite-NO pathway

8. How to Optimize Nitric Oxide Production

Dietary Nitrate Pathway

Beet juice or beet powder: the richest dietary source of inorganic nitrate. 500mL of beet juice (or equivalent beet powder) provides approximately 6 to 8 mmol nitrate and has demonstrated 4 to 5 mmHg systolic blood pressure reduction in clinical trials
Leafy greens: arugula (the highest nitrate vegetable), spinach, lettuce, kale, chard. Two or more servings daily provides significant dietary nitrate
Other nitrate sources: celery, radishes, turnips, Chinese cabbage, parsley. Cooking reduces nitrate content; raw or lightly cooked is preferred
Stop antiseptic mouthwash: preserve the oral bacteria that convert nitrate to nitrite. Use non-antiseptic oral hygiene (brushing, flossing, water rinse) instead
Maintain stomach acid: avoid unnecessary PPI use; stomach acid converts nitrite to NO. If PPI is medically necessary, increase dietary nitrate to compensate

eNOS Pathway (Exercise and Lifestyle)

Aerobic exercise: the most potent eNOS stimulus. Exercise increases blood flow velocity (shear stress) on the endothelial surface, activating eNOS. 150 to 200 minutes weekly of moderate-intensity aerobic exercise produces sustained eNOS upregulation
Resistance training: produces acute blood flow increases and shear stress; complements aerobic exercise for NO production
Nasal breathing during exercise: nasal breathing adds NO produced in the paranasal sinuses to inspired air, improving bronchodilation and oxygen delivery. Mouth breathing bypasses this sinus-derived NO
Sunlight exposure: UVA radiation releases NO from skin nitrate stores, producing measurable blood pressure reduction independent of vitamin D
Smoking cessation: the single most impactful modifiable factor for endothelial NO recovery

Targeted Supplementation

L-citrulline (3 to 6g daily): recycled to L-arginine in the kidneys more efficiently than L-arginine supplementation itself. Raises plasma arginine levels more reliably, providing sustained eNOS substrate. Preferred over L-arginine for NO support
Beetroot extract (500 to 1000mg daily): concentrated dietary nitrate in supplement form for patients who do not consume adequate nitrate-rich vegetables
Vitamin C (500 to 1000mg daily): protects BH4 (the eNOS cofactor) from oxidative degradation, preventing eNOS uncoupling. One of the most important cofactors for maintaining eNOS function
Folate (L-5-MTHF, 800mcg daily): supports BH4 recycling and eNOS coupling. Folate deficiency contributes to eNOS uncoupling and superoxide production
Omega-3 fatty acids (2 to 3g EPA/DHA daily): anti-inflammatory; reduces the endothelial inflammation that drives eNOS dysfunction

9. Related Lab Tests

hs-CRPVascular Inflammation Driving eNOS Uncoupling

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Oxidized LDLNO Inhibits LDL Oxidation; Atherogenic Marker

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Lp-PLA2Vascular-Specific Inflammation Marker

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Fasting InsulinInsulin Resistance Impairs NO Vasodilation

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Vitamin DSupports eNOS Expression

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Hemoglobin A1cGlycation Damages Endothelial eNOS

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10. When Testing Is Recommended

Patients with hypertension, especially resistant hypertension not responding to standard first-line therapy
Erectile dysfunction: NO deficiency is the most common mechanism; evaluate before or alongside PDE-5 inhibitor prescription
Comprehensive cardiovascular risk assessment alongside hs-CRP, oxidized LDL, and Lp-PLA2
Endothelial dysfunction evaluation: NO is the primary functional output of healthy endothelium
Patients on antiseptic mouthwash with rising blood pressure: salivary NO strip confirms mouthwash-mediated NO depletion
Declining exercise performance, cold extremities, or poor exercise recovery suggesting vascular insufficiency
Patients with insulin resistance: NO-mediated glucose disposal impairment contributes to metabolic dysfunction
Longevity assessment: NO production capacity as a biomarker of vascular aging

11. Clinical Perspective

Clinical Perspective

I ask every patient with hypertension whether they use mouthwash. Most do, and most have never been told that their twice-daily Listerine is raising their blood pressure by killing the bacteria that make nitric oxide. It sounds too simple to be important, but the data is clear: antiseptic mouthwash measurably raises blood pressure within days by disrupting the enterosalivary nitrate-nitrite-NO pathway. This pathway becomes the dominant source of NO as we age and eNOS declines. Beyond mouthwash, I find that most patients with hypertension or erectile dysfunction have never been evaluated for NO status. They receive a prescription for an ACE inhibitor or a PDE-5 inhibitor without anyone asking whether the underlying problem is NO deficiency. Beet juice, L-citrulline, exercise, and stopping mouthwash are interventions that address the mechanism. They are not alternatives to medication in every case, but they are foundational, and in many patients, they produce blood pressure reductions that rival first-line drugs.

Brian Lamkin, DO | Founder, The Lamkin Clinic | Edmond, Oklahoma

12. Frequently Asked Questions

What is nitric oxide and why is it important?

A gaseous signaling molecule produced by the endothelium. The primary vasodilator: relaxes blood vessel walls to increase flow and reduce blood pressure. Also prevents platelet aggregation, inhibits atherosclerosis, supports immune function, and mediates erectile function. Nobel Prize awarded in 1998 for its discovery as a cardiovascular signal.

How is nitric oxide tested?

Indirectly: serum nitrate/nitrite (NOx) measures stable metabolites; salivary NO test strips measure enterosalivary pathway capacity (convenient point-of-care screening); flow-mediated dilation (FMD) is the gold standard for endothelial function. The salivary strip is the most accessible method and correlates with overall NO status.

What depletes nitric oxide?

Aging (eNOS activity declines after 40), oxidative stress (eNOS uncoupling), insulin resistance, antiseptic mouthwash (kills nitrate-converting bacteria), PPIs (reduce stomach acid needed for nitrite-to-NO conversion), smoking, sedentary lifestyle, and low dietary nitrate intake. Multiple depletors typically coexist.

How do you increase nitric oxide naturally?

Two pathways: eNOS (stimulated by aerobic exercise through shear stress) and dietary nitrate-nitrite-NO (beet juice, arugula, spinach converted by oral bacteria). L-citrulline (3 to 6g daily) provides sustained eNOS substrate. Stop antiseptic mouthwash. Vitamin C protects the BH4 cofactor. Nasal breathing during exercise adds sinus-derived NO.

Does mouthwash reduce nitric oxide?

Yes. Antiseptic mouthwash kills the tongue bacteria converting dietary nitrate to nitrite (approximately 25% of total NO production). Studies show twice-daily use raises systolic blood pressure 2 to 3.5 mmHg within one week. This pathway becomes dominant as eNOS declines with age. Patients with hypertension or cardiovascular risk should avoid antiseptic mouthwash.

Content authored and clinically reviewed by Brian Lamkin, DO, founder of The Lamkin Clinic in Edmond, Oklahoma. Brian Lamkin, DO has 25+ years of experience in functional and regenerative medicine. This page reflects current functional medicine practice standards and is updated as new clinical evidence becomes available.

Nitric oxide is the molecule that determines whether your blood vessels relax or constrict, whether blood flows or clots, and whether your endothelium protects or promotes disease.

Comprehensive cardiovascular assessment includes NO status alongside hs-CRP, oxidized LDL, Lp-PLA2, and metabolic markers. Identify the mechanism driving your blood pressure and endothelial function. Schedule a consultation at The Lamkin Clinic.

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Medical Disclaimer: This content is provided for educational purposes only and is not intended as a substitute for professional medical advice, diagnosis, or treatment. Lab interpretation should always be performed in clinical context by a qualified healthcare provider. Reference ranges and optimal targets may vary based on individual patient history, clinical presentation, and laboratory methodology. Schedule a consultation to discuss your specific results with Brian Lamkin, DO.