What Depletes Nitric Oxide in the Body?

Nitric oxide is depleted by a surprisingly wide range of everyday factors, from the foods you eat to how much you move, the medications in your cabinet, and even the mouthwash you use before bed. The core mechanism is often the same: something generates excess free radicals that intercept nitric oxide before it can do its job, or something cripples the enzyme responsible for making it in the first place. But the list of triggers is long, and some of them are things most people would never suspect.

The Central Problem With Free Radicals

Your body produces nitric oxide continuously, but it also produces reactive oxygen species as a normal byproduct of metabolism. When those two are in balance, everything works. The trouble starts when free radical production tips the scale. Superoxide, a particularly important free radical, reacts with nitric oxide almost instantly in a reaction so fast it is essentially limited only by how quickly the two molecules bump into each other. The product of that collision is peroxynitrite, a potent oxidant that not only removes nitric oxide from circulation but can go on to damage proteins and DNA.¹ Most of the tissue damage once blamed on nitric oxide itself is now thought to be caused by peroxynitrite instead.²

This matters because nearly every item on the “what depletes nitric oxide” list ultimately works through this pathway, boosts it, or feeds into it. Anything that increases superoxide production, whether it is cigarette smoke, air pollution, a high-salt diet, or prolonged sitting, drains your nitric oxide supply by the same basic chemistry. Understanding this single reaction explains why so many seemingly unrelated habits converge on the same cardiovascular problems.

How the Enzyme That Makes Nitric Oxide Turns Against You

The enzyme responsible for most of your vascular nitric oxide is called endothelial nitric oxide synthase, or eNOS. Under healthy conditions, eNOS converts the amino acid L-arginine into nitric oxide. But eNOS needs a helper molecule called tetrahydrobiopterin (BH4) to work properly. When BH4 gets oxidized or destroyed, eNOS “uncouples,” meaning it stops producing nitric oxide and starts producing superoxide instead.³ This creates a vicious cycle: the superoxide that uncoupled eNOS generates reacts with remaining nitric oxide to form peroxynitrite, and peroxynitrite itself oxidizes more BH4, which uncouples more eNOS.⁴

This feed-forward loop is a recurring theme across many of the specific causes discussed below. Whether the initial trigger is smoking, sleep apnea, or chronic inflammation, the downstream story often involves BH4 depletion and eNOS uncoupling.

Smoking and Air Pollution

Cigarette smoke attacks nitric oxide production from multiple angles. Smoke constituents deplete BH4 and also reduce the expression of the enzyme that makes BH4 in the first place, essentially cutting off both the existing supply and the body’s ability to replenish it.⁵ In animal studies, chronic smoke exposure progressively depleted BH4 over time, leading to uncoupled eNOS, rising superoxide levels, and worsening blood vessel function.⁶ Acrolein, one of the most toxic chemicals in cigarette smoke, directly reduces eNOS activity and lowers its total protein levels in endothelial cells.⁷

You do not need to be a smoker to be affected. Diesel exhaust particles generate free radicals that directly scavenge nitric oxide in blood vessels. In lab experiments, diesel particles increased free radical generation roughly ninefold and significantly reduced the ability of arteries to relax in response to nitric oxide signals.⁸ Urban particulate matter has been shown to impair nitric oxide activity in lung arteries specifically.⁹ For people living near highways or in cities with poor air quality, this is a chronic, low-grade drain on nitric oxide that compounds over years.

Sitting Too Much

Your endothelial cells sense blood flow. When blood moves quickly through an artery, the friction against the vessel wall, known as shear stress, signals eNOS to ramp up nitric oxide production. Prolonged sitting slashes blood flow through your legs, pools blood in your calves, and drops shear stress to levels where nitric oxide production falls off.¹⁰ The resulting low-nitric-oxide environment shifts the vessel lining toward a pro-oxidant state, which means even more nitric oxide gets scavenged by free radicals. If your job involves sitting for hours at a stretch, this is one of the most immediate and modifiable factors on the list.

Dietary Hits From Fat and Salt

A single high-fat meal can measurably reduce your circulating nitric oxide metabolites within hours. In one study, young, normal-weight individuals who were more sensitive to postprandial fat showed a drop of about 17% in plasma nitric oxide metabolites after eating a high-fat meal, compared to roughly 5% in those who were less reactive.¹¹ The people who reacted most strongly tended to show signs of insulin resistance, suggesting that metabolic health amplifies or buffers this effect.

High sodium intake is another dietary drain. Research in both animals and humans shows that excess dietary salt reduces nitric oxide availability in blood vessels even when blood pressure does not rise.¹² The mechanism appears to involve the sodium itself stiffening endothelial cells and directly dampening nitric oxide release.¹³ This is a distinction worth noting: the vascular harm from salt is not entirely mediated through blood pressure. Even if your pressure stays normal on a high-salt diet, your nitric oxide system may still be taking a hit.¹⁴

Mouthwash and the Bacteria You Actually Need

This one surprises most people. Your body has a backup system for producing nitric oxide that does not involve eNOS at all. When you eat nitrate-rich foods like leafy greens and beets, that nitrate circulates in your blood, gets concentrated in your saliva by your salivary glands, and is then converted to nitrite by bacteria living on the back of your tongue. That nitrite gets swallowed and eventually converted to nitric oxide in your stomach and bloodstream. Antiseptic mouthwashes, particularly those containing chlorhexidine, wipe out these nitrate-reducing bacteria and effectively shut down this entire pathway.¹⁵

The effect is not subtle. In one trial, seven days of chlorhexidine mouthwash use cut oral nitrite production by about 90% and lowered plasma nitrite levels by roughly 25%. Blood pressure rose by 2 to 3.5 mmHg, and that increase appeared within a single day of starting the mouthwash.¹⁶ Other research confirmed that chlorhexidine reduced oral nitrate-reducing capacity and lowered both saliva and plasma nitrite levels.¹⁷ This does not mean you should never use mouthwash, but if you are using a strong antiseptic formula daily while also trying to lower your blood pressure through a nitrate-rich diet, the mouthwash may be canceling out your dietary efforts.

Medications That Interfere

Proton pump inhibitors, the class of drugs used for acid reflux and ulcers, suppress stomach acid. That acid turns out to be important for converting swallowed nitrite into nitric oxide. Research shows that PPIs decrease gastric nitric oxide formation from nitrite and are associated with increased cardiovascular risk.¹⁸ In controlled experiments, the blood-pressure-lowering effect of ingested nitrite was completely abolished when stomach acid was suppressed by a PPI.¹⁹ If you take a PPI daily and also eat plenty of beets and greens for their nitrate content, the stomach step of the conversion chain may be broken.

Nonsteroidal anti-inflammatory drugs, both selective and non-selective types, also reduce vascular nitric oxide production. These drugs increased oxidative stress in blood vessels and reduced circulating nitrite, a marker of nitric oxide availability.²⁰ This finding aligns with the long-observed link between chronic NSAID use and elevated cardiovascular risk, especially in older adults.

There is also an endogenous molecule worth knowing about. Your body naturally produces a compound called ADMA (asymmetric dimethylarginine), which competes with L-arginine at the active site of eNOS and inhibits nitric oxide production. ADMA levels rise in conditions associated with cardiovascular disease, and elevated ADMA is now considered an independent cardiovascular risk factor.²¹ Separately, overexpression of the enzyme arginase can deplete L-arginine, the raw material eNOS needs, effectively starving the enzyme. This has been documented in preeclampsia, where elevated arginase activity in the placenta diverts arginine away from nitric oxide production.²²

Chronic Stress and Cortisol

Psychological stress does not stay psychological for long. Chronic stress raises cortisol, and cortisol directly suppresses nitric oxide. In endothelial cell experiments, cortisol caused a dose-dependent drop in nitric oxide release by reducing eNOS protein levels and speeding up eNOS degradation. It also blunted the calcium signaling that eNOS depends on to activate.²³ In animals subjected to chronic crowding stress, nitric oxide production dropped persistently in the brain and heart, and these reductions lasted at least two weeks after the stress was removed. The animals predisposed to high blood pressure were hit the hardest.²⁴

Chronic Inflammation and Metabolic Disease

When your body mounts a sustained inflammatory response, certain signaling molecules actively dismantle nitric oxide production. TNF-alpha, one of the most studied inflammatory cytokines, decreases eNOS expression in endothelial cells.²⁵ It does this in part by increasing a micro-RNA called miR-155, which directly targets and silences eNOS. When researchers blocked miR-155, the TNF-alpha-induced damage to eNOS expression and vessel relaxation was reversed.²⁶ Conditions that keep TNF-alpha chronically elevated, such as obesity, rheumatoid arthritis, and inflammatory bowel disease, therefore impose a continuous drag on nitric oxide availability.

Type 2 diabetes illustrates how metabolic disease compounds the problem. In people with type 2 diabetes and kidney involvement, the actual rate of nitric oxide synthesis was markedly lower than in healthy controls, both at rest and when stimulated by insulin. Insulin normally boosts nitric oxide production, but in the diabetic participants this stimulatory effect was several-fold weaker.²⁷ This helps explain why cardiovascular complications are so common in diabetes: the metabolic environment suppresses one of the body’s main vascular protective systems.

Sleep Apnea and Intermittent Oxygen Drops

Obstructive sleep apnea causes repeated episodes of low oxygen throughout the night. These oxygen dips trigger the same cascade seen elsewhere: oxidative stress, BH4 depletion, and eNOS uncoupling. In cell experiments mimicking the intermittent hypoxia of sleep apnea, eNOS activity dropped by about 65%, nitric oxide metabolites fell by roughly 55%, and the BH4-to-BH2 ratio plummeted by 70%.²⁸ Animal studies of chronic intermittent hypoxia tell a complementary story: in carotid arteries, levels of arginase (the enzyme that competes with eNOS for arginine) went up while eNOS levels went down, tipping the balance away from nitric oxide production.²⁹ For the millions of people with untreated sleep apnea, this nightly assault on the nitric oxide system is a plausible mechanism behind the well-known link between sleep apnea and hypertension.

Aging and Hormone Shifts

Nitric oxide availability naturally declines with age. This is driven by multiple converging forces: eNOS activity decreases, oxidative stress rises, and metabolic changes accumulate that all push nitric oxide levels downward.³⁰ In women, the menopause transition introduces an additional factor. Estradiol supports endothelial function, and as estrogen levels fall during perimenopause and menopause, blood vessel function measurably declines. Research using a drug to temporarily suppress ovarian hormones in premenopausal women showed that removing estrogen alone was enough to impair vessel dilation, and adding estradiol back restored it. In late perimenopausal and postmenopausal women, vitamin C (an antioxidant) improved vessel function, suggesting that oxidative stress is a key driver of the problem at that stage.³¹

Your body’s internal clock also plays a role. The enzymes that produce and recycle BH4 follow a circadian rhythm. In mice lacking a functional circadian clock gene, BH4 levels in arteries were reduced and BH2 (the inactive, oxidized form) was elevated, leading to eNOS uncoupling and excess superoxide. Supplementing BH4 improved their endothelial function.³² The practical implication: chronic disruption of circadian rhythms through shift work, irregular sleep, or constant jet lag may impair BH4 recycling and thereby reduce nitric oxide availability, though direct human data on this specific pathway remains limited.

Sunlight and a Counterintuitive Source of Nitric Oxide

Your skin stores nitric oxide precursors that can be released by ultraviolet light, particularly UVA wavelengths. Lab experiments on skin cells show that even low doses of daylight-equivalent UV exposure trigger nitric oxide release without causing significant DNA damage.³³ This suggests that people who spend almost all their time indoors or who live at high latitudes with limited sunlight may miss out on a meaningful source of nitric oxide. The researchers noted that this mechanism could be particularly relevant for elderly populations, who already face declining nitric oxide from other causes. Sunscreen blocks UVB far more effectively than UVA, so moderate outdoor time may still provide some of this benefit even with sun protection, though the research on this point is still early-stage.