Nitric oxide is one of the most important molecules your body produces. It keeps blood vessels relaxed, helps regulate blood pressure, supports immune defense, and plays a role in exercise performance. Your body makes it naturally, and levels decline with age, which is why so many people search for ways to boost it. The short answer: maintaining healthy nitric oxide levels is genuinely beneficial, and for most people, the best way to do that is through diet.
What Nitric Oxide Does in Your Body
Nitric oxide is a signaling molecule produced inside the lining of your blood vessels. Cells there convert the amino acid L-arginine into nitric oxide using a specialized enzyme. Once produced, nitric oxide drifts into the smooth muscle surrounding your blood vessels and triggers them to relax and widen. This process, called vasodilation, is how your body fine-tunes blood flow to organs, muscles, and your brain moment by moment.
The effect on blood pressure is substantial. When researchers blocked nitric oxide production in healthy volunteers using a drug that shuts down the enzyme responsible, systolic blood pressure jumped from an average of 108 to 127 mmHg, and diastolic pressure rose from 63 to 90 mmHg. That’s a shift from perfectly normal blood pressure into stage-1 hypertension, caused solely by removing nitric oxide from the equation. It demonstrates just how much continuous work this molecule does to keep your cardiovascular system in check.
Immune Defense
Beyond blood vessels, nitric oxide is a weapon your immune system uses against infections. Macrophages, a type of white blood cell that engulfs invaders, produce sustained bursts of nitric oxide that are directly toxic to viruses, bacteria, fungi, and even parasites. This antimicrobial action gets amplified when combined with other compounds macrophages release, including hydrogen peroxide and superoxide. Nitric oxide also has anti-tumor activity, making it part of the body’s surveillance system against abnormal cell growth.
Exercise Performance
Nitric oxide’s ability to open blood vessels means more oxygen-rich blood reaches working muscles during exercise. This is why beetroot juice and nitrate supplements have become popular among athletes. The idea is sound: dietary nitrates convert to nitric oxide in your body and could theoretically improve endurance.
The actual evidence is more nuanced than supplement marketing suggests. A study published in the International Journal of Exercise Science found that a single dose of dietary nitrate had no measurable impact on oxygen consumption during either maximal or submaximal exercise in recreationally active men. The researchers concluded that while nitrate supplementation may offer performance benefits for elite athletes training at very high intensities, everyday exercisers are unlikely to notice a difference. If you’re a competitive endurance athlete pushing your limits, there may be a marginal edge. If you’re jogging three times a week, beetroot juice won’t transform your workouts.
Best Food Sources of Nitric Oxide
Your body produces nitric oxide through two pathways. The first uses L-arginine directly. The second converts dietary nitrates (found in vegetables) into nitrite in your mouth, then into nitric oxide in your bloodstream. Eating nitrate-rich vegetables is the most reliable way to support both pathways.
The highest-nitrate vegetables, measured in milligrams per 100 grams:
- Radish: 625 mg
- Beetroot: 495 mg
- Tarragon: 424 mg
- Lettuce: 365 mg
- Mint: 279 mg
- Celery: 261 mg
For comparison, fruits contain only 7 to 47 mg per 100 grams, meats range from 6 to 19 mg, and dairy products hover between 1 and 6 mg. Vegetables dominate this category so thoroughly that a single serving of beetroot delivers more nitrate than a full day’s worth of meat and dairy combined. Leafy greens like arugula and spinach are also well-known high-nitrate foods, and regularly eating a variety of these vegetables gives your body a steady supply of raw material for nitric oxide production.
Supplements: L-Arginine vs. L-Citrulline
Two amino acid supplements are commonly marketed for boosting nitric oxide: L-arginine and L-citrulline. L-arginine is the direct precursor your body uses to make nitric oxide, so it seems like the obvious choice. But L-citrulline is actually more effective at raising nitric oxide levels.
The reason comes down to how your body processes each one. Much of the L-arginine you swallow gets broken down in the gut and liver before it reaches your bloodstream. L-citrulline bypasses that breakdown, gets absorbed intact, and then converts to L-arginine inside your cells, right where nitric oxide synthesis happens. The three enzymes responsible for recycling citrulline into nitric oxide work together as a complex, efficiently channeling citrulline toward nitric oxide production. The result is that citrulline supplementation raises nitric oxide output more than an equivalent dose of arginine.
How Much Nitrate Is Safe
The joint expert committee of the World Health Organization and the Food and Agriculture Organization sets the acceptable daily intake for nitrate at up to 3.7 mg per kilogram of body weight. For a 70 kg (154 lb) person, that works out to about 259 mg per day. A 100-gram serving of beetroot (495 mg of nitrate) technically exceeds that guideline on its own.
This sounds alarming, but context matters. The ADI was set conservatively and is based largely on concerns about nitrate converting to nitrite, which can interfere with oxygen transport in the blood at very high doses. In practice, healthy adults eating a vegetable-rich diet rarely experience problems. The nitrate in vegetables comes packaged with vitamin C and polyphenols, which steer nitrite toward beneficial nitric oxide production rather than harmful byproducts. The concern is more relevant for infants, who are genuinely vulnerable to nitrite’s effects on blood oxygen, and for people consuming large amounts of processed meats, where nitrate and nitrite behave differently than in plant foods.
Who Should Be Cautious
Because nitric oxide lowers blood pressure by relaxing blood vessels, people who already have low blood pressure or who take blood pressure medications should be careful about aggressively supplementing. Stacking nitric oxide boosters on top of antihypertensive drugs can cause blood pressure to drop too far, leading to dizziness, fainting, or worse.
People with heart failure or significant lung conditions should also approach nitric oxide supplementation with caution, as it can worsen certain cardiovascular dynamics in those populations. And anyone taking medications that interact with nitric oxide pathways, particularly drugs for pulmonary hypertension, should avoid supplementation without medical guidance. For the vast majority of healthy adults, though, getting nitric oxide from a diet rich in leafy greens, beets, and citrus fruits (which support nitric oxide preservation) is both safe and beneficial.