What Is Nitric Oxide?
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Medically reviewed by Kristie Reed, PharmD
Nitric oxide (NO) is a gas formed by combining nitrogen and oxygen. It occurs naturally both outside and inside the body. Outside the body, nitric oxide is a colorless, sweet-smelling gas that is toxic at high levels. Inside the body, it acts as an important chemical messenger involved in many bodily functions. Nitric oxide can also become toxic inside the body when levels get too high.
Research has shown nitric oxide plays a role in neurotransmission, or information sharing between neurons, which helps functions in the nervous system like digestion and memory. It may also encourage the release of hormones, including growth hormones and insulin.
Nitric oxide also acts as a vasodilator, meaning it helps open blood vessels to improve blood flow. It may also improve immunity by promoting inflammation to fight infections.
There are no supplements that contain nitric oxide directly. However, your body uses certain amino acids—L-arginine and L-citrulline—to produce nitric oxide, and these amino acids are available in supplement form. Taking these supplements can raise the amount of nitric oxide in your body.
Another way to get the benefits of increased nitric oxide levels is to eat foods that contain nitrates, which are compounds made of nitrogen and oxygen. Nitrates are found primarily in water and leafy vegetables.
Benefits of Nitric Oxide
Nitric oxide has many potential benefits, but some of the research is limited. Some studies have examined the use of nitric oxide supplementation for insulin release in people with diabetes, or for metabolism management for people with obesity. However, many of these studies are based on animals or very small human groups. While more research is needed to prove these effects, there is more concrete evidence on nitric oxide and its precursor L-arginine’s benefits relating to blood flow.
Improves Vasodilation
Research shows nitric oxide supplementation may promote vasodilation, or the opening of blood vessels.
Vasodilators like nitric oxide help relax the smooth muscle cells in the walls of your blood vessels. This helps promote blood flow through the body. For this reason, increased levels of nitric oxide may help improve conditions related to blood flow and cardiovascular health.
May Help Reduce Hypertension
Nitric oxide helps widen blood vessels to let more blood flow through them. Due to this benefit, it may help reduce blood pressure in people with hypertension, or high blood pressure.
Research has shown L-arginine given intravenously (IV) can be especially beneficial for pregnant women who either have or are at risk for developing pre-eclampsia. Pre-eclampsia involves dangerously high blood pressure during pregnancy. It can be life-threatening to the pregnant parent and to the fetus.
May Help Treat Peripheral Artery Disease
Peripheral artery disease reduces blood flow to the arms and legs. Blood flow is reduced because the arteries have narrowed. A vasodilator like nitric oxide can help widen the arteries and allow more blood to travel into the extremities.
May Reduce Angina
Angina is chest pain that results from reduced blood flow to the heart, and is typically a symptom of heart disease. Nitroglycerin is a type of medication that forms nitric oxide in the body. It relieves angina by relaxing the walls of the blood vessels leading to the heart.
May Help Treat Erectile Dysfunction
Erectile dysfunction (ED) is the inability to get or sustain an erection long enough to have sex. A person’s ability to have an erection depends largely on sufficient blood flow to the penis.
Nitric oxide may help improve blood flow to the penis and therefore reduce symptoms of ED. Taking an L-arginine supplement may be even more effective for ED when taken with medications such as sildenafil and tadalafil.
How to Take Nitric Oxide Supplements
The most common supplement people take to help their body produce nitric oxide is L-arginine. This amino acid is present in foods such as meat and dairy. It also can be taken by mouth as a pill, applied to the skin as a cream, given intravenously (through an IV), or inhaled as a supplement.
However, research shows eating foods rich in nitrates may be safer and more effective than taking L-arginine supplements. Nitrates occur naturally in fruits, vegetables, and water. Green, leafy vegetables like arugula tend to contain the highest concentration of nitrates. Beets, celery, and carrots are also good sources of nitrates.
Eating nitrate-rich foods offers the same potential health benefits as taking supplements that produce nitric oxide. In several studies, for example, drinking beetroot juice seemed to improve oxygen uptake and blood flow during exercise.
Dosage
There is no standard dosage for L-arginine supplements or nitrate-rich foods. The appropriate dose for you will depend on the benefits you desire and your doctor’s recommendation. Keep in mind that most people already get about 5 grams (g) of L-arginine per day from their diet.
That said, taking between 2.5 and 5 g of L-arginine per day seems to be effective in improving ED symptoms in mild to moderate cases. Taking about 6 g per day has been shown to improve strength and power during exercise. Some people take up to 24 g per day to get benefits. However, taking more than 9 g per day may increase the risk of side effects.
Is Nitric Oxide Safe?
Nitric oxide is a type of compound called a free radical. Free radicals are produced naturally during normal cell reactions. They are highly reactive in the body, and they are important for several bodily processes.
However, free radicals are unstable, and at high levels they can build up and create a state called oxidative stress. During oxidative stress, there are not enough antioxidants to control the free radicals. This imbalance can lead to cell damage and ultimately to diseases like cancer.
Taking L-arginine at a controlled level for a short time has been proven to be safe for most people, including pregnant people and children. If you are breastfeeding, have recently had a heart attack, or have liver or kidney disease, L-arginine supplements may not be safe for you. Talk to your healthcare provider before taking this supplement.
Also, people with a genetic condition called guanidinoacetate methyltransferase deficiency (GAMT) may not be able to process arginine. They should not take L-arginine supplements.
Potential Drug Interactions
L-arginine supplements can interact with several medications and other supplements. Ask your healthcare provider about taking it with:
Blood pressure medications. L-arginine may lower your blood pressure. Taking it with other drugs or supplements that also lower your blood pressure may reduce your blood pressure too much.
Diabetes medications. L-arginine may lower your blood sugar. Taking it with drugs or supplements that affect your blood sugar can be dangerous.
Blood thinners. L-arginine may reduce your body’s ability to form blood clots. Bruising and bleeding may occur when you take it with drugs that also slow blood clotting.
Diuretics (water pills). These drugs often contain potassium, and L-arginine may increase potassium levels. Taking them together may lead to potassium levels that are too high.
What to Look For
Dietary supplements are not regulated by the U.S. Food and Drug Administration (FDA) the way medicines are regulated. For this reason, supplements may contain unknown added ingredients, and they may contain less of the active ingredient than they advertise.
Make sure to look for a seal by a third-party quality testing organization on the bottle. These organizations test to make sure the product has the correct type and amount of ingredients listed and does not contain a harmful level of contaminants. Credible third-party testing organizations include:
ConsumerLab.com
NSF International
U.S. Pharmacopeia
In the case of nitric oxide supplementation, adding nitrate-rich foods to your diet may give you the benefits you want without the risks that come with taking dietary supplements.
Can You Take Too Much?
Because nitric oxide is a highly reactive compound, it works quickly to affect many systems in the body. This can lead to several benefits when nitric oxide is balanced out by antioxidants. However, you can take too much L-arginine which could lead to unhealthy levels of nitric oxide in your body. Once you have reached the oxidative stress state, your risk for developing diseases and other health problems increases.
Side Effects of Nitric Oxide
Taking L-arginine supplements to increase nitric oxide levels can lead to side effects. Side effects of L-arginine may include:
Headache
Heartburn
Bloating
Stomach pain
Diarrhea
Vomiting
Low blood pressure
Certain nitric oxide supplements also may trigger herpes outbreaks. Research has also shown a link between high levels of nitric oxide and skin diseases like psoriasis, eczema, and skin cancer. Taking smaller doses or dividing up the doses of nitric oxide supplements may reduce the risk of side effects.
A Quick Review
Nitric oxide is an important chemical messenger in the body. It can promote blood flow, help nerve cells communicate, and may improve immunity. Taking L-arginine supplements or eating a nitrate-rich diet may be beneficial for people with a variety of health problems, including high blood pressure, peripheral artery disease, and erectile dysfunction.
However, nitric oxide is a free radical that can lead to cell and tissue damage when taken in excess. Research about the exact benefits of nitric oxide supplementation with L-arginine is mixed and incomplete. Finally, in addition to causing side effects, L-arginine supplements can be dangerous for certain populations. Talk to your doctor about the possible benefits and risks of nitric oxide for your body.
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