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Nitric Oxide in the Body: Functions, Effects, and Dangers

Linda Crampton is an experienced teacher with a first-class honors degree in biology. She writes about the scientific basis of disease.

Beets are a good source of nitrates, which the body turns into nitrites and then into nitric oxide.

Beets are a good source of nitrates, which the body turns into nitrites and then into nitric oxide.

A Simple and Important Molecule

Nitric oxide is a simple molecule with big effects inside our body. Many biological molecules have a complex structure, but nitric oxide contains just two atoms—a nitrogen atom and an oxygen atom—and has the formula NO. It's sometimes called nitrogen monoxide.

NO has many important biological functions. It relaxes the walls of blood vessels, which causes vasodilation (widening of the vessels). This allows more blood to flow into the heart and other organs. It also acts as a signaling molecule between nerve cells. In addition, it plays an important role in our immune system and helps it to fight infections.

Research suggests that nitric oxide may have an effect on aging and longevity. The possession of intestinal bacteria that make NO enables Caenorhabditis elegans to live for significantly longer than members of its species without the bacteria. C. elegans (the abbreviated scientific name) is a roundworm and a popular organism in anti-aging studies. What applies to a roundworm may not apply to us, but it is known that the level of nitric oxide in our body decreases as we age. The idea that bacteria producing the substance could be added to our intestine in order to help us live longer is a tantalizing thought.

Green vegetables such as romanesco broccoli contain nitrates.

Green vegetables such as romanesco broccoli contain nitrates.

Role of NO in the Circulatory System

Nitric oxide in blood plays a vital role in keeping our circulatory system healthy. It causes vessels to widen and open up, allowing large quantities of blood to be transported through them. Blood without NO doesn't cause vessels to expand. This means that the blood can't flow as easily through the vessels.

Researchers have noticed that the longer that blood is stored before a blood transfusion, the more dangerous it is for the recipient. This seems to be due to the biochemical changes that take place as the blood ages, including loss of nitric oxide gas. Without NO, the donated blood may block the circulatory system because it can't move through the vessels properly. One scientist has shown that in lab animals adding nitric oxide to blood before a transfusion prevents blockage and allows the blood to flow freely.

Nitric oxide also lowers blood pressure. We have some control over this action via the food that we eat. A diet high in leafy green vegetables and beets (also called beetroot) is known to lower high blood pressure. These vegetables are a good source of nitrates. Inside the body, the nitrates are converted to nitrites. The nitrites are converted to nitric oxide. This chemical then expands blood vessels, which lowers blood pressure.

The body also makes NO from an amino acid called L-arginine, which we produce in our body. It's present at a good level in many foods that are a rich source of protein, include some meats, fish, dairy, certain legumes (or pulses), and some nuts and seeds. Proteins are made of amino acids.

Nitroglycerin, Nitric Oxide, and Angina

In 1977, Ferid Murad discovered that nitroglycerin causes the production of nitric oxide in the body. Nitroglycerin (or nitroglycerine) is one medicine given to people suffering from angina. During an angina attack, a person experiences chest pain due to a lack of oxygen in the heart, usually due to the narrowing of a coronary artery. Nitroglycerin can expand this artery. The nitric oxide made from the nitroglycerin is responsible for the vasodilation.

As is true for all medications, a doctor's advice should be followed with respect to the use of nitroglycerin. The timing and frequency of the drug's ingestion are important topics to consider. Other important topics are potential side effects and interactions with other medicines. The formulation of the drug is also important to discuss with a physician. The medication comes in additional forms besides a swallowed version.

A synapse is the region where one neuron ends and another begins.

A synapse is the region where one neuron ends and another begins.

Neurotransmission Facts

Nerve cells, or neurons, communicate with each other by means of chemicals. These chemicals are known as neurotransmitters. A neurotransmitter is produced in advance and stored in small sacs called synaptic vesicles, which are located at the end of a neuron.

The region where one neuron ends and another begins is called a synapse. When a nerve impulse arrives at a synapse, the neurotransmitter is released from the first neuron into the tiny gap that is present between neurons. It then travels through the gap and attaches to receptors on the membrane of the second neuron. Once this union takes place, the second neuron is stimulated (or in some cases inhibited). Stimulation generates a nerve impulse. After it has done its job, the neurotransmitter is broken down or reabsorbed into a nerve cell.

Nitric oxide is a neurotransmitter, but it behaves differently from most of the other chemicals in the category. It isn't produced in advance or stored but is made when it's needed. It does travel across the gap between neurons, but it travels into the second neuron instead of attaching to receptors and staying at the neuron's surface. It may also enter more than one neuron.

Nitric oxide isn't very stable and only exists for a short time. It's sometimes called a "gasotransmitter"—a gas that is made in the body and acts as a signaling molecule.

Radishes contain nitrates that the body uses to produce nitric oxide.

Radishes contain nitrates that the body uses to produce nitric oxide.

Functions in the Nervous System

Nitric oxide has many functions in the central nervous system (the brain and the spinal cord). It plays a role in:

  • learning and memory
  • controlling body temperature
  • regulating food intake
  • controlling the sleep-wake cycle
  • regulating hormone release
  • protecting nerves

The peripheral nervous system is made of nerves that leave the central nervous system and travel to the rest of the body. In the peripheral nervous system nitric oxide does the following:

  • relaxes the muscles in the lining of the gastrointestinal tract
  • relaxes the muscles in the lining of the urinary and reproductive tracts

Neuroprotection and Neurotoxicity of NO

Although nitric oxide is very important in the nervous system, it's present in tiny quantities in our body. These quantities are neuroprotective— they protect the nerves from damage. Large amounts of nitric oxide kill nerve cells and are said to be neurotoxic. This might explain why the results of some research studies involving the chemical disagree with the results of other studies. For example, some research suggests that NO administered to a patient after a stroke helps the patient, while other research suggests that excess NO produced during strokes damages brain cells.

A macrophage extending its pseudopods, which it uses to engulf pathogens

A macrophage extending its pseudopods, which it uses to engulf pathogens

Role of Nitric Oxide in the Immune System

Nitric oxide is made by macrophages, which are a type of white blood cell in our immune system. The NO kills bacteria and inhibits the replication of viruses.

Macrophages and nitric oxide action are part of our innate immune response. This is a rapid, general, and non-specific response that is the same for any pathogen (organism that causes disease). Our other type of immunity is the acquired immune response, which involves an attack that is specific for each pathogen.

Aging and Longevity

Caenorhabditis elegans is a transparent roundworm that lives in soil. Like humans, the roundworm has bacteria that live in its intestine and produce substances that provide health benefits.

C. elegans feeds on a bacterium called Bacillus subtilis. Some of the bacterial cells survive and live in the animal's intestine, where they produce nitric oxide. The worms also eat Escherichia coli, another bacterium that lives in their intestine. Escherichia coli can't make nitric oxide, however.

Worms fed Bacilus subtilis live for about 50 percent longer than worms fed Escherichia coli. This is believed to be at least partly due to the presence or absence of nitric oxide.

One research experiment discovered that C. elegans worms fed normal B. subtilis lived for 15 percent longer than those fed a mutant form of the bacterium that lacked the gene for nitric oxide production. The experiment also confirmed a previous discovery that C. elegans can't produce NO by itself.

C. elegans with a stain added to show its internal anatomy

C. elegans with a stain added to show its internal anatomy

Potential Use of Nitric Oxide in the Future

In the future, nitric oxide may be very useful as a medicine. A major problem will be ensuring that the concentration of the chemical is high enough to be helpful but low enough to be safe. Healthy foods that cause nitric oxide production in the body may be beneficial when eaten in normal quantities. It's not a good idea to eat an excessive amount of any food, even when it's considered to be healthy.

The use of supplements containing nitrogen-containing compounds that the manufacturer claims will stimulate nitric oxide production in the body should be discussed with a doctor. It’s very important that a person doesn’t take a dangerous level of any supplement. Supplementation providing a substance that a person lacks may be useful for some people with a health problem, but the solution and dose must be recommended by a physician.

Researchers need to learn more about nitric oxide’s effects in the body before it's widely used medicinally. It's a simple molecule that is involved in some complex reactions. If NO is administered to treat one health problem, it's important that it doesn't cause another one. Hopefully, researchers will soon make some further discoveries about the substance that will be very helpful for us.


  • Role of Nitric Oxide in Biology from the University of Reading
  • Nobel Prize in Medicine for Nitric Oxide Discovery from Circulation (an American Heart Association journal)
  • Beetroots and blood pressure from Medical News Today
  • Nitroglycerin and NO from the New England Journal of Medicine
  • Information about nitroglyerin medications from the Mayo Clinic
  • Bacteria producing NO extend life in roundworms from the EurekAlert news service
  • The dual effects of nitric oxide in cancer from Science Direct
  • Material Safety Data Sheet (MSDS) for nitric oxide from UCAR (University Corporation for Atmospheric Research)

This content is accurate and true to the best of the author’s knowledge and does not substitute for diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed health professional. Drugs, supplements, and natural remedies may have dangerous side effects. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.

Questions & Answers

Question: How much L-arginine should be ingested each day?

Answer: L-arginine is an amino acid that is present in our diet. It’s found in meat, fish, dairy products, and beans. Most people obtain enough L-arginine as long as they eat a nutritious diet, so they don’t need to be concerned about the intake of the nutrient. A health care professional or a dietitian can recommend dietary methods to increase arginine intake if a person suspects that they aren’t eating enough.

L-arginine is converted to nitric oxide in the body, but it’s unclear whether ingesting the substance as a supplement will boost the nitric oxide level in everyone. Most people don’t need to take supplemental arginine, but people with certain medical problems might benefit from the substance. It’s important that a person consults a doctor before taking an arginine supplement, however. In a supplemental form, the substance can cause major side effects and interact harmfully with certain medications.

If a doctor thinks that supplement arginine will be useful for a patient’s specific medical problem and that the possible side effects of the supplement won’t be harmful to that patient, they’ll recommend a safe and potentially beneficial dose.

© 2013 Linda Crampton


Linda Crampton (author) from British Columbia, Canada on March 03, 2013:

Thanks for the comment, Dianna. It is good to know that broccoli is so healthy!

Dianna Mendez on March 03, 2013:

I love broccoli and am so glad to hear of this additional health benefit. Thanks for the information on how nitric oxide can be good for a body.

Linda Crampton (author) from British Columbia, Canada on February 24, 2013:

Thank you very much, JCielo. I appreciate your comment, as well as the votes and the share!

JCielo from England on February 24, 2013:

Well researched and very well presented. And I love broccolli! Voted up, useful and shared.

Linda Crampton (author) from British Columbia, Canada on February 23, 2013:

Thank you very much for the comment, the votes and the share, Mary! I appreciate them all. I like green veggies as well - including cucumber!

Linda Crampton (author) from British Columbia, Canada on February 23, 2013:

I like green vegetables too, Darknlovely3436, especially broccoli. Thanks for the visit.

Linda Crampton (author) from British Columbia, Canada on February 23, 2013:

Thanks for the comment, nicket!

Annie from NewYork on February 23, 2013:

one of my favorite vegatables.............

nicket on February 23, 2013:

mmmmm very good information, great share!

Mary Hyatt from Florida on February 22, 2013:

Very interesting and informative Hub. Guess we folks just never think of nitric oxide in our bodies. I do love green veggies (except cucumbers!)

Voted Up, etc. and will share.

Linda Crampton (author) from British Columbia, Canada on February 21, 2013:

I hadn't thought of that before! Thanks for the visit, Jimmy.

Jimmy the jock from Scotland on February 21, 2013:

Lol That broccoli looks like David Haslehoff side on.

Linda Crampton (author) from British Columbia, Canada on February 21, 2013:

Thank you very much for the comment, the vote and the share, livingsta! I appreciate them all.

livingsta from United Kingdom on February 21, 2013:

So much useful information which I never knew. Thank you for sharing! Voted up and sharing!

Linda Crampton (author) from British Columbia, Canada on February 21, 2013:

Hi, Peggy. Thanks for the comment and all the votes. The nitric oxide research is exciting. It will be interesting to see how the substance is used in the future!

Linda Crampton (author) from British Columbia, Canada on February 21, 2013:

Thank you the kind comment and the vote, Tom. I appreciate the share, too!

Peggy Woods from Houston, Texas on February 21, 2013:

Hi Alicia,

This is a very interesting article about Nitric Oxide in our bodies. It is good to know some of the natural health benefits and that we can get them from eating our veggies. Also interesting research being done on possible medical applications. It sounds as though much more research needs to be done since there are conflicting conclusions at the current time...but exciting to know. Up, useful and interesting votes.

Thomas Silvia from Massachusetts on February 21, 2013:

Hi my friend great article, was very interesting and informative and so well written. Well done !

Vote up and more !!! Sharing !

Linda Crampton (author) from British Columbia, Canada on February 21, 2013:

Thank you so much for such a lovely comment, Kathi! I appreciate it very much.

Kathi Mirto from Fennville on February 21, 2013:

Your hubs are always so informative and go into depth with added photos and illustrations! Quality information and work! Congrats, Kathi :O)

Linda Crampton (author) from British Columbia, Canada on February 20, 2013:

Thank you, drbj. I would say yes to NO in vegetables! Vegetables are healthy foods for many other reasons, too.

drbj and sherry from south Florida on February 20, 2013:

Fascinating information about nitric oxide, Alicia. Guess I should not say NO to adding more cabbage, beets and broccoli to my diet. Yes?

Linda Crampton (author) from British Columbia, Canada on February 20, 2013:

I wish it were that simple, Deb! Much more research into nitric oxide's behavior is needed, as well as research into the correct amount that is needed for treating health problems. It may be very helpful in the future, though. Thanks for the visit.

Deb Hirt from Stillwater, OK on February 20, 2013:

So nitric oxide introduced into out bodies will help us sleep better, vs. wasting money on sleeping aids, I trust?

Linda Crampton (author) from British Columbia, Canada on February 19, 2013:

Thank you very much for the comment, Martin.

Martin Kloess from San Francisco on February 19, 2013:

Fascinating. Thank you for this.

Linda Crampton (author) from British Columbia, Canada on February 19, 2013:

Thank you for the visit and the comment, Bill. Leafy green vegetables are so healthy - I'm glad that I like them!

Linda Crampton (author) from British Columbia, Canada on February 19, 2013:

Thank you very much, Prasetio. I appreciate your comment and vote, as always!

Bill De Giulio from Massachusetts on February 19, 2013:

Hi Alicia. This was very interesting. I always knew that leafy, green veggies were good for us but I guess I never really knew exactly why and how this all works. Great job explaining all of this.

prasetio30 from malang-indonesia on February 19, 2013:

Very informative and useful for us. Thanks for always renew great information about health. I think we should know about this. Keep it up and my vote always for you. Cheers :-)


Linda Crampton (author) from British Columbia, Canada on February 19, 2013:

I like broccoli too! It's great that it has so many health benefits. Thanks for the comment, Bill.

Bill Holland from Olympia, WA on February 19, 2013:

Although I'm not a big vegetable eater, I do like broccoli, so I'm feeling pretty good about that right now. :) Great information, Alicia. Thanks for making me feel good about my eating habits.