July 24, 2020 5 min read

What is Nitric Oxide?

Nitric Oxide is a colorless gas and a chemical compound with the chemical formula of NO. In mammals, including humans, this gaseous molecule acts as a biological messenger in many physiological and pathological pathways and carries out significant processes like vasodilation in the way. Inside the body, it is biosynthesized from arginine, oxygen, and NADPH via NO synthesizing enzymes.

How does it work? Mechanism and characteristics

Biochemically, it binds with the heme moiety of cytosolic guanylate cyclase, activating the guanylate cyclase enzyme and increasing intracellular levels of cyclic guanosine monophosphate (cGMP). Increased levels of cGMP cause relaxation of the smooth muscles and also leads to vasodilation. Vasodilation is the most important function of NO because dilated vessels mean oxygen and nutrients are being delivered more efficiently and effectively to all systems of the body. Many chronic conditions like heart diseases and type 2 diabetes and also erectile dysfunction has been associated with a limited capacity of producing NO at a molecular level. 

Nitric oxide has an attribute of diffusing freely across membranes. It is because of this property that the molecule is also ideal for paracrine and autocrine signaling. These signaling pathways result in the secretion of important hormones like insulin and growth hormone.

Biological Functions of Nitric Oxide

Effect on Cardiovascular System

Nitric Oxide is known as the Endothelial Derived Relaxing Factor (EDRF). By dilating the blood vessels and increasing the blood flow, it decreases the blood pressure and the strain on the heart caused by it. Especially important is the raised blood pressure in pregnant women (preeclampsia) which is fatal to both the mother and the baby, which is also meticulously regulated and controlled by this compound. NO also acts directly on the cardiac muscles and decreases its contractility, ergo the heart rate. By constant signaling and regulation, it has become crucial to both the heart and blood vessels especially the inner lining of the blood vessels called the endothelium. Endothelium directly takes part in the production of the NO which conversely not only widens the vessels but also reduces inflammation and hypoxic stress in the vessel walls. It has also been made evident by constant research that by doing this, NO prevents the diseases of the vessels of the heart (coronary artery diseases) significantly which is closely tied to the mechanism of impaired NO synthesis. Given how prevalent the coronary heart diseases are, how more of an important molecule does it have to be for the body? 

Effect on Smooth muscles

Walls of the gastrointestinal tract and the erectile tissue are all made up of the involuntary smooth muscles. Nitric oxide dilates blood vessels, increasing the blood supply to this type of muscle. This consequently protects the walls and keeps them intact and healthy. This same phenomenon of vasodilatation and smooth muscle relaxation comes into action during the erection of the penis. 

Effect on the Immune System

Nitric oxide is released as free radicals by the phagocytes during an immune response. Phagocytes are the frontline army fighting against the disease-causing microbes and the nitric oxide produced is toxic for the bacteria as well as some parasites. Some examples of microorganisms that NO actively works against to destroy are Leishmaniasis and Malaria. It causes damage by destroying the DNA structures of these organisms and degradation of the iron-sulfur centers within them strengthening the immune system. 

Effect on Erectile Dysfunction

Erectile dysfunction (ED) is a disorder that involves the inability to achieve or maintain an erection. Nitric oxide is required for the smooth muscles of the penis to relax, which is important for the engorgement of the chambers inside the penis. Nitric oxide boosting supplements that contain L-citrulline (viagra) have proved to be the treatment for this dysfunction which stresses its importance.   

Effect of type 2 diabetes mellitus

Impairment of Nitric oxide production and hence its low levels have been implicated in the damage to vessels caused during Type 2 Diabetes Mellitus. A wide range of studies has proven that increasing the optimum level of NO via supplementation has increased insulin sensitivity in people suffering from diabetes type 2. This has allowed for better control of glucose levels in the blood. In the long run, this delays the progression and long term complications of the disease. 

Other outcomes

It has also been postulated that vasodilation and better oxygenation and nutrition transport nitric oxide improves physical endurance and betters the athletic performance and stamina in sports. This has also reduced the muscle soreness post workouts. Since it increases oxygen delivery to the muscles and skin, nitric oxide also speeds up the healing process.

How to maintain good levels of NO inside the body?

It is because of all the above mentioned integral biochemical processes inside the body that NO takes part in that it is important to maintain an optimum NO level at all times. Nitric oxide is naturally produced inside the human body however, there are some non-modifiable factors like increasing age that reduce the overall rate of NO production. As the body ages, the enzymes that are involved in NO synthesis start wearing out and deactivating, this lowers the NO level significantly. A poor diet and lack of exercise also decrease the levels. Less significant habits that prevent us from reaching optimal levels include the use of mouthwashes. Mouthwash is potent antiseptics that kill the good bacteria inside the human mouth. These bacteria are directly involved in generating NO from dietary nitrate. These factors affect the endogenous pathways of NO biosynthesis which brings in the desperate need for lifestyle changes and NO supplementation. 

Firstly, the natural way of restoring the NO inside the body is taking green leafy vegetables like celery, lettuce, and beetroot which are rich in nitrates and nitrites. Exercise is another lifestyle adaptation thought to be a very productive way of maintaining a level of NO. It not only stimulates the production of NO but also ensures the health of vessel walls - the benefit is double layered especially in cardiovascular disease prevention.

Another promising way of improving NO inside the body is supplementation. These supplements are called NO boosters because they contain ingredients like L-arginine and L-citrulline that speeds up NO synthesis inside the body instead of NO itself. 


Over the decades, promising evidence has been brought forward to indicate that the importance of nitric oxide as a mediator can not be ignored. Its role in many prime processes inside the human body, especially as a vasodilator has made it abundantly clear that its optimum level should be maintained constantly.

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