Nitric oxide, not to be confused with laughing gas (which is nitrous oxide), is important for the health of the cardiovascular system, the joints, the lung, the nervous system, the immune system and may even be useful in preventing erectile dysfunction. It is synthesized from L-arginine.

In the journal Arthritis and Rheumatism (August 1993;36(8):1036-1044), an article appeared that reviewed the role nitric oxide plays in joint health. Chondrocytes produce a form of nitric oxide synthase, which forms nitric oxide from L-arginine.

The vascular endothelium produces nitric oxide, which relaxes the blood vessels and improves blood flow. It acts on the autonomic nervous system, through efferent nerves. It can suppress the initial formation of atherosclerosis lesions. It inhibits platelet adhesion and aggregation, suppressing thrombosis, according to an article appearing in The New England Journal of Medicine (July 27, 1995;333(4):251-253). According to an article in The Lancet (Sept 27, 1997;350:901-902) states that in patients with high cholesterol, supplementation with L-arginine improves the health of the endothelium.  That article also states that nitric oxide is a powerful vasodilator and inhibits plaque formation.

Also in The New England Journal of Medicine (July 27, 1995;333(4):214-221) is a study that  looked at nitric oxide synthase in the lung endothelia of 22 patients with plexogenic pulmonary arteiopathy, and 24 patients with seconday pulmonary hypertension and compared it to 22 controls. The study found that pulmonary hypertension is associated with low nitric oxide synthase activity.  L-arginine supplementation has been show to reduce pulmonary pressure in patients with pulmonary hypertension. Another article in the same issue states that earlier animal studies on pulmonary hypertension have shown that supplementing with L-arginine improves vasodilation.