Nitric oxide is produced by endothelial cells and is important for regulating blood flow. It acts as a vasodilator to relax smooth muscle cells in blood vessels. The three main types of nitric oxide synthase produce nitric oxide, which has many roles in the body like supporting circulation, immune function, and reproduction. It is involved in processes like maintaining blood pressure and facilitating penile erection. Foods like peppers and dark chocolate contain compounds that can boost nitric oxide levels.