Nitric Oxide: The New Hero of Human Biology

Twenty minutes on a treadmill will certainly help you fit into that one-size-too-small dress. But new research suggests that exercise may also help increase the production of nitric oxide, a substance that does a variety of important jobs in the body, perhaps none more valuable than to help prevent heart disease.

"Nitric oxide does a variety of jobs," explains Dr. Jason Allen of Duke University. "It tends to be antiatherogenic, which means that it helps prevent your arteries from becoming clogged. From start to finish, this is a 40-year process which depends on lifestyle." That is, it's a function of what you eat, how you exercise, and the stresses you are under.

Allen and colleagues have been studying the production of nitric oxide synthase, the enzyme that is responsible for producing nitric oxide. They have found that exercise increases production of the enzyme, which then increases the chances that the nitric oxide levels in the blood will increase and protect the artery lining.

The Duke researchers' first report, which was released in November 2003, found that exercise especially helped those people who were labeled "at-risk" for heart disease. In blood samples taken after exercise, they had an "almost doubling of the brachial artery reactivity," said Allen. This means that while exercise is beneficial for everyone, those with more risk factors may get extra benefit from exercise.

In terms of biology, it works like this: Extra time on the stairmaster helps boost the nitric oxide levels in the endothelium, the lining of artery walls. One of the initial effects of arteriosclerosis is damage to that lining, which exposes the vessels to harmful circulating cells. Nitric oxide released by the endothelium works to prevent red blood cells from sticking together, or aggregating, and attaching to the vessel wall. It can also work to control vascular tone, allowing the arteries to relax and stay clear.

Nitric oxide is now one of the heroes of human biology. But that wasn't always the case. Until recently, nitric oxide was best known as that nasty smog-producing stuff that comes out of tailpipes. Then along came three scientists -- Louis Ignarro, Robert Furchgott and Ferid Murad -- whose pioneering work showing the good side of nitric oxide won them a Nobel Prize.

The scientists were the first to identify the artery-dilating properties of nitric oxide. Specifically, they identified the following process: the innermost layer of cells (called the endothelium) releases nitric oxide when triggered by the enzyme nitric oxide synthase. Nitric oxide then sends a signal to the inner smooth-muscle cells of artery walls prompting them to dilate (relax). The artery walls relax and blood pressure eases, thus increasing the blood flow in the arteries. Extra time at the gym helps this process even more, by increasing the amount of nitric oxide that enters the bloodstream.

Scientists have taken this preliminary research and run with it in different directions. Probably the best known is Viagra. The drug increases the levels of nitric oxide and promotes smooth muscle relaxation. This, in turn, allows for extra blood flow to the penis, leading to erection.

Other nitric oxide-based products have made their way onto the market. Some are dietary supplements, such as Niteworks, a citrus-flavored powder developed by Herbalife and Ignarro. "We've done a lot of work to show that one does not have to take prescription drugs to be effective in treating cardiovascular disease," says Ignarro. One can just engage in natural sorts of things -- dietary supplements, exercise, diets that are low in fat, and so on. All of these things increase or enhance nitric acid production in the body; and the more nitric oxide that is produced, the more protection you have against cardiovascular disease."

Researchers are continuing to study the possible uses of nitric oxide and its link to heart disease prevention. In the meantime, scientists recommend that you maximize nitric oxide production in your body by following routines that hopefully are already familiar to you: a low-fat diet, mild to moderate exercise, smoking cessation and better "cellular nutrition." This includes consuming antioxidants like vitamins A and C, which prevent the breakdown (oxidation) of nitric oxide in the body. And popping a few extra vitamin Cs during this time of year certainly can't hurt.