Niacin

Daily Value: 20 milligrams

Good Food Sources: Chicken breast, tuna, veal, fortified breads and cereals

The niacin story is one of triumph and potential tragedy. The triumph: One form of niacin, nicotinic acid, dramatically lowers the risk of heart disease at a fraction of the cost of prescription drugs. The tragedy: Used improperly, slow-release niacin can cause severe side effects, including liver damage.

"In the right hands, it's a very useful medication. It lowers harmful cholesterol and raises good cholesterol better than any drug we have," says James McKenney, Pharm.D., professor in the School of Pharmacy at Virginia Commonwealth University Medical College of Virginia in Richmond. "But taken indiscriminately by an uninformed person without a professional monitoring his condition, it can be dangerous."

Although more research needs to be done, it's thought that niacin somehow limits the liver's ability to produce cholesterol.

A less controversial use of niacin has no less positive results. Niacin prevents pellagra, a now rare condition that often starts with skin inflammation, includes diarrhea and depression and ends in death. In the deep South at the turn of the century, this ailment afflicted over 100,000 people, largely because their diets consisted mainly of cornmeal.

Not only does corn contain a form of niacin that the body cannot readily use, but a diet consisting of nothing but corn can also create an amino acid imbalance, says Marvin Davis, Ph.D., chairman of the Department of Pharmacology at the University of Mississippi at Oxford.

Thanks to the fortification of flours and cereals with niacin, pellagra is rare in all but alcoholics and people suffering from severe gastrointestinal problems, says Dr. Davis.

Niacin supplements may also reduce the incidence of asthma-induced wheezing, perhaps because this nutrient prevents the release of histamine, a biochemical normally released during allergic reactions. Harvard University researchers found that people who got the most niacin in their diets were significantly less likely to have bronchitis or wheezing than people who got the least. Lower blood levels of niacin were also linked to increased wheezing.

Using Niacin Safely

It's virtually impossible to get too much niacin in your diet. But when you take niacin supplements in the doses needed to improve your cholesterol levels, you are likely to experience side effects ranging from flushing, itching and excessive nervousness to headaches, intestinal cramps, nausea and diarrhea. And high doses of niacin, especially the slow-release form, can cause liver damage. That's why this kind of therapy needs to be taken under medical supervision.

Niacinamide, a form of niacin that is included in