Q. Does the immune booster Airborne prevent or cure colds?

A. After catching a cold over the holidays that lingered for days, I wished there were a magic potion to make it disappear. Although some people insist that Airborne keeps them from getting colds, this product's effectiveness has not been studied by reputable scientists.

Airborne contains a blend of herbs, vitamins and minerals. Only three of Airborne's ingredients have been studied in relation to colds, all with mixed results. They are vitamin C, zinc and echinacea.

Vitamin C has long been promoted as both a preventive measure and a cure for colds. Contrary to popular belief, vitamin C cannot prevent you from getting a cold, not even in high doses. Some research suggests that taking vitamin C at the first sign of a cold may decrease the severity and duration of a cold. Other studies show no change. Doses in excess of 2,000 milligrams daily may cause nausea and diarrhea.

The mineral zinc, available in lozenges, nasal sprays and gels, may work by preventing the formation of proteins needed by a cold virus to reproduce. Study results are mixed. An analysis of several studies found only weak evidence of the effectiveness of zinc lozenges in reducing cold duration.

The herbal supplement echinacea also sparks controversy among experts. A recent analysis of 14 studies found that taking echinacea reduced the odds of developing a cold by 58 percent. It also reduced the duration of colds by a day and a half. The researchers concluded that echinacea may help decrease the severity of cough, headache and nasal congestion symptoms.

These findings contradict a 2005 University of Virginia study that found echinacea had no effect on how often participants caught colds or on the severity of their symptoms.

A healthy lifestyle can improve your odds in the fight against colds. A healthy diet, stress reduction and exercise increase the body's natural virus-killing cells. Several studies show exercise promotes fewer and less intense bouts with colds.

Cold viruses linger on objects like telephones, TV remotes, and door handles for many hours. During cold season, washing your hands after touching these objects is your best defense. Hand-washing destroys most viruses.

Whether Airborne or other supplements will prevent or shorten a cold any better than lifestyle changes and frequent hand washing is open to debate. There is no cure for the common cold.

Amy Tousman is a registered dietitian and certified diabetes educator with Nutrition Unlimited in Kailua. Hawai'i experts in traditional medicine, naturopathic medicine and diet take turns writing the Prescriptions column. Send your questions to: Prescriptions, Island Life, The Advertiser, P.O. Box 3110, Honolulu, HI 96802; islandlife@honoluluadvertiser.com; or fax 535-8170. This column is not intended to provide medical advice.