Cold remedies with conflicting evidence

In spite of ongoing studies, the scientific jury is still out on some popular cold remedies, such as vitamin C and echinacea. Here's an update on some common alternative remedies:

• Vitamin C. It appears that taking vitamin C won't usually help the average person prevent colds.

  However, some studies have found that taking vitamin C before cold symptoms start may shorten the length of time you have symptoms. Vitamin C may benefit people at high risk of colds due to frequent exposure — for example, children who attend group child care during the winter.

• Echinacea. Study results on whether echinacea prevents or shortens colds are mixed. Some studies show no benefit. Others show some reduction in the severity and duration of cold symptoms when taken in the early stages of a cold. Different types of echinacea used in different studies may have contributed to the mixed results.

  Echinacea seems to be most effective if you take it when you notice cold symptoms and continue it for seven to 10 days. It appears to be safe for healthy adults, but it can interact with many drugs. Check with your doctor before taking echinacea or any other supplement.

• Zinc. Several studies have suggested that zinc supplements may reduce the length of a cold. But research has turned up mixed results about zinc and colds.

  Some studies show that zinc lozenges or syrup reduce the length of a cold by about one day, especially when taken within 24 to 48 hours of the first signs and symptoms of a cold.

  Zinc also has potentially harmful side effects. Talk to your doctor before considering the use of zinc to prevent or reduce the length of colds.