A small glass of 100% fruit juice is a good part of a healthful breakfast, right? If you're on certain prescription medications, your fruit juice may be doing more harm than good.

Grapefruit juice, for example, can interfere with blood pressure medication and actually increase its efficacy, subsequently creating a risk of overdose. Conversely, recent research suggests that grapefruit juice may prevent certain anti-allergy medications from absorbing into the bloodstream properly. A component of grapefruit juice called naringin appears to be the culprit.

Researchers state that this finding may be the "tip of the iceberg" as other juices, including orange and apple, also contain naringin-like substances that may have similar effects.

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If your mom was one to push the orange juice when you were sniffling and sneezing, she may have had good reason.

A review of more than 30 studies shows that taking one 1,000-mg vitamin C supplement per day may help shorten the duration and severity of cold symptoms, especially when you're under stress. You don't need to take a supplement 365 days a year, though, because vitamin C doesn't prevent colds from coming on. It just might help once that cold arrives, though.

There's a lot of speculation about the merits of vitamin C. Some believe in it; some think it's pretty useless. Whatever your view, the current recommended dose of this vitamin is 60 mg daily. One eight-ounce glass of orange juice contains 97 mg.

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