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Cranberries are a traditional part of the Thanksgiving feast in America, where V. macrocarpon is part of the native flora. Recent interest in cranberries, however, goes beyond sauce or relish.

A traditional women’s belief (or old wives’ tale) that cranberry juice can be beneficial for urinary tract infections was discounted by doctors until a study was published in the Journal of the American Medical Association in 1994. Score one for the old wives!

This placebo-controlled, double-blind trial showed that drinking cranberry juice cocktail definitely reduced elderly women’s risk of urinary tract infection. Ocean Spray provided both the cranberry juice and the look-alike, taste-alike, cranberry-free placebo juice.

Cranberries are too tart to be palatable without sweetening, but cranberry juice cocktail products have become quite popular.

Some people concerned about their intake of sugar have turned to dried cranberry capsules, although there are no studies yet to confirm that these are equally as active as juice.

The part of the plant that is used is the berry.

Active Ingredients

Cranberries are very rich in anthocyanins. They also contain fructose (fruit sugar) and small amounts of vitamin C and fiber.

Other constituents include catechins and triterpenoids, as well as malic, citric, and quinic acids.

Cranberry also contains an unidentified factor that counteracts bacterial chemicals known as adhesins.


The principal use of cranberry juice is to prevent urinary tract infections. The antiadhesin activity of cranberry juice seems to keep bacteria from getting a foothold in the lining of the urinary tract.

Some women claim that drinking large quantities of cranberry juice at the first symptoms of cystitis can stop an infection. In most instances, though, once an infection has begun and is causing pain and urgent urination, it requires medical treatment.

Cranberry juice has been used infrequently in conjunction with antibiotics to treat chronic kidney inflammation.

Cranberry juice has also been used in nursing homes to keep the urine of incontinent patients from developing an unpleasant ammonia-like smell. Evidently cranberry juice is able to inhibit the growth of the bacteria that degrade urine to ammonia.

Test tube research at the University of Wisconsin suggests that cranberry juice may help keep LDL cholesterol from oxidizing. If confirmed, this activity would help prevent the development of cholesterol plaques in arteries.


The dose used in the double-blind prevention trial mentioned above was 300 ml (approximately 10 fluid ounces) per day. In acute urinary tract infections, up to 32 fluid ounces daily may be consumed.

Special Precautions

No special precautions have been noted with cranberries. Diabetics may need artificially sweetened juice, as the usual cranberry juice cocktail is high in sugar.

Adverse Effects

Diarrhea may occur, but it has been reported only with the consumption of a large quantity of juice (roughly 3 to 4 quarts).

Possible Interactions

Although cranberry juice contains some tannins, it has not been reported to interfere with the absorption of iron supplements or other minerals.

In older people with too little stomach acid or in patients taking strong acid suppressors such as Prilosec, vitamin B12 absorption may be impaired. Cranberry juice appears to improve the absorption of this crucial vitamin in such cases.

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About the Author
Joe Graedon is a pharmacologist who has dedicated his career to making drug information understandable to consumers. His best-selling book, The People’s Pharmacy, was published in 1976 and led to a syndicated newspaper column, syndicated public radio show and web site. In 2006, Long Island University awarded him an honorary doctorate as “one of the country's leading drug experts for the consumer.”.
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