Cranberry juice can be an effective preventative for urinary tract infections.
Cranberries can work as a preventative for urinary tract infections.
A supplement to the Herb Companion from the American Botanical Council and the Herb Research Foundation.
In addition to being a tangy, refreshing beverage, cranberry juice cocktail is a time-honored American folk remedy for urinary tract infections, a disorder that is especially common in women. Its reputation has been upheld, at least in part, by a host of scientific studies.
The native American cranberry (Vaccinium macrocarpon) is a mat-forming evergreen shrub of the heath family (Ericaceae) that grows in bogs from Newfoundland to Manitoba south to Virginia, Ohio, and northern Illinois. Most Americans are familiar with its glossy red fruits, up to 3/4 inch across, that seem to materialize in grocery stores just before Thanksgiving. This species is cultivated on thousands of acres of artificial bogs in Massachusetts, Michigan, Wisconsin, and British Columbia.
Several other species are also known as cranberries. The closely related European cranberry (V. oxycoccos), which occurs in northern North America and Asia as well as in Europe, has much smaller, brownish red berries. It is not cultivated. Mountain cranberry (V. vitis-idaea), or lingonberry, is cultivated to a limited extent in Europe, and its small fruits are also collected from the wild. The bark of highbush cranberry (Viburnum trilobum and V. opulus), medium-sized shrubs of the honeysuckle family (Caprifoliaceae) with small, extremely astringent red fruits, has been used by herbalists and Native Americans to treat menstrual cramps.
Early white settlers valued cranberries as a refreshing, invigorating food that was easily dried for winter storage. They also discovered that eating the fruits prevented scurvy (vitamin C deficiency) and relieved dropsy (fluid accumulation in connective tissue) by promoting urination. Fevers, diarrhea, and many other disorders were treated by ingesting cranberries, and the crushed berries were poulticed on tumors and wounds.
German physicians in the mid–nineteenth century observed that ingesting European cranberries increased the excretion of hippuric acid in the urine. Further, a 1923 study reported that the urine of a subject given 305 g (more than 10 ounces) of cooked cranberries became more acidic, with a sixfold increase in the concentration of hippuric acid, whereas that of a subject given prunes didn’t change. Because acid inhibits the growth of bacteria, this finding was thought to indicate that eating cranberries would inhibit the growth of bacteria in the urinary tract (the bacterium Escherichia coli, which is found in the intestinal tract of even healthy individuals, is the cause of most urinary tract infections).
Tests of this theory produced conflicting results. A 1959 trial found that drinking 4 liters (more than a gallon) of cranberry juice a day failed to produce enough hippuric acid to inhibit bacterial growth, and a four-day study of four subjects in 1967 showed that drinking gallons of cranberry juice cocktail (33 percent sweetened cranberry juice) produced insignificant changes in urinary pH. Still, some women with recurrent infections continued to drink cranberry juice, and at least some of them were convinced that it brought relief.
Studies in the 1980s on mice and later on humans discovered that urine acidity was not the mechanism by which cranberry affects urinary tract infections. Instead, researchers found that cranberry juice inhibits the growth of E. coli bacteria by preventing their attachment to cells lining the urinary tract, where they would otherwise multiply and cause infection. A 1989 study showed that fructose, a common sugar in many fruits, had some ability to keep bacteria from attaching, but that a compound isolated from cranberry and blueberry juice had the most potent effect. The bacteria are simply flushed away in the urine.
In the past few years, several studies have reexamined cranberry juice’s effect on urinary tract infections. A randomized, double-blind, placebo-controlled study published in 1994 involved 153 elderly women who had had at least one urinary tract infection a year. For six months, the subjects consumed either 300 ml (11/4 cups) of cranberry juice cocktail per day or a placebo. Urine samples were collected at one-month intervals from each subject. The researchers concluded that the cranberry juice beverage reduced the number of bacteria in the urine as well as the frequency of infection.
In another study, twenty-eight nursing-home patients prone to frequent urinary tract infections were given 4 to 6 ounces (1/2 to 3/4 cup) of cranberry juice cocktail daily for seven weeks. Nineteen subjects had no further infections during the study. The remaining nine had significant bacteria counts that seemed unresponsive to cranberry, leading researchers to suggest that cranberry acts as a preventive, not a cure. A further study of twenty-one patients found that taking twelve 800 mg capsules of cranberry juice concentrate a day did not help six of the patients who had preexisting urinary tract infections.
Between 5 and 20 ounces (5/8 and 21/2 cups) of cranberry juice cocktail daily is considered effective for preventing urinary tract infections. Six ounces of juice is equivalent to 90 g (about 3 ounces) of fresh fruit. Individuals concerned about the sugar in cranberry juice cocktail can find artificially sweetened cocktails in supermarkets and unsweetened juice in health-food stores. Cranberry extracts in 800 mg capsules or tablets are sold as dietary supplements. Follow label guidelines. It is likely that further clinical studies will focus on the form and dosage of cranberry that best prevent infections.
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Blatherwick, N. R., and M. L. Long.“Studies of Urinary Acidity II: The Increased Acidity Produced by Eating Prunes and Cranberries.” Journal of Biological Chemistry 1923, 57:815–818.
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Schmidt, D. R., and A. E. Sabota. “An Examination of the Anti-adherence Activity of Cranberry Juice on Urinary and Nonurinary Bacterial Isolates.” Microbios 1988, 55:173–181.
Zafriri, D., et al. “Inhibitory Activity of Cranberry Juice on Adherence of Type 1 and P fimbriated Escherichia coli to Eukaryotic Cells.” Antimicrobial Agents Chemotherapy 1989, 33:92–98.
“Herbs for Health” is offered bimonthly by the American Botanical Council and the Herb Research Foundation as a supplement to The Herb Companion. Editor, Steven Foster.
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“Herbs for Health” is intended as an educational service, not a source of medical advice or a guide for self-medication. Please consult a qualified health-care professional for treatment of any serious health problems. For further information on any of the topics in “Herbs for Health”, write the
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