Cranberry is best known to most as an edible fruit, the stuff of jelly and juice, rather than a medicinal herb. However, cranberry juice has evolved, much like Aloe vera, as a quintessential American folk remedy - so well-known in the popular mind as a sure-cure for urinary infections that it prompted scientists to begin to investigate its value more than seventy years ago.

Just What Are Cranberries?

What are cranberries and where do they come from? Depending upon where you live or how you define them, cranberries may come from different plant species. Here in North America, commercial cranberries are the fruits of a tiny bog plant, scarcely a half a foot tall, known to botanists as Vaccinium macrocarpon. The name Vaccinium comes from an ancient Greek word derived from prehistoric Mediterranean languages, referring to berry-producing shrubs. In addition to cranberries, the genus Vaccinium encompasses blueberries, whortleberries, huckleberries, and bilberry. "Macrocarpon" means large fruit.

The native American bog-cranberry (V. macrocarpon) occurs in much of eastern North America in bogs from Newfoundland to Manitoba, south to Virginia, Ohio, and northern Illinois, and locally to the mountains of North Carolina. The designation "large-fruited" cranberry distinguishes our cranberry of the supermarket from the small cranberry V. oxycoccos, a diminutive plant which occurs throughout the northerly regions of the northern hemisphere, notably the north of Europe, but also in North America in bogs south to New Jersey, Pennsylvania and Minnesota. It has considerably smaller fruits, which turn brownish red, and are not as appealing as our common cranberry.

When European settlers first arrived from northern Europe, they were quick to adopt our native V. macrocarpon, with its larger, sweeter fruits, as the cranberry of choice. Hence this species now dominates the market, cultivated on thousands of acres in Massachusetts, Michigan, British Columbia and elsewhere.

A few other plants claim the name "cranberry", including Vaccinium vitis-idaea, known to American botanists as Lingonberry, or mountain cranberry, but to the Swedes, it is cranberry. Cramp-bark, as it is most commonly known in the American market, Viburnum opulus, is sometimes listed as "highbush cranberry", but it is a "cranberry" in name only.

First Observations

Our subject is the common American cranberry. Peter Kalm, an eighteenth century Swedish botanist who conducted extensive botanical explorations of the North American wilderness, described the plant in his 23 February 1749 entry in Travels in North America

"The American cranberry, Vaccinium hispidulum, is extremely abundant in North America and grows in such places as we commonly find our cranberries in Sweden. Those in America are probably bigger, but in qualities so like the Swedish that many people would take them to be just another variety. The English call them cranberries, the Swedes tranbär and the French in Canada atopa, (atocas) which is a name they have borrowed from the Indians. They are brought to market every Wednesday and Saturday at Philadelphia, late in autumn. They are boiled and prepared in the same manner as we do our red lingon, or Vaccinium vitis idaea, and they are used during winter and part of summer in tarts and other kinds of pastry. But as they are very sour, they require a great deal of sugar. That is not very dear, however, in a country where the sugar plantations are near by. Quantities of these berries are sent over, preserved, to Europe and to the West Indies.

Early Medicinal Benefits

Many early travelers, especially hunters and trappers, expressed joy at finding a large bog in the North in the fall months, covered with red cranberries and teaming with wild rice. They were known as a refreshing, invigorating food, which could be dried for winter. Many also reported the fruits to be valuable for staving-off scurvy (vitamin C deficiency), and were useful as a diuretic. One of the most important early nineteenth century writers on American medicinal plants, Constantine Samuel Rafinesque, described medicinal uses for cranberries in 1830.

"The large Cranberries peculiar to America, are the most usually gathered for our markets, and are even exported to Europe and the West Indies: keeping pretty well in barrels, and still better in bottles . . . They are usually as large as cherries, and somewhat similar in shape and color . . . Properties [are] refrigerant, laxative, anti-bilious, anti-putrid, diuretic, sub-astringent, &c. Useful in fevers, diarrhea, scurvy, dropsy, and many other diseases. . . Cranberry tarts are one of the American table luxuries. Their juice mixed with sugar or alcohol keeps a long while, and forms a fine acidulous drink with water, allaying thirst, and lessening the heat of the body."

Cranberries as a Urinary Antiseptic

The diuretic use of cranberries was first reported in a 1787 Latin work on American medicinal plants. A woman with dropsy (water retention) was reportedly cured of dropsy by eating large quantities of the berries. This knowledge trickles down from the eighteenth century literature to become common information on the brink of the twenty first century. Scientific evidence as it relates to the health of the urinary tract was first recognized by German physicians in the mid-1800s. They had observed that after ingesting cranberries, urinary excretion of hippuric acid was increased. This led to the belief that cranberries contained a compound, perhaps benzoic acid, that the body metabolized to produce hippuric acid in the urine. In high concentrations, hippuric acid was believed to have strong antibacterial activity.

Taking this theoretical basis one step further, researchers N. R. Blatherwick and M. L. Long conducted a small human study (involving only two individuals) published in 1923. These scientists attempted to study the ability of cranberries to acidify urine in healthy individuals. The patients were given the same diet for several days. Then one person was given 305 g of cooked cranberries, while the other was given prunes. The urinary pH of the cranberry subject decreased (became more acidic), total acid excretion increased, while concentrations of urinary hippuric acid increased from 0.77 g to 4.74 g.

Despite these findings, in the real world, few people ingest over 10 ounces of cooked cranberries at one sitting. Further studies in the 1950s and 60s gave less convincing results, enhancing cranberry controversies. A 1959 study found that drinking about a gallon of cranberry juice a day (4 L) failed to produce enough hippuric acid excretion to cause antibacterial effects at a pH level of 5. At a somewhat higher pH (5.6) the effectiveness of hippuric acid as an antibacterial was found to decrease by 5-fold. A 1967 study, again, using a small sampling of only 4 to 5 subjects, showed that cranberry juice cocktail (one-third cranberry juice mixed with water and sugar, the typical cocktail of commerce), showed insignificant changes in urinary pH, even after slugging gallons of cranberry juice cocktail for four days. While some studies from the 1920s to the 1970s suggested that urinary acidification was the mechanism by which cranberry juice produced an antibacterial effect in the bladder, other studies conflicted with this theory. Still, the belief that cranberry juice produced urinary antiseptic effects persisted in the popular mind.

New Information - New Hope

Studies in the 1980s began to shed some new light on other possible mechanisms of action that could explain antibacterial effects of cranberry juice, without relating it to urinary acidification and hippuric acid. In 1984 a paper was published in the Journal of Urology and a 1988 Microbios paper showed that when fed to mice, cranberry juice inhibited the adherence of Escherichia coli (the dreaded E. coli of food-gone-bad) to the epithelial cells in mice urinary tracts by 80 percent. Similar activity was found in human subjects as well.

Was a chemical in the juice responsible for the new found E. coli anti-adherence action? The first evidence came in 1989, when an Israeli research group looked at chemical fractions of a number of fruit juices. They found that fructose, a common sugar in many fruit juices, had some anti-adherence effect on the bacterium. They also found that a nondialyzable polymeric compound isolated from cranberry juice (and blueberry juice) had the most potent effect. The evolving theory now became that this compound produced an antibacterial effect in the gut or the bladder by adhering to the tiny hairs of the bacterial surface, thus preventing them from implanting in the tissue mucosal linings, and simply flushing them out of the body via the urine. In 1991 Israeli researchers, publishing in The New England Journal of Medicine, duplicated the previous studies and confirmed the results.

The Clinical Test

While the new pharmacological theories were intriguing, the scientific evidence for the effectiveness of cranberry juice as a urinary antiseptic was scant at best. Clinical trials were uncontrolled, involved a small number of patients, and produced conflicting results. The jury was still out.

A breakthrough in evidence came in a 1994 study published in the Journal of the American Medical Association. A team of researchers associated with Harvard Medical School and various Boston-area hospitals conducted a randomized, double-blind, placebo-controlled study on 153 elderly women volunteers with an average age of 78 and a half years. This patient group was considered appropriate for the study since a large percentage of women over 65 years of age experience at least one urinary tract infection per year.

The study lasted for six months. Volunteers were randomly assigned to consume either 300 mL of cranberry juice cocktail per day or a placebo drink, made to look and taste like cranberry juice, but without cranberry content. The study was designed to measure whether cranberry juice has an effect on bacteriuria (the passage of bacteria in the urine) or pyuria (presence of pus, indicating white blood cells, hence infection in the urine).

The researchers measured baseline urine samples and six clean-voided urine samples collected at one month intervals during the six month duration of the study, looking for bacteria or white blood cells. At the end of the study, the researchers concluded the cranberry juice beverage did indeed reduce the frequency of both bacteriuria and pyuria in elderly women. This study provided the first good clinical evidence in a relatively large sampling of patients, that cranberry juice could be beneficial to the urinary tract.

A recent study suggested that drinking 4 to 6 ounces of cranberry juice daily had a preventative effect for urinary tract infections rather than a curative effect. The study was conducted in elderly patients in nursing homes. Patients were given small amounts of cranberry juice each day for seven weeks. Of the 28 patients monitored, urinary tract infections were prevented in nineteen subjects. The remaining nine patients had significant colony counts of Gram negative bacteria, despite drinking cranberry juice. An additional small study that looked at the use of a cranberry juice concentrate in 800 mg capsules in 21 patients taking 12 capsules a day, found that six of those patients with pre-existing urinary tract infections had no results from the capsules. This led to the conclusion, once again, that cranberry juice cocktail or cranberry concentrates in capsules or tablets may have a better preventative effect for elderly populations, rather than a curative effect. More research is needed.

Adding to cranberry's potential health benefits, a recent study found that an extract of cranberry inhibited an enzyme associated with a reduction in cancer risk.

How to Use Cranberry

Health conscious consumers have come to believe capsulated or tableted cranberry extract products have a distinct advantage over cranberry juice cocktail in that the high levels of added sugar added to cranberry juice are absent from the extracts. Cranberry juice cocktail is a 33% dilution of pure juice with added sugars for flavoring. The extract is available in dietary supplement products as fruit or juice concentrates concentrate in 800 mg capsules. For those who prefer a refreshing beverage, in various studies between 5 to 20 ounces of cranberry juice cocktail daily is considered effective as a preventative for urinary infections. Six ounces of juice is equal to 90 g (about three ounces) of fresh fruit.

No doubt cranberry juice, its extracts and concentrates will continue to attract interest from consumers and scientists alike. Now that it's mechanism of action is better understood, new clinical studies will likely focus on the optimum products and dosage regimes. Now that we can reasonably assume that cranberry works, the question becomes, how does it work best?

References

1. Avorn, J. Reduction of Bacteriuria and Pyuria After Ingestion of Cranberry Juice. Journal of the American Medicinal Association, 1994 271(10)751-754.
2. Blatherwick, N. R., et al. Studies of Urinary Acidity II: The Increased Acidity Produced by Eating Prunes and Cranberries. Journal of Biological Chemistry, 1923, 57:815.
3. Bodel, P. T., et al. Cranberry Juice and the Antibacterial Action of Hippuric Acid. Journal of Laboratory and Clinical Medicine, 1959, 54:881.
4. Bomser, J., et al. "In vitro Anticancer Activity of Fruit Extracts from Vaccinium Species."Planta Medica 1996, 62(3): 212-216.
5. Foster, S. Herbs for Your Health. Loveland, Colorado: Interweave Press, 1996.
6. Kahn, D. H., et al. Effects of Cranberry Juice on Urine. Journal of the American Dietetic Association, 1967, 51:251.
7. Kalm, P. Travels in North America, 2 vols., (reprint of 1770 English edition), New York, Dover Publications, 1966.
8. Ofek, I., et al. Anti-Escherichia Coli Adhesion Activity of Cranberry and Blueberry Juices. New England Journal of Medicine 1991, 324(22):1599.
9. Rafinesque, C.S. Medical Flora : or Manual of the Medical Botany of the United States of North America, Vol. 2. Philadelphia: Samuel C. Atkinson, 1830.
10. Schmidt, D. R. and A. E. Sobota. An Examination of the Anti-Adherence Activity of Cranberry Juice on Urinary and Nonurinary Bacterial Isolates. Microbios 1988, 55:173-181.
11. Sobota, A. E. Inhibition of Bacterial Adherence by Cranberry Juice: Potential Use for the Treatment of Urinary Tract Infections. Journal of Urology, 1984, 131:1013-1016.
12. Zafriri, D., et as. Inhibitory Activity of Cranberry Juice on Adherence of Type 1 and P fimbricated Escherichia Coli to eukaryotic cells. Antimicrobial Agents Chemotherapy 1989, 33:92-98.