Cranberries are the edible fruits of Vaccinium macrocarpon and its close botanical relative, Vaccinium oxycoccos. V. macrocarpon, indigenous to the northern regions of the United States, is known as the American cranberry. It is sometimes referred to as the trailing swamp cranberry. V. oxycoccos, native to temperate habitats, is actually a subspecies of V. macrocarpon. Since the 1920s, the berries of V. macrocarpon have been used to make traditional cranberry sauce for Thanksgiving.

In the 17th century cranberries were used to treat stomach complaints, liver disorders, blood conditions, vomiting, appetite loss, scurvy, and cancer. While Native Americans made poultices from whole dried berries for wounds, New Englanders employed cranberries in remedies for gallbladder ailments.

In the early 1920s, American scientists discovered that cranberries were an effective herbal treatment for recurrent urinary tract infections (UTIs). Researchers of that era knew that bacteria tend to flourish in an alkaline medium. Consequently, they speculated that an acid environment would kill bacteria. They found that ingesting cranberries increased acidity of urine, creating exactly the type of acid milieux in the intestines that destroyed pathogens. Further investigations revealed that hippuric acid, an active constituent in cranberry, might be responsible for the antibacterial action of cranberries.

Much of the evidence for the antibacterial properties of cranberry was initially anecdotal. Nonetheless, the popularity of cranberry juice for treating UTI and chronic kidney inflammation soared as news of its virtues spread largely by word-of-mouth. By the 1960s, however, researchers concluded that the antibacterial activity of cranberry could not be attributed to acidic urine. A reanalysis of the evidence revealed that at least one quart of cranberry juice would have to have to be consumed at one time to furnish a sufficient amount of hippuric acid to suppress bacteria.

Recent evidence has since shown that cranberry exerts antibacterial effects against the etiologic pathogens of urinary tract infections through other mechanisms. In in vitro and human clinical studies, cranberry was shown to alter the environment of the urinary tract. This renders the bladder and urethra less amenable to bacteria, particularly Escherichia coli, one of the primary bacteria responsible for UTI.

Structure-function relationships have been only partially delineated for cranberry. It contains two constituents that apparently interfere with the capacity of microorganisms to adhere to the epithelial cells lining the urinary tract. One of these active compound is fructose. The other is an unidentified polymeric compound not yet identified.

Native to North America, cranberry is a member of the heath family. It belongs to the genus Vaccinium, which includes 450 circumpolar species of evergreen shrubs. Cranberry is botanically related to blueberry, buckberry, huckleberry, cowberry, and bilberry, all of which are members of Vaccinium. Cranberries resemble uva ursi in their upright branches and tiny dots that speckle the underside of the leaves. However, the leaves of V. macrocarpon contrast with those of uva ursi. Cranberry has characteristically pink flowers, and red-black fruits that appear during June and July. Though edible, the berries are noticeably sour to the palate.

• Fruit

Carbohydrates (e.g., fructose), fiber, polymeric compound of unknown nature, plant acids (e.g., benzoic, citric, malic, and quinic acids).

Available as juice, fresh or frozen berries, cranberry concentrate, fresh berries, dried capsules, and tablets.

Fresh cranberries are usually too sour to consume. Cranberry juice cocktails typically contain sugar, an ingredient known to lower immunity. The addition of sweeteners to cranberry beverages may explain why cranberry juice cocktail and concentrate has not been consistently effective in alleviating symptoms of UTI and bacteriuria.

Traditional use: Stomach complaints, liver disorders, wounds, blood conditions, vomiting, appetite loss, scurvy, and cancer; since the 1920s, it has been a popular folk medicinal treatment in the United states for bladder infections

Conditions: UTIs of the bladder and urethra

Clinical applications: Prevention and treatment of UTI

Several pharmacological investigations support the claim that cranberries and cranberry juice are efficacious in treating UTI. In an in vitro experiment, V. macrocarpon irreversibly inhibited P-fimbrial adhesion of E. coli to growth medium. This may be the same mechanism through which cranberry decreases adherence of E. coli to the mucosal lining of the bladder and urethra in UTI.

The proanthocyanidin fraction of cranberry produced anticarcinogenic effects in in vitro screening assays. In other studies, cranberry juice exhibited anti-adherence effects against E. coli urinary and nonurinary bacterial isolates as well as gram-negative rods found in urine and various clinical specimens.

In a randomized, double-blind, placebo-controlled trial, elderly women were given 300 ml of cranberry juice daily over a six-month period. The plant-derived treatment resulted in a decrease in bacteriuria and pyuria in the test subjects. In another clinical investigation, daily intake of 16 ounces of cranberry juice produced favorable effects in 73% of men and women with UTIs. However, 61% of these positive responders had a recurrence of bladder infection after discontinuing their daily regimen of cranberry juice.

• Juice (containing one-third pure juice): 3 or more fluid ounces per day
• Dried capsules: 6 capsules (equivalent to 3 fluid ounces of cranberry juice cocktail)
• Fresh or frozen cranberries: 1.5 ounces (equivalent to 3 fluid ounces of cranberry juice. 

None reported.

None reported.

No clinically significant interactions between cranberry and conventional medications are known to have been reported in the literature to date.

Cranberry has not been considered by the German Commission E and is not on the General Sale List in Britain.

Ahuja S, Kaack B, Roberts J. Loss of fimbrial adhesion with the addition of Vaccinum macrocarpon to the growth medium of P-fimbriated Escherichia coli. J Urol. 1998;159:559-562

Avorn J, Monane M, Gurwitz JH, Glynn RJ, Choodnovskiy I, Lipsitz LA. Reduction of bacteriuria and pyuria after ingestion of cranberry juice. JAMA. 1994;271:751-754.

Bodel PT, Crotan R, Kass EH. Cranberry juice and the antibacterial action of hippuric acid. J Lab Clin Med. 1959;54:881.

Bomser J, Madhavi DL, Singletary K, Smith MA. In vitro anticancer activity of fruit extracts from Vaccinium species. Planta Med. 1996;62(3):212-216.

Bunney S, ed. The Illustrated Encyclopedia of Herbs. New York, NY: Dorsett Press; 1984:202.

Fleet JC. New support for a folk remedy: cranberry juice reduces bacteriuria and pyuria in elderly women. Nutr Rev. 1994;52(5):168-70.

Grieve M. A Modern Herbal. Vol. I. New York, NY: Dover; 1971:99-100.

Kahn DH, et al. Effect of cranberry juice on urine. J Am Diet Assoc. 1967;51:251.

Mabberley DJ. The Plant-Book: A Portable Dictionary of the Higher Plants. Cambridge, England: Cambridge University Press; 1987:602.

Murray M, Pizzorno J. Encyclopedia of Natural Medicine. 2nd ed. Rocklin, Ca: Prima Publishing; 1998:287-288.

Prodomos PN, Brusch CA, Ceresia GC. Cranberry juice in the treatment of urinary tract infection. Southwest Med. 1968;47:17.

Schlager TA. Effect of cranberry juice on bacteriuria in children with neurogenic bladder. J Pediatr. 1999;135:698-702.

Schmidt DR, Sobota AE. An examination of the anti-adherence activity of cranberry juice on urinary and nonurinary bacterial isolates. Microbios. 1988;55 (224-225):173-181.

Siciliano AA. Cranberry. J Amer Botan Council Herb Res Foundation. Winter 1998;38.

Thomson WA. Medicines from the Earth: A Guide to Healing Plants. Maidenhead, England: McGraw-Hill; 1978:108.

Tyler V. The Honest Herbal: A Sensible Guide to the Use of Herbs and Related Remedies. 3rd ed. Binghamton, NY: Pharmaceutical Products Press; 1993:101-102.

Zafriri D, Ofek I, Adar R, Pocino M, Sharon N. Inhibitory activity of cranberry juice on adherence of type 1 and type P fimbriated Escherichia coli to eucaryotic cells. Antimicrob Agents Chemother. 1989;33: 92-98.