The food industry has done a marvelous job of marketing this small, tartly bittersweet fruit. Cranberry juice and juice blends, dried berries, and other forms are available in nearly every grocery store year-round. Another growing area of consumption is the use of cranberry for various health reasons. Therapeutically, it is touted for everything from UTIs to dental plaque.1, 2 Its potent antioxidant content also makes it popular as a preventive food for maintaining cardiovascular health.

Background

The cranberry is grown in acidic bog soil of the northern United States. The berries, white at first, turn red as they ripen.3 Half of all cranberries grown in the United States come from Wisconsin, with Massachusetts, New Jersey, Oregon, and Washington providing the remainder.1

Indications for use

As mentioned, cranberries have a very high level of antioxidant—1,750 oxygen radical absorbing capacity units (ORACu)/100 g of fresh fruit (ORAC = the ability to subdue oxygen free radicals in vitro).4 Studies show that antioxidants provide protection from atherosclerotic damage and also enhance anti-aging mechanisms.


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The most familiar claim of cranberry’s medicinal efficacy is in the treatment of UTIs. Women throughout the ages have sworn by drinking cranberry juice at the first sign of urinary tract discomfort. Once thought to be an old wives’ tale, science now supports the remedy.

UTIs are responsible for more than 7 million office visits and 1 million hospitalizations every year. This translates into more than $1 billion in annual medical expenses.

Epidemiologically speaking, these simple infections are a tremendous problem for many people. In the United States, 34% of adults over age 20 will have a UTI this year, with 80% of them being women. Of these, 40% will have a recurrence within the year.5

In addition to UTIs, other bacterial infections, such as dental plaque and even peptic ulcer disease caused by Helicobacter pylori, have been shown to respond to the effects of cranberry. Limited information is available on topical uses, but data indicate a benefit in some types of wound healing.

Mechanism of action

The secret to cranberry’s success is the presence of proanthocyanidins (PACs), which are essentially condensed tannins. These chemicals are responsible for an anti-adhesive action that is especially repellent to fimbriated Escherichia coli bacteria.6 This unique property of cranberry PACs makes the mucosal surface too slippery for bacterial attachment. Since E. coli are the predominant bacteria responsible for most uncomplicated UTIs in women, the cranberry-juice remedy seems to have a clinical basis. Cranberry consumption also acidifies the urine, creating an unfavorable environment for bacterial growth.7

While reduction of acute urinary tract symptoms has been noted, an apparent prophylactic effect is even more promising. Participants in one study consumed either a placebo or 300 mL of cranberry juice daily for six months. At the end, the presence of bacteria in the urine was reduced by 75% over placebo, and incidence of acute urinary tract symptoms was decreased by 100% over the length of the study.7

Another potential benefit to the urinary tract is cranberry’s ability to decrease ionized calcium in the urine by nearly 50%, thereby reducing the potential for calcium oxylate renal stone formation.7

The same anti-adhesive effect may be responsible for cranberry’s dental action.2 By preventing microbial colonization in the subgingival tissues, cranberry reduces the formation of plaque.

In the stomach, it is theorized that H. pylori begin growing in the gastric mucosa and, by altering the chemical environment, eventually precipitate duodenal ulcerations. Traditional medicine treats this by controlling the acidity of the environment and using antibiotics. Cranberry acts by preventing the bacteria from gaining the initial foothold.2

Studies are limited but promising. A recent Cochrane review found only two randomized controlled trials involving women, but the results were statistically significant.8 Efficacy in men and children is not substantiated. Studies used an average of 10 oz (300 mL) of juice daily or one to two capsules of powdered extract.

Dosage, safety, contraindications, and drug interactions

Since most store brands of cranberry juice are either sweetened or have the naturally occurring sugar load, diabetics should be counseled regarding management of this carbohydrate intake or advised to purchase sugar-free preparations. No drug interactions have been identified, but some evidence suggests a possible inhibition of the cytochrome P45 2C9 enzyme chain and a potential to increase warfarin effect.8 Gastric upset and occasional diarrhea are potential side effects.8 Occasional food allergies to cranberry have also been noted.

Cost

Capsule formulation cranberry extracts can be very inexpensive, ranging from $8-$12 per month. Drinking 10 oz of juice daily, however, will be more costly, depending on the brand.

Summary

In light of recent fears concerning antibiotic resistance, it makes sense to find other ways to prevent and/or treat bacterial infections. Cranberry is a safe and easy alternative, specifically for UTIs. Individuals prone to these infections ought to consider daily prophylaxis with either cranberry juice or extract. For diabetics who are especially susceptible to these infections, the extracts in capsule form would be the preferred method since it eliminates the carbohydrate load.

References

1. University of Wisconsin-Madison. The American Cranberry. Available at www.library.wisc.edu/guides/agnic/cranberry/faq .htm. Accessed January 5, 2007.

2. National Center for Complementary and Alternative Medicine. Herbs at a Glance. Available at http://nccam.nih.gov/health/cranberry/. Accessed January 5, 2007.

3. Wikipedia. Cranberry. Available at http://en.wikipedia.org/wiki/Cranberry. Accessed January 5, 2007.

4. The Cranberry Institute. Anti-Aging. Available at www.cranberryinstitute.org/health/antiaging.htm. Accessed January 5, 2007.

5. Orenstein R, Wong ES. Urinary tract infections in adults. Am Fam Physician. 1999;59:1225-1234,1237. Available at www.aafp.org/afp/990301ap/1225.html. Accessed January 5, 2007.

6. The Cranberry Institute. The Antiadhesion Properties of Cranberry. Available at www.cranberryinstitute.org/news/ci_antiadhesion_fact_sheet.pdf. Accessed January 5, 2007.

7. Skidmore-Roth L. Mosby’s Handbook of Herbs & Natural Supplements. 3rd ed. St. Louis, Mo.: Elsevier Mosby; 2006:359.

8. Jepson RG, Mihaljevic L, Craig J. Cranberries for preventing urinary tract infections. Cochrane Database Syst Rev. 2000;(2):CD001321.

Ms. Sego is a staff clinician at the Veterans Administration Hospital in Kansas City, Mo., where she practices adult medicine and women’s health. She also teaches at the nursing schools of the University of Missouri and the University of Kansas.