Herbs & Supplements:
Cranberry
Vaccinium macrocarpon

Principal Proposed Uses
  • Bladder Infections (Prevention and Possible Treatment)
Other Proposed Uses
  • Periodontal Disease

The cranberry plant is a close relative of the common blueberry. Native Americans used it both as food and for the treatment of bladder and kidney diseases. The Pilgrims learned about cranberry from local tribes and quickly adopted it for their own use. Subsequent physicians used it for bladder infections, for "bladder gravel" (small bladder stones), and to remove "blood toxins."

In the 1920s, researchers observed that drinking cranberry juice makes the urine more acidic. Since common urinary tract–infection bacteria such as E. coli dislike acidic surroundings, physicians concluded that they had discovered a scientific explanation for the traditional uses of cranberry. This discovery led to widespread medical use of cranberry juice for treating bladder infections. Cranberry fell out of favor with physicians after World War II, but it became popular again during the 1960s—as a self-treatment.

What Is Cranberry Used for Today?

Cranberry is widely used today to prevent bladder infections. Contrary to the research from the 1920s, it now appears that cranberry's acidification of the urine is not likely to play an important role in the treatment of bladder infections; current research has focused instead on cranberry's apparent ability to block bacteria from adhering to the bladder wall.^1–6 If the bacteria can't hold on, they will be washed out with the stream of urine. Interestingly, studies have found that in women who frequently develop bladder infections, bacteria seem to have a particularly easy time holding on to the bladder wall.⁷ This suggests that cranberry juice can actually get to the root of their problem.

Cranberry juice may also be useful for treating or preventing gum disease.⁸

What Is the Scientific Evidence for Cranberry?

Bladder Infection

The best evidence for the use of cranberry juice for preventing bladder infections comes from an unpublished trial presented at the June 2001 meeting of the American Urological Association. This 1-year double-blind placebo-controlled study of 150 sexually active women compared placebo against both cranberry juice and cranberry tablets.⁹ The results showed that both forms of cranberry significantly reduced the number of episodes of bladder infections.

Another double-blind study evaluated cranberry juice cocktail for treatment of chronic bladder infections.¹⁰ This trial followed 153 women with an average age of 78.5 years for a period of 6 months. Many women of this age group have what are called chronic assymptomatic bladder infections: signs of bacteria in the urine without any symptoms. Half of the participants were given a standard commercial cranberry cocktail drink, the other a placebo drink prepared to look and taste the same. Both treatments contained the same amount of vitamin C to eliminate the possible antibacterial influence of that supplement. Despite the weak preparation of cranberry used, the results showed a 58% decrease in the incidence of bacteria and white blood cells in the urine.

A double-blind placebo-controlled study evaluated the effectiveness of cranberry extract in children with bladder paralysis (neurogenic bladder) who needed to use a catheter.¹¹ The results showed no benefit.

Finally, a year-long open trial of 150 women found that regular use of a cranberry juice/ligonberry combination reduced the rate of urinary tract infection as compared to a probiotic drink or no treatment.¹² However, because this study was not double-blind, the results are unreliable.

Gum Disease

Preliminary evidence suggests that cranberry juice might be useful for treating or preventing gum disease.¹³ However, there is one kink to work out before cranberry could be practical for this purpose: the sweeteners added to cranberry juice aren't good for your teeth, but without them cranberry juice is very bitter.

Dosage

The proper dosage of dry cranberry juice extract is 300 to 400 mg twice daily. For people who prefer juice, 8 to 16 ounces daily should suffice. Pure cranberry juice, not sugary cranberry juice cocktail with its low percentage of cranberry, should be used for best effect.

Safety Issues

There are no known risks of this food for adults, children, or pregnant or nursing women. However, cranberry juice may allow the kidneys to excrete certain drugs more rapidly, thereby reducing their effectiveness. All weakly alkaline drugs may be affected, including many antidepressants and prescription painkillers. In addition, indirect evidence suggests that regular use of cranberry concentrate tablets might increase risk of kidney stones.¹⁴

Interactions You Should Know About

If you are taking weakly alkaline drugs, which include many antidepressants and prescription painkillers, cranberry might decrease their effectiveness.

Last reviewed July 2002 by Medical Review Board

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