Overview
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. Physicians later 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. Because bacteria that commonly affect the urinary tract, such as Escherichia coli, dislike acidic environments, 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.
Uses and Applications
Cranberry is widely used today to prevent bladder infections, although the evidence to support this use remains limited. 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 study has focused instead on cranberry’s apparent ability to block bacteria from adhering to the bladder wall. If the bacteria cannot “hold on” to the wall, they will be washed out with the stream of urine. 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. This suggests that cranberry juice can actually get to the root of the problem.
Just as cranberry seems to prevent adhesion of bacteria to the bladder,
preliminary evidence suggests that it might also help prevent adhesion of the
ulcer-causing bacterium Helicobacter pylori to the stomach wall.
On this basis, it has been proposed for preventing or treating ulcers, with
mixed results.
Other preliminary evidence suggests that the same actions of cranberry juice
might make it useful for treating or preventing cavities or
gum
disease. However, there is one problem to work out before
cranberry could be practical for this purpose: The sweeteners added to cranberry
juice harm teeth, but without sweeteners, cranberry juice is very bitter.
Cranberry has also been investigated as a possible aid in reducing the risk of
heart
disease and cancer and as a treatment for diabetes, but there
is no meaningful evidence that it is actually helpful for these conditions.
Another study failed to find cranberry significantly effective for enhancing
mental function.
Scientific Evidence
Bladder infection. Probably the best evidence for the use of cranberry juice for preventing bladder infections comes from a one-year, double-blind, placebo-controlled study of 150 sexually active women that compared placebo with both cranberry juice (8 ounces three times daily) and cranberry tablets. The results showed that both forms of cranberry significantly reduced the number of episodes of bladder infections; cranberry tablets were more cost-effective.
A double-blind study of 376 hospitalized elderly people attempted to determine whether a low dose of cranberry juice (as cranberry juice cocktail, 10 ounces daily–a very low dose in comparison to the previous study) would help prevent acute infections. It failed to find benefit, perhaps in part because of the dosage of cranberry and because of the low number of infections that developed overall.
Another double-blind study evaluated cranberry juice cocktail for the treatment
of chronic bladder infections. This trial followed 153 women with an average age
of 78.5 years for six months. Many women of this age group have chronic
asymptomatic bladder infections: signs of bacteria in the urine without any
symptoms. One-half of the participants were given 10 ounces a day of 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 percent decrease in
the incidence of bacteria and white blood cells in the urine.
A one-year-long open trial of 150 women found that the regular use of a cranberry juice and lingonberry combination reduced the rate of urinary tract infection compared with a probiotic drink or no treatment. However, because this study was not double-blind, the results are unreliable.
A review of ten studies investigated the benefits of cranberry juice or tablets, compared with a placebo control, in persons susceptible to urinary tract infections. Among 1,049 participants, researchers found that the cranberry products reduced the incidence of urinary tract infections by 35 percent, a statistically significant amount, in a twelve-month period. The effect was most notable in those with recurrent infections. However, many participants dropped out of the studies early, suggesting that continuous consumption of cranberries is not well tolerated.
On the negative side, three other double-blind, placebo-controlled studies evaluated the effectiveness of cranberry extract for eliminating bacteria in the urine of people with bladder paralysis (neurogenic bladder). The results showed no benefit. However, a subsequent study of forty-seven persons with neurogenic bladder from spinal cord injuries found that the use of cranberry extract tablets for six months significantly reduced the risk of urinary tract infections.
Ulcers. The bacterium H. pylori plays a major
role in the initiation and maintenance of peptic
ulcers, those ulcers in the stomach and duodenum. A ninety-day,
double-blind, placebo-controlled study performed in China tested the effects of
daily consumption of cranberry juice in persons who were chronically infected with
H. pylori (but who did not necessarily have ulcers). The
results indicated that the use of cranberry significantly decreased levels of
H. pylori in the stomach, presumably by causing some of the
detached bacteria to be “washed away.” Another study involving 295 children with
H. pylori but without ulcer symptoms also demonstrated the
ability of cranberry to reduce the levels of the stomach bacteria.
While this was a promising finding on a theoretical level, it did not directly address the treatment or prevention of ulcers.
A more practical study evaluated the use of cranberry as a support to standard therapy. This double-blind trial enrolled 177 people with ulcers who were undergoing treatment with a common triple-drug therapy (omeprazole, amoxicillin, and clarithromycin, known as OAC) used to eradicate H. pylori. All participants received this drug treatment for one week. During this week and for two weeks after, they were additionally given either placebo or cranberry juice. Researchers also looked at a third group attending the same clinic, who received only OAC.
The results were somewhat promising. In the study group at large, OAC plus cranberry was no more effective than OAC plus placebo or OAC alone. However, among female participants in the study, the use of cranberry was associated with a significantly increased rate of H. pylori eradication compared with placebo or no treatment.
Does this mean that women undergoing ulcer treatment may benefit from cranberry? Perhaps, but not necessarily. When a treatment fails to produce benefit in the entire group studied, researchers may, after the fact, look for a subgroup who did benefit. The laws of chance alone ensure that they can almost always find one. Therefore, it is not clear whether cranberry actually did provide benefit or whether this finding was merely a statistical fluke.
Dosage
The usual dosage of dry cranberry juice extract is 300 to 400 milligrams twice daily, and the usual dosage of pure cranberry juice (not cranberry juice cocktail) is 8 to 16 ounces daily.
Safety Issues
As a widely consumed food, cranberry is thought to have a generally good safety
profile. However, several case reports suggest that cranberry could interact with
the drug warfarin (Coumadin), potentially leading to internal
bleeding. Two formal studies have failed to find evidence of such an interaction,
while a third study did find that cranberry can increase the blood thinning effect
of warfarin in healthy male participants. One should take caution, especially when
consuming more than 8 ounces of cranberry juice daily.
In addition, cranberry juice might allow the kidneys to excrete weakly alkaline
drugs more rapidly, thereby reducing their effectiveness. This would include many
antidepressants and prescription painkillers. Finally,
indirect evidence suggests that the regular use of cranberry concentrate tablets
might increase the risk of kidney stones.
Important Interactions
For persons taking warfarin, the use of cranberry might lead to excessive bleeding. Cranberry could decrease the effectiveness of drugs that are weakly alkaline, including many antidepressants and prescription painkillers.
Bibliography
Chambers, B. K., and M. E. Camire. “Can Cranberry Supplementation Benefit Adults with Type 2 Diabetes?” Diabetes Care 26 (2003): 2695-2696.
Gotteland, M., et al. “Modulation of Helicobacter pylori Colonization with Cranberry Juice and Lactobacillus johnsonii La1 in Children.” Nutrition 24 (2008): 421-426.
Jepson, R., and J. Craig. “Cranberries for Preventing Urinary Tract Infections.” Cochrane Database of Systematic Reviews (2008): CD001321. Available through EBSCO DynaMed Systematic Literature Surveillance at http://www.ebscohost.com/dynamed.
Pham, D. Q., and A. Q. Pham. “Interaction Potential Between Cranberry Juice and Warfarin.” American Journal of Health-System Pharmacy 64 (2007): 490-494.
Shmuely, H., et al. “Effect of Cranberry Juice on Eradication of Helicobacter pylori in Patients Treated with Antibiotics and a Proton Pump Inhibitor.” Molecular Nutrition and Food Research 51 (2007): 746-751.
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