Cranberries as a dietary supplement
Cranberries are often marketed as a dietary supplement primarily for their potential health benefits, particularly in preventing bladder infections. Historically, Native Americans utilized cranberries both as a food source and for medicinal purposes, and this knowledge influenced early European settlers. Modern scientific inquiries have shifted focus, and current research suggests that cranberries may work by preventing certain bacteria from adhering to the bladder wall, which could help reduce urinary tract infections (UTIs).
Cranberries have also been explored for other health applications, including potential roles in cancer prevention, heart disease management, and improving oral health. However, evidence supporting these uses remains limited or mixed. While cranberries are generally considered safe for most people, they may interact with certain medications, particularly blood thinners like warfarin, and could pose risks for individuals with specific health conditions. Dosage recommendations vary, with cranberry juice typically suggested at eight to sixteen ounces daily. Despite the promising aspects of cranberries as a supplement, ongoing research is necessary to better understand their efficacy and safety in various health contexts.
Cranberries as a dietary supplement
- PRINCIPAL PROPOSED USE: Bladder infection
- OTHER PROPOSED USES: Cancer prevention, heart disease prevention, periodontal disease prevention and treatment, ulcer prevention and treatment
DEFINITION: Natural food promoted as a dietary supplement for specific health benefits
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 small bladder stones referred to as “bladder gravel," and to remove “blood toxins.”
In the 1920s, researchers observed that drinking cranberry juice made 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, cranberry acidification of the urine is unlikely to play an important role in the treatment of bladder infections. Modern studies have 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 the adhesion of bacteria to the bladder, preliminary evidence suggests that it might also help prevent the 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, the sweeteners added to cranberry juice harm teeth, but without sweeteners, cranberry juice is very bitter.
Cranberry has been shown in several studies to have very high levels of phenols, antioxidants, anti-cancer, and anti-inflammatory properties. Because of this, it has 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 helpful for these conditions. However, a study published in 2021 in Nutrients found that cranberry lowered systolic blood pressure, especially in patients over fifty. Another study failed to find cranberry significantly effective in enhancing mental function. Research remains mixed concerning cranberry supplementation and its effectiveness in treating human disease.
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, though cranbetter tablets were more cost effective.
A double-blind study of 376 hospitalized older adults attempted to determine whether a low dose of cranberry juice would help prevent acute infections. The study tested ten ounces of cranberry juice cocktail daily—a very low dose compared to the previous study. The study failed to find benefit, perhaps partly because of the dosage of cranberry and the low number of infections that developed overall.
Another double-blind study evaluated cranberry juice cocktail to treat chronic bladder infections. This trial followed 153 women with an average age of 78.5 years over a period of six months. Many women of this age group have chronic asymptomatic bladder infectionssigns of bacteria in the urine without any symptoms. One-half of the participants were given ten ounces a day of a standard commercial cranberry cocktail drink, and the other was 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 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.
However, three other double-blind, placebo-controlled studies evaluated the effectiveness of cranberry extract in 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. pyloribut 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 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 therapyomeprazole, amoxicillin, and clarithromycin, known as OACsed 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.
Some research indicates cranberries and cranberry products and supplements may be beneficial in improving specific types of aerobic performance in athletes. However, this research is preliminary and requires further study.
In 2020, the US Food and Drug Administration announced that cranberry supplements and food products could begin using a label on their products, stating that limited evidence supports the daily use of cranberry to reduce UTIs in healthy women. While manufacturers must use the words “limited” and “inconsistent,” the permission of such a label is rare in health food products. Does this mean that women undergoing ulcer treatment may benefit from cranberry? Perhaps, but not necessarily. When a treatment fails to produce benefit for the entire group studied, researchers may, after the fact, look for a subgroup that did benefit. The laws of chance alone ensure that they can almost always find one. Therefore, whether cranberry is beneficial or positive findings were merely a statistical fluke is unclear.
Dosage
The usual dosage of cranberry extract is between 120 and 1600 milligrams (mg) twice daily for up to twelve weeks. The usual dosage of pure cranberry juice, not cranberry juice cocktail, is eight to sixteen ounces daily. Dried cranberry powder is usually taken by mount for up to six months at between 250 and 1,500 mg 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 eight 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
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Gotteland, M., et al. “Modulation of Helicobacter pylori Colonization with Cranberry Juice and Lactobacillus johnsonii La1 in Children.” Nutrition, vol. 24, 2008, pp. 421-26.
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Nelson, Angela, et al. "Cranberries: Nutritional Benefits." WebMD, 5 Jan 2024, www.webmd.com/food-recipes/health-benefits-cranberries. Accesse 1 Oct. 2024.
Parenteau, Francis, et al. “Cranberry Supplementation Improves Physiological Markers of Performance in Trained Runners.” Physical Activity and Nutrition, vol. 27, no. 4, 2023, pp. 8-14. doi:10.20463/pan.2023.0032.
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Richter, Chesney, K. "Effects of Cranberry Juice Supplementation on Cardiovascular Disease Risk Factors in Adults with Elevated Blood Pressure: A Randomized Controlled Trial." Nutrients, vol. 13, no.8, 2021. doi:10.3390%2Fnu13082618.
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, vol. 51, 2007, pp. 746-51.