Is Cranberry Juice (or pills) Good for Urinary Tract Infections?

What is Cranberry?

Urinary tract infections (UTI) are among the most common health problems, affecting millions worldwide yearly. Although UTIs are treatable with antibiotics, the excessive use of these drugs can lead to the development of bacterial resistance, which has become a growing concern in the health field. Consequently, finding viable alternatives to prevent these infections has recently gained significant importance.

One fruit that has been widely studied for its protective potential is the cranberry.

Cranberries are a group of dwarf shrubs or vines of the subgenus Oxycoccus of the genus Vaccinium. Their scientific names include: Vaccinium oxycoccos, Vaccinium macrocarpon or Oxycoccus macrocarpus.

What are Cranberries Good for?

Cranberries are small red fruits rich in antioxidant and anti-inflammatory compounds. Traditionally, Native Americans have used the fruit or its leaves to treat various ailments, including bladder, stomach, and liver disorders, as well as diabetes, wounds, and other health conditions. However, no clear scientific evidence exists that cranberry is effective against most of these conditions.

Because they are rich in vitamin C (100 grams of fresh cranberries contain about 13.3 mg of vitamin C), cranberries were widely used in Europe to combat scurvy, a disease caused by prolonged vitamin C deficiency.

Cranberries can be consumed in a variety of ways. In cooking, it is usually used as juice, sauce, jam, or in desserts. As a dietary supplement, they are available as liquid concentrate, capsules, tablets, or powdered extracts.

Cranberry for UTI

In the 1980s, studies on cranberry identified a substance called proanthocyanidin type A, which, besides being a potent antioxidant, also appears to have the capability to prevent bacteria such as Escherichia coli, the primary cause of UTIs, from adhering to the urinary tract walls. This “anti-adherence” mechanism may inhibit bacteria from establishing, multiplying, and causing infections.

Since then, interest in cranberry’s potential properties in treating or preventing urinary tract infections has significantly increased (in the form of cranberry juice, tablets, or capsules). However, contradictory results published by various studies have made it difficult to draw a conclusion.

What Do Scientific Studies Show?

Until the early 2000s, there were no controlled clinical trials evaluating the efficacy of cranberry in urinary tract infections. Until then, the level of evidence was weak, and the low quality of the studies did not allow any conclusions to be drawn.

Over the past two decades, however, the number of studies on cranberry has increased dramatically. Despite conflicting results, the greater number of high-quality clinical trials now gives us a better idea of its effectiveness.

The Cochrane Database of Systematic Reviews has been publishing meta-analyses on the role of cranberries in urinary tract infections since 1998, with updates in 2003, 2004, 2008, 2012, and most recently in April 2023.

This Cochrane systematic review is currently the most relevant study on cranberries. The 2023 publication included 50 controlled clinical trials involving a total of 8857 people. The conclusions were as follows:

• Cranberry consumption in the form of juice, tablets, or capsules reduced the number of UTIs in women with recurrent UTIs (26% reduction), children (54% reduction), and patients undergoing urinary tract procedures, such as bladder radiotherapy (53% reduction).
• On the other hand, UTIs did not appear to be reduced in elderly individuals in long-term care facilities (men and women), adults with neuromuscular bladder dysfunction and incomplete emptying, or pregnant women.
• There wasn’t enough information to determine whether cranberry products are more or less effective compared to antibiotics in preventing new UTIs.
• The effectiveness in preventing urinary tract infections appears restricted to cases caused by Escherichia coli.
• Cranberry in the form of juice, tablets, or capsules seems to be equally effective.
• Studies only suggest some benefit in preventing urinary tract infections, with no evidence of cranberry’s efficacy in treating UTIs.

Recommended Doses

One of the major issues with using cranberries for urinary tract infection prevention is the lack of an established regimen for dosage and treatment duration, nor is there formal regulation by health authorities for cranberry products. Some manufacturers don’t even indicate a suggested dose on the package.

Typically, we suggest a glass of cranberry juice (approximately 240 mL or eight oz.) once or twice a day, or cranberry concentrate tablets with a total daily dose of 500 mg to 1000 mg. However, there is no data proving this dosage to be the most effective. For children, we recommend cranberry juice at 5 mL/kg per day, with a maximum of one glass per day.

Cranberry juice should be consumed in its pure, unsweetened form to avoid excessive sugar intake (the fruit naturally contains sugar), which could be counterproductive for overall health and the balance of urinary flora. This suggestion, however, can be particularly problematic for children, given that cranberries have a naturally bitter and acidic taste, which is mitigated when sweetened.

Side Effects

The adverse effects of cranberry products are minimal. This is often the main argument for their use, despite evidence of their effectiveness still inconclusive. Generally, they do not harm and may even have some beneficial effects.

The most common drawbacks are the additional calories and glucose intake and gastrointestinal side effects such as heartburn, nausea, and diarrhea, especially at high doses.

High doses may also increase the risk of oxalate-based kidney stones in predisposed individuals.

Contraindications and Precautions

There are no absolute contraindications to the use of cranberries, except for a history of allergy to cranberries or other red fruits.

In diabetic patients, capsules or tablets are preferable to avoid the excess calories and sugar found in juice.

Individuals on anticoagulants, such as Warfarin, should use cranberry with caution, as there is a theoretical potential for drug interaction, although current evidence is inconclusive.

Cranberries may slow down the rate at which the body metabolizes atorvastatin, nifedipine, and Diclofenac, potentially intensifying both their desired effects and side effects. Limiting the consumption of large quantities of cranberry juice while on those medications is advisable.

The use of cranberry in people with chronic kidney disease should be approached with caution. Cranberries contain a significant amount of oxalate, a compound that can contribute to the formation of kidney stones, especially in individuals with a predisposition or existing kidney disease.

Little is known about the safety of cranberry during pregnancy or lactation. As current evidence suggests a lack of efficacy in pregnant women, the risk-benefit ratio does not support its use in pregnant women.

In light of current scientific knowledge, cranberry appears to be effective and safe in reducing the incidence of urinary tract infection in women with recurrent cystitis, children, and patients undergoing urinary tract surgery. However, this efficacy does not extend to institutionalized elderly, pregnant women, or individuals with neurogenic bladder. There is no evidence of effectiveness in the treatment of urinary tract infections.

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References

• A systematic review of the evidence for cranberries and blueberries in UTI prevention – Molecular nutrition and food research.
• Cranberries for preventing urinary tract infections – Cochrane.
• Cranberry-containing products for prevention of urinary tract infections in susceptible populations: a systematic review and meta-analysis of randomized controlled trials – JAMA.
• Can Cranberries Contribute to Reduce the Incidence of Urinary Tract Infections? A Systematic Review with Meta-Analysis and Trial Sequential Analysis of Clinical Trials – The Journal of urology.
• Cranberry – NIH – National Center For Complementary and Alternative Medicine.
• Recurrent simple cystitis in women – UpToDate.
• Urinary tract infections in children: Long-term management and prevention – UpToDate.
• Images: Depositphotos.

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