Cranberry juice 'useful' for women with recurring UTIs, claims study

“Drinking cranberry juice could reduce the worldwide use of antibiotics,” is the somewhat optimistic headline in The Daily Telegraph.

A new study found some modest preventative benefit in women with a history of reoccurring urinary tract infections (UTIs), though this arguably doesn’t amount to an effective weapon in the war against antibiotic resistance.

In the interests of transparency, it is important to point out that the study was funded by Ocean Spray Cranberries and two of the authors were employed by the company.

This was a six-week trial in 373 healthy women who drank either a 240ml bottle of cranberry juice or identical-tasting placebo every day for six weeks. It found that cranberry juice reduced the number of symptoms associated with UTIs.

The scale of the preventative effective was modest. The researchers estimated that, on average, for every woman who drank cranberry juice for 3.2 years, just one UTI would be prevented. That’s a lot of cranberry juice.

The study had a good sample size, duration of follow-up, regular assessments, and participants and researchers were unaware of the study group. However, it’s important to realise that the juice only seemed to reduce the number of infections across the group – not treat them. Women with an actual infection still needed to take antibiotics. The study also excluded people who may be most susceptible to urine infections.

The decision whether to drink daily cranberry juice remains a personal one – but it is worth bearing in mind that these drinks are usually high in sugar.  

Where did the story come from?

The study was published in the peer-reviewed American Journal of Clinical Nutrition. Funding was provided by Ocean Spray Cranberries Inc. which provided the drink used in the study. Two of the study authors work for the firm.

While industry funding for a study is not unusual, actually having authors of a study being employed by a funding company is. While there is no suggestion of obvious bias, the study is vulnerable to accusations of a conflict of interests, due to an unconscious bias on the part of the company’s employees.

The study was published on an open access basis, so you can read it for free online.

The Telegraph and The Daily Mail acknowledge the potential conflict of interest inherent in the study, but also suggest that cranberry juice could help combat antibiotic resistance at face value. This seems quite a bold claim, given the modest effects reported in the study.

The Metro takes a more critical approach, citing a number of objections raised by the American news website, Vox, which attacks the methodology of the study.

What kind of research was this?

This was a randomised controlled trial aiming to looking at the effects of drinking cranberry juice on episodes of UTIs in women.

UTIs are common among healthy women, and it is estimated that between a quarter and a third of women who develop an infection will have a recurrent one within the following six months.

Antibiotics are used in the treatment and prevention of UTIs. However, the increasing problem of antibiotic resistance and the side effects of antibiotics make this far from ideal.

Cranberries have often been proposed to have benefits in protecting against UTIs (a claim thought to date back to Native American tradition).

A double-blind placebo-controlled trial such as this is the best way of investigating this theory. 

What did the research involve?

The trial was carried out across 18 clinics in the US and involved 373 healthy women (average age 41) who had suffered two or more UTIs over the past year. Women with a current UTI and those taking preventative antibiotics were excluded.

They were randomised to drink a 240ml bottle of cranberry juice or identical placebo (a flavoured, sugary drink) every day for six months.

Participants kept a daily diary to record any UTI symptoms. They attended planned clinic assessments at two, four and six months, but if they experienced UTI symptoms at any time they contacted the research centre to attend for another assessment.

At assessments, urine samples were collected and tested. The main outcome of interest was the frequency of UTI symptoms. Other outcomes included the incidence of UTI with positive urine test, and side effects.

Throughout the study, participants were asked to avoid cranberries and blueberries or their products, and probiotics, including yoghurt. Compliance was assessed by asking participants to return all used and unused bottles at the end of the study – and was 98%. 322 of the randomised participants (86%) completed the full six-month study.

What were the basic results?

Cranberry juice significantly reduced the incidence of UTIs. During follow-up, there were 39 symptomatic infections in the cranberry group compared with 67 in the placebo group, with an annual incidence of 0.48 vs. 0.75. This meant that cranberry juice reduced the incidence of UTIs by over a third (rate ratio 0.61, 95% confidence interval [CI] 0.41 to 0.91).

With confirmation by urine dipstick, there were 32 infections vs. 53. Adjusting for antibiotic use during UTIs did not significantly affect the results.

Overall, the researchers estimated that cranberry juice would prevent roughly one symptomatic UTI per three women per year (“One clinical UTI event was prevented for every 3.2 woman years”).

The only difference in side effects between groups was at two months, when nausea was reportedly more common in the placebo group (5.9% vs. 1.6% of participants in the cranberry group).

How did the researchers interpret the results?

The researchers conclude: “The consumption of a cranberry juice beverage lowered the number of clinical UTI episodes in women with a recent history of UTI”.

Conclusion

This trial found that drinking cranberry juice daily for six months reduced the number of symptomatic urine infections among healthy women, compared with placebo.

The study had a good sample size, reasonably long testing period, was double-blind, including reportedly identical tasting-and-smelling placebo. It also carried out thorough assessments, verifying any reported symptoms with urine tests.

However, there are a few points to note.

• The study found that cranberry juice seemed to prevent the incidence of urine infection symptoms. It does not show that if you have an actual urine infection you are better off just drinking cranberry juice, as it is better or just as good at clearing the infection as antibiotics. Women who developed an infection in this study were still given antibiotic treatment.
• The study excluded women who needed to take preventative antibiotics and others who may be at a higher risk of UTIs, such as those with indwelling catheters, any problems or abnormalities of the urinary tract, those with sensory problems (e.g. spinal injuries), and those over 70 (thereby excluding many infirm people, care home residents, etc.).
• Therefore, this study provides no evidence that cranberry juice is effective in higher-risk women. Neither does the study look at the effects in men, or children and young people aged under 20. 
• Cranberry juice is a very high-sugar drink that also contains a lot of additives. In fact, this study used a less additive-laden version with a shorter shelf life that is not commercially available. Therefore, people may need to individually consider whether the potential benefits of daily consumption of a high-sugar drink in the long term are worth it.
• As the researchers acknowledge, effects may be different with consumption of cranberries in a different form, such as in powders or capsules, or the berry itself.

The researchers say their findings, “suggest that the consumption of cranberry is a useful strategy for reducing recurrent clinical UTI episodes and antibiotic use”. However, the decision to try cranberry juice or not will need to remain an individual one.

It is estimated that half of all women will get a UTI at least once in their life, so the occasional infection is not usually a cause for concern. If you find yourself having repeated UTIs or persistent symptoms such as pain or irritation, or blood in your urine, then contact your GP. There may be underlying issues that need further investigation.

Links To The Headlines

Cranberry juice can reduce need for antibiotics by combating UTIs, research finds. The Daily Telegraph, June 20 2016

How cranberry juice can stave off infections: Compound in the fruit could reduce need for antibiotics because it prevents bacteria from sticking. Daily Mail, June 20 2016

Turns out cranberry juice might not do anything to help with UTIs. Metro, June 18 2016

Links To Science

Maki KC, Kaspar KL, Khoo C, et al. Consumption of a cranberry juice beverage lowered the number of clinical urinary tract infection episodes in women with a recent history of urinary tract infection. American Journal of Clinical Nutrition. Published online June 2016