Cranberry-Containing Products for UTIs

It is estimated that urinary tract infections (UTIs) are the cause of 7,000,000 visits to physicians’ offices each year, along with an additional 1,000,000 emergency department visits. Community-acquired UTIs result in 100,000 hospital admissions annually and represent an estimated annual cost of $1.6 billion in the United States.

UTI is defined as the presence of clinical signs and symptoms arising from the genitourinary tract in the presence of a certain threshold level of bacteria in the urine. Adult women are particularly susceptible; 40% to 50% of women will experience at least 1 episode of UTI in their lifetimes. Of those women, approximately 20% to 30% will have a reoccurrence with concurrent short-term morbidity. Pregnant women, elderly, and those with neuropathic bladder are also at greater risk.

Patients have been using cranberry (genus Vaccinium, including the species V oxycoccus, V macrocarpon, V microcarpum, and V erythrocarpum) as a folk remedy for many years. Researchers recently conducted a study to evaluate cranberry-containing products for the prevention of UTIs and to examine the factors influencing their effectiveness. They reported study results in Archives of Internal Medicine [2012;172(3):988-996].

The researchers searched MEDLINE, EMBASE, and the Cochrane Central Register of Controlled Trials from inception to November 2011. They were looking to identify controlled trials that compared prevention of UTIs in patients who used cranberry-containing products with those who used placebo or nonplacebo controls.

There were 13 randomized controlled trials that met eligibility criteria for qualitative synthesis. The 13 included 9 parallel-group and 4 crossover trials. Eight of the trials were conducted on the intention-to-treat principle and 5 used per-protocol analysis.

The qualitative analysis included 1616 subjects. The researchers used inclusion and exclusion criteria to categorize each study population into 5 subgroups: (1) women with recurrent UTIs, (2) elderly patients, (3) patients with neuropathic bladder, (4) pregnant women, and (5) children.

There were differences in the form of administration of cranberry-containing products; 9 trials used cranberry juice and 4 used cranberry capsules or tablets. The daily cranberry dose ranged from 0.4 g to 194.4 g (3 trials reported daily use of cranberry-containing products without specifying the actual cranberry amount). In most of the trials, the cranberry-containing products were administered for 6 months.

A total of 1494 subjects were further analyzed in a quantitative synthesis with 794 in the cranberry group and 700 in the control group. There was significant heterogeneity among the trials (risk ratio [RR], 0.68; 95% confidence interval [CI], 0.47-1.00). After excluding the trial that had the most significant impact on the polled summary estimate, heterogeneity decreased. The random-effects pooled RR for cranberry users versus nonusers was 0.62 (95% CI, 0.49-0.80).

On subgroup analysis, cranberry-containing products seemed to be more effective in women with recurrent UTIs (RR, 0.53; 95% CI, 0.33-0.83), female populations (RR, 0.49; 95% CI, 0.34-0.73), children (RR, 0.33; 95% CI, 0.16-0.69), cranberry juice users (RR, 0.47; 95% CI, 0.30-0.72), and people using cranberry-containing products more than twice daily (RR, 0.58; 95% CI, 0.40-0.84), although, the researchers noted, the P values were not significant in meta-regression.

In summary, the researchers said, “Our findings indicate that cranberry-containing products are associated with protective effect against UTIs. However, this result should be interpreted in the context of substantial heterogeneity across trials.”