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- Cranberry (Vaccinium macrocarpon)
- Urinary Tract Infection
| Date:
08-31-2012 | HC# 081221-455
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Re: Meta-analysis Shows Cranberry Juice May Be Effective for Treatment of Urinary Tract Infection in Certain Populations
Wang CH, Fang CC,
Chen NC, et al. Cranberry-containing products for prevention of urinary tract
infections in susceptible populations: A systematic review and meta-analysis of
randomized controlled trials. Arch Intern
Med. 2012;172(13):988-996.
Urinary tract
infections (UTIs) are the most common bacterial infections, causing
approximately 7,000,000 office visits each year in the United States and
approximately 100,000 hospitalizations. Twenty to thirty percent of women who
have a UTI will have a recurrence. Cranberry (Vaccinium macrocarpon) has been a traditional remedy for UTIs for
decades. Its mechanism of action was originally thought to be acidification of
the urine, but it was later found that A-type proanthocyanidins prevented the
adhesion of the bacteria to the urinary epithelium, preventing infection. This
paper is a review and meta-analysis of the factors affecting the effectiveness
of cranberry for UTI. It goes beyond the recent Cochrane meta-analysis1
by including some new studies and providing a more thorough analysis.
The meta-analysis was
performed according to PRISMA (Preferred Reporting Items for Systematic Reviews
and Meta-analyses) guidelines. Two authors independently searched MEDLINE,
EMBASE, and the Cochrane Central Register of Controlled Trials (CENTRAL) from
inception to November 2011. Studies were not excluded because of language,
population, or year of publication; however, conference proceedings and
registered clinical trials were not included. Inclusion criteria were: (1)
randomized controlled trials (RCTs), (2) comparison of cranberry-containing
products vs. placebo or non-placebo control for prevention of UTI, and (3)
outcomes reported as incidence of UTIs.
Information gathered
from each suitable trial included: (1) type of study and study design, (2)
characteristics of the study population, (3) types of intervention and controls,
(4) definitions of UTI, (5) types of outcomes measured, and (6) number and
reasons of participants lost to follow-up. The primary outcome was incidence of
UTI.
Thirteen trials were
included, consisting of 9 parallel and 4 crossover studies; none of the latter
had washout periods. The total population was 1616 subjects. Eight trials were
conducted according to the intention-to-treat principle, and 5 trials used
per-protocol analysis. All trials but 1 were done in the free-living community.
Each study population was sub-divided into the following categories: women with
recurrent UTIs, elderly patients, patients with neuropathic bladder, pregnant
women, and children.
The forms of
cranberry used included cranberry juice (9 trials) or cranberry capsules/tablets
(4 trials). Cranberry-containing products provided by the manufacturer Ocean Spray
(Lakeville-Middleboro, Massachusetts) were
used in 6 trials. The dose ranged from 0.4 g to 194.4 g and was given for 6
months in most trials. A formulated placebo was employed in 10 trials, placebo
was not used in 2 trials, and water was used as the placebo in 1 trial. Compliance
was measured indirectly in most trials; methods included periodic interviews,
self-reported questionnaires, and pill counting of remaining study medication.
The definition of UTI
varied widely among the studies. In most trials (10), UTI was reported as a cumulative
incidence rate. These trials were used in the quantitative data synthesis
(n=1494; 794 in the cranberry group and 700 in the control group). There was
significant heterogeneity among included trials (relative risk [RR]: 0.68; 95%
confidence interval [CI]: 0.47-1.00) (I2=59%). Several analyses
showed that 1 trial was a source of heterogeneity with a large impact on the
pooled summary estimate, and so it was excluded, which improved heterogeneity.
Following this, cranberry was shown to be effective in preventing UTIs (RR:
0.62; 95% CI: 0.49-0.80) (I2=43%). It was also effective in women
with recurrent UTIs (RR: 0.53; 95% CI: 0.33-0.83) (I2=0%), female
populations (RR: 0.49; 95% CI: 0.34-0.73) (I2=34%), children (RR:
0.33; 95% CI: 0.16-0.69) (I2=0%), cranberry juice users (RR: 0.47;
95% CI: 0.30-0.72) (I2=2%), and people using cranberry-containing
products more than twice daily (RR: 0.58; 95% CI: 0.40-0.84) (I2=18%),
although the P values were not significant in meta-regression.
A funnel plot did not
show evidence of publication bias.
Results of the effectiveness
of cranberry for UTI were similar to those of the Cochrane review once the
trial with heterogeneity was excluded (when included, the results were
non-significant). The excluded study did not show effectiveness, but had the
most stringent definition of UTI (the lowest bacterial threshold) and a placebo
that included ascorbic acid, which is also known to counteract UTIs.
Sensitivity analysis
showed that there was greater effectiveness in non-controlled trials,
suggesting that an expectation of efficacy may have biased the results. Other
analyses showed that sub-populations with certain characteristics were more
likely to benefit, including those of younger age, female sex, and individuals
with recurrent UTI history. Cranberry juice was shown to be more effective than
capsules or tablets, which may be because it provides better hydration or
because there are other substances in the juice that contribute to efficacy
that may not be present in capsules or tablets. On the other hand, juice has
the drawbacks that it is high in sugar and may cause gastrointestinal or other
adverse side effects. A dosing frequency of twice a day was shown to have a
better preventive effect.
Only 1 trial
addressed dose response, and most trials did not explain their choice of
dosage. There is an ongoing study currently examining this aspect. More recent
trials (3 total) measured the concentration of proanthocyanidins in the dose
given, but it was not possible to determine an effective dose from these data.
Further studies should include declaration of the concentration of
proanthocyanidins so that their effect can be elucidated.
The authors conclude
that while the results of the meta-analysis showed that cranberry is effective
for UTIs, the results should be interpreted with great caution, because of
study heterogeneity. Cranberry may be most beneficial in a twice daily dose in
the form of juice, in women with recurrent UTIs, female populations generally, and
in children specifically. —Risa Schulman, PhD
Reference
1Jepson RG, Craig JC.
Cranberries for preventing urinary tract infections. Cochrane Database Syst Rev. 2008;(1):CD001321. doi:
10.1002/14651858.CD001321.pub4.
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