Many
women drink cranberry juice hoping to prevent cystitis
“It’s a myth that
cranberry juice can cure bladder infections,” the Daily Mail reported today.
The story was based on a large review of research that looked at the
effectiveness of cranberry juice and cranberry products such as capsules, in
preventing bladder and other urinary tract infections (UTIs), which are most common
in women.
The
use of cranberry juice to protect against infection was first thought to have
originated with Native Americans. It is now a popular home remedy, often
recommended to women by their doctors to help prevent infections on the basis
of previous research that suggested it could be helpful. The theory is that
cranberry juice contains substances that help prevent bacteria from sticking to
the wall of the urinary tract. However, this new widely reported study found
that overall, cranberry products did not reduce the occurrence of UTIs, such as
cystitis, when compared with placebo, water or no treatment at all.
This
updated review comes from the respected Cochrane Collaboration and its results
are likely to be reliable. It suggests that while cranberry juice may be of
small benefit to some women, it would need to be consumed in such large
quantities as to make it unacceptable to many as a remedy. Other cranberry
products were also found to be ineffective, possibly due to the lack of potency
of the active ingredients. Other methods women can use to reduce the risk of
developing a UTI include drinking plenty of fluids and practising good hygiene.
What
to do if you think you have a UTI
Although
cranberry juice is sometimes recommended by doctors as a way of preventing
bladder and other urinary tract infections, it has never been advised as a
treatment. If you think you have
symptoms of a UTI, such as a frequent need to urinate or pain when passing
urine, you should see your GP. You may need treatment with antibiotics.
Where
did the story come from?
The
study was carried out by researchers from the Cochrane Collaboration, an
independent international organisation that publishes regular systematic
reviews on the effectiveness of healthcare interventions. There was no external
funding. The study was published in the peer-reviewed latest edition of the
Cochrane Library, which is available to everyone. Generally,
the media covered the study fairly. Several papers used the term “cystitis” as shorthand
for bladder and other urinary tract infections. Cystitis is a painful
inflammation of the bladder that can cause an urgent need to urinate and pain
on urinating. It is often, but not always, caused by a bacterial infection.
Infection may also affect other parts of the urinary tract including the
urethra, kidneys and ureter, when it is more serious.
What
kind of research was this?
This
was a systematic review to assess the effectiveness of cranberry products in
preventing urinary tract infections in susceptible people, including:
•women
with recurrent UTIs
•children
•people
with certain bladder problems, such as kidney stones that make them more vulnerable
to infection
•older
people
UTIs
are very common, more so in women than in men, possibly because women have a
shorter urethra that may allow bacteria to get into the bladder more easily. It
is estimated that half of all women in the UK will have a UTI at least once in
their life. Some women seem to be particularly susceptible, with an average of
two or three infections annually. Antibiotics are often advised as a
preventative measure in people at risk of recurrent UTIs. Children can also get
UTIs, though less commonly, and elderly people are also vulnerable. Other
at-risk groups are patients with spinal cord injuries and/or catheters, and
those with certain chronic diseases such as diabetes or HIV.
The
researchers point out that cranberries have been widely used for several
decades to prevent and treat UTIs. Research suggests that they contain two
constituents that may prevent bacteria (particularly E. coli, thought to be the
bacterium that commonly causes bladder infections) from sticking to the bladder
lining. The two substances are fructose and proanthocyanidins (PACs).
Cranberry
products include juice, syrup, capsules and tablets. A commonly recommended
amount for UTI prevention is 300ml of a cranberry juice “cocktail” containing
36mg of PACs. However, the researchers point out that the processing involved
in making cranberry products such as tablets and capsules may result in little
PACs being left in the final product.
What
did the research involve?
Researchers
set out to test whether cranberry juice and other products were more effective
than either placebo or no treatment, or any other treatment in the prevention
of UTIs in susceptible populations. They also wished to test whether different
cranberry products differed in how well they prevented UTIs. They searched a
number of electronic databases for all randomised controlled trial (RCT) and
quasi-RCTs (RCT-type studies that did not meet the expected standard due to
flaws or limitations into how the study was conducted, such as not being
properly blinded) on the effectiveness of cranberry products in the prevention
of UTIs. They also contacted companies
involved in the promotion and distribution of cranberry products for
information on both published and unpublished studies, and searched reference
lists of review articles and relevant studies. They also searched by hand a number of
specialist journals and the proceedings of major relevant conferences.
Non-English language studies were included.
The
studies included were of the following groups:
•those
with a history of recurrent UTI (more than two episodes in the previous 12
months)
•elderly
people
•people
needing catheterisation (a risk factor for UTI), either permanently or
intermittently
•pregnant
women
•people
with abnormalities of the urinary tract
•children
with a UTI
They
excluded any studies in which cranberry products were tested as a treatment for
UTI, and studies of any urinary tract condition not caused by a bacterial
infection. Participants in the trials took cranberry products for at least one
month. The authors looked primarily at whether cranberry products affected the
number of UTIs experienced, as confirmed by laboratory analysis of urine
specimens. They also looked at how far participants in the trials stuck to
therapy, and potential side effects.
Two
of the authors independently assessed the quality of all the studies eligible,
using a validated tool to assess the risk of bias, and extracted the relevant
data on study methods, participants, interventions and outcomes. Using standard
statistical methods they performed a meta analysis to calculate a summary
measure for how well cranberry products prevent recurrent UTIs.
What
were the basic results?
The
review includes 24 studies with a total of 4,473 participants, comparing
cranberry products with control or alternative treatments. Ten of the studies
had been included in a previous review carried out by the researchers in 2009
into the same question. Studies included seven of women with recurrent UTIs,
four of elderly men and women, three of patients needing catheterisation, two
of pregnant women and three of children at risk. The main findings are below:
•Compared
with placebo, water or no treatment, cranberry products did not significantly
reduce the occurrence of UTI overall (relative risk (RR) 0.86, 95% confidence
interval (CI) 0.71 to 1.04)
•Nor
did cranberry products reduce UTIs in any of the individual subgroups: women
with recurrent UTIs (RR 0.74, 95% CI 0.42 to 1.31); older people (RR 0.75, 95%
CI 0.39 to 1.44); pregnant women (RR 1.04, 95% CI 0.97 to 1.17); children with
recurrent UTI (RR 0.48, 95% CI 0.19 to 1.22); cancer patients (RR 1.15 95% CI
0.75 to 1.77); people with bladder abnormalities or spinal injury (RR 0.95, 95%
CI 0.75 to 1.20).
•Overall
heterogeneity – that is, the differences in results between trials – was
moderate (I² = 55%).
•The
effectiveness of cranberry was not significantly different to antibiotics for
women (RR 1.31, 95% CI 0.85, 2.02) and children (RR 0.69 95% CI 0.32 to 1.51).
•Cranberry
products were not associated with any adverse effects compared with placebo/no
treatment (RR 0.83, 95% CI 0.31 to 2.27).
•Many
studies reported low compliance and high withdrawal/dropout problems, which
they attributed to palatability/acceptability of the products, primarily the
cranberry juice.
•Most
studies of other cranberry products (tablets and capsules) did not report how
much of the “'active” ingredient the product contained, and therefore the products
may not have had enough potency to be effective.
How
did the researchers interpret the results?
The
researchers say that the new review shows that cranberry juice does not appear
to have a significant benefit in preventing urinary tract infections. Although
some of the smaller studies demonstrated a small benefit for women with
recurrent UTIs, there were no statistically significant differences when the
results of a much larger study were included.
They
also argue that low compliance and high dropout rates in the studies show that
drinking the juice may be unacceptable in the long term. Cranberry products
were also ineffective (although they had the same effect as taking antibiotics
preventatively), possibly due to lack of potency of the potential “active
ingredient”. From the evidence they conclude it is unlikely that cranberry in
its juice form is going to be an acceptable and effective intervention. Even if
its “anti-adhesion” qualities could be proven, they calculate that to maintain
levels of the PACs thought necessary to prevent bacteria sticking to the
bladder lining, people would have to drink 150ml of the juice twice a day for
an indefinite length of time. “If a woman only has two UTIs a year she would
have to drink the juice twice a day for a year to potentially have one less
UTI. Although for some women this regime may be acceptable (i.e. those who have
a high rate of occurrence), others may find that the price, the calories in the
juice, and the taste may make it less appealing”. They argue that other
preparations need to be quantified using standardised methods to ensure they
contain enough of the potential 'active' ingredient, before being evaluated in
clinical studies or recommended for use.
These
findings conflict with those that the researchers presented in their earlier
2009 review. But revising or rejecting theories when new evidence becomes
available (as opposed to trying to make the evidence "fit" with
pre-existing theories) is in the best tradition of evidence-based medicine.
Conclusion
This
updated review comes from the well-respected Cochrane Collaboration and its
results are likely to be reliable. As the authors point out, although their
previous review of 11 studies found some evidence that cranberry juice may reduce
UTIs, the addition of 14 new studies suggest cranberry juice is less effective
than previously indicated.
Some
people find pure cranberry juice a bit sour, so if you only drank it for your
health and not for the taste, it may be time to switch to a tastier
alternative. If you do enjoy drinking cranberry juice, then it may be a good
way to get your 5 a Day (although you should be aware that many cranberry
‘juice drinks’ contain a lot of sugar to reduce the sourness). At the moment it
seems doubtful that there is any way of knowing if other cranberry products
contain enough of the potential “active ingredient” to be properly evaluated.
NHS UK
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