q 2000, British Geriatrics Society
Age and Ageing 2000; 29: 9–12
REVIEW
What’s the use of cranberry juice?
KEITH J. HARKINS
Elderly Services Directorate, St James’s University Hospital, Leeds LS9 7TF, UK Fax: (+44) 113 242 9195
Keywords: cranberry juice, urinary tract infections
Introduction
Urinary tract infections are common. About onequarter of women will have one at some time in their
lives, and the incidence increases with age. Those
elderly people who live in residential or nursing
homes are at particularly high risk [1, 2]. Antibiotics
are of proven benefit for the prevention and treatment of urinary infections [3, 4], but are not always
effective, and can cause side effects such as nausea,
diarrhoea and candidal infections. Whilst most asymptomatic bacteriuria in elderly people can safely be left
untreated, in some patients recurrent symptomatic
infections occur which can be distressing and potentially life-threatening.
Drinking cranberry juice is just one of the many
non-antibiotic strategies that have been advocated for
the prevention of recurrent urinary infection. These
range from simple measures such as increasing fluid
intake and double micturition to acupuncture and
oestrogen treatment of atrophic vaginitis, and are
supported by varying amounts of evidence. However,
for the purpose of this review, only the evidence for
the efficacy of cranberry juice as a therapy will be
examined. The review is based on a search of the
Medline and CINAHL databases (1966 to present), as
well as BIDS ISI (1981 to present) and the Cochrane
library [5].
The fruit
The cranberry, shown in Figure 1, is a native North
American fruit of the vaccinium genus. The juice of
the fruit is acidic and astringent, which makes it
difficult to drink at full strength. In the 1950s a more
palatable preparation was produced, which diluted
the neat juice with water and sweeteners. It is this
cranberry cocktail that is available in shops today.
Cranberry juice has been tried in several clinical
situations, including the prevention of blocked urinary
catheters [6], to deodorize offensive urine [6–8] and
to heal skin around urostomy stomas [9]. It has also
been investigated for use as an anticarcinogen [10], an
antifungal agent [11] and an antioxidant [12]. The main
claim of benefit, however, is in the prevention and
treatment of urinary tract infections.
Urinary infections
The explanation for the usefulness of cranberry juice
was thought to be the excretion of hippuric acid in
the urine (hippuric acid is a strong bacteriostatic
agent which is present in cranberries), and its potential to acidify urine. There have been several studies
examining these effects [13–17]. Unfortunately each
has studied different volumes and concentrations of
cranberry juice in small numbers of healthy subjects,
and the results have been inconsistent. However, when
the commercially available cocktail is drunk in tolerable quantities, there is little or no urinary acidification, and hippuric acid levels rarely reach bacteriostatic
concentrations [15, 17].
More recently, attention has turned to the adherence of bacteria to the epithelial cells of the urinary
tract, which is necessary if the bacteria are to cause
infection [18–23]. Escherichia coli, Proteus and
Pseudomonas are fimbriated gram-negative rods, and it
is the fimbriae that attach the bacteria to epithelial
cells. These pathogens account for most urinary tract
infections. Their fimbriae are less able to adhere to
epithelial cells in the presence of cranberry juice or
the urine of a person who has recently drunk cranberry
juice [19]. Interestingly, cranberry juice is more effective at preventing bacterial adherence than displacing bacteria already attached to epithelial cells. This
may imply that cranberry juice will be more effective as
a preventative therapy rather than a cure for people
with an established urinary infection.
Some work on E. coli suggests that cranberry
juice causes loss of fimbriae and elongation of the
bacterial cell (changes that have also been observed
after treatment with antibiotics [18]). These effects
may be due to fructose and proanthocyanidins (tannins)
which are present in cranberries [23, 24].
Whether this in vitro evidence is clinically useful
has not been answered by several clinical trials,
which have generally been of poor quality. There is
one large double-blind placebo-controlled trial [25] on
9
K. J. Harkins
drop-out rate, which casts doubt on the long-term
tolerability of cranberry juice.
In another study, 538 nursing home residents
were given either 110 ml of cranberry juice or 6 capsules containing cranberry extract. Compared with
historical controls, there was a significant reduction
in urinary tract infections from 27 per month to 20
per month [27].
There has been one study of cranberry capsules
alone. This was a double-blind crossover placebocontrolled trial. Ten subjects (women aged between
28 and 44 years) completed the 6-month study. There
were 21 urinary tract infections: 15 in the placebo arm
and six during the treatment phase (P ¼ 0.005) [28].
There are several smaller, mainly uncontrolled
trials and anecdotal reports, most of which report
favourable results [29–33]. Details of all the trials are
summarized in Table 1.
Figure 1. Cranberries and juice. q Field McNally Leathes Ltd.
153 elderly women who were volunteers from a care
home. The effect of drinking 300 ml a day of cranberry
cocktail was examined, revealing that 15% of urine
samples of those who had been drinking cranberry
juice had bacteriuria with pyuria, compared with 28%
of samples from the placebo group (P ¼ 0.004). It took
a month for the difference to become apparent. Most
patients with bacteriuria were asymptomatic. There
was a trend for less antibiotic use for treatment of
urinary infection in the cranberry group (1.7 versus 3.2
antibiotics per 100 patient months) which did not
reach statistical significance. The main criticisms of
this trial are that the control group had a higher rate
of urinary infection before the study, suggesting there
may have been sampling bias, and the main outcome
measure (asymptomatic bacteriuria) does not generally
need treating [26]. Although there was a trend towards
fewer clinically relevant urinary infections, the study
was not designed to demonstrate that effect. This
trial, in common with many of the others, had a high
Other urinary conditions
There may be a reduction in urinary odour after the
administration of cranberry juice [6–8]. All three
studies of this were uncontrolled, and two involved
few patients. In the larger study [7], which was of
220 mainly incontinent institutionalized elderly
people, the staff noticed a marked reduction in odour,
despite the atmospheric ammonia concentration
being no different after the patients had been drinking
cranberry juice. They also described fewer urinary
symptoms, such as burning on micturition. One of
the smaller trials was of 16 physically handicapped
children with urinary catheters [6]. As well as a
reduction in urinary odour, it reported a ‘dramatic’
improvement in the incidence of blocked catheters,
although there was no statistical analysis to confirm
this. The potential use of cranberry juice in adults
with indwelling catheters that are prone to blocking
is worthy of further investigation.
Table 1. The main trials of cranberries in the prevention of urinary infection
Reference
Patient group
Trial design
n
Cranberry juice
dose
Outcome
........................................................................................................................................................................................................................
Dignam et al. (1997) [27]
Elderly men and women
538
Historical
comparisons
6 capsules or
220 ml/day
Fewer UTIs
(P ¼ 0:01)
Avorn et al. (1994) [25]
Elderly women
153
Placebo-controlled
300 ml/day
Reduced bacteriuria
(P ¼ 0:004)
Haverkorn and Mandigers (1994) [30]
Elderly men and women
7
Crossover
(not blinded)
15 ml twice daily
Fewer UTIs
(P ¼ 0:004)
Walker et al. (1997) [28]
Middle-aged women
10
Crossover
(double-blind)
400 mg capsule/day
Fewer UTIs
(P < 0:005)
Foda et al. (1995) [29]
Children with neuropathic
bladders
21
Crossover
(not blinded)
15 ml/kg/day
No reduction in
prevalence of UTI
UTI, urinary tract infection.
10
Cranberry juice
In a study of 13 patients with urostomies who
drank 160–329 ml of cranberry juice a day there was
improvement in damage to the skin surrounding their
stomas [9]. This was in spite of there being no change
in urinary pH. This apparent protective effect for
the skin against urine may be relevant for patients who
are immobile and incontinent, and suffer skin damage
as a result. Again, further work is needed before
cranberry juice could be recommended for this use.
One study of patients with renal stones reported a
reduction in the urinary calcium excretion in people
after drinking cranberry juice [34] and suggested that
it may be useful in the treatment of some patients
with recurrent renal stones.
Non-urinary uses
Several other properties of cranberry juice have been
examined by in vitro studies. One report suggests that
all the fruits in the vaccinium species (cranberry,
blueberry, bilberry and lingonberry) may have anticarcinogenic properties through their effects on two
enzymes important in carcinogenesis (quinone reductase and ornithine decarboxylase). Work in this area
continues [10].
Another study examined the effect that cranberries
have on nine types of dermatophyte [11]. The growth
of eight of them was inhibited (this was a fungistatic
rather than fungicidal effect). The ninth, Candida
albicans, was unaffected. There has been no further
work in this area since the late 1960s. A single study
of the antiviral property of cranberry juice (on the
poliovirus) suggested some potential in this area [35].
The oxidation of low-density lipoprotein is an
early step in the formation of atheromatous plaques
on vascular endothelium. Cranberry juice inhibits
the in vitro oxidation of low-density lipoprotein [12].
Cranberry juice may provide benefits similar to other
dietary antioxidants, which can improve the ability
of low-density lipoprotein to resist oxidative stress in
vivo [36, 37]. This could be of benefit in the prevention
of coronary heart disease.
Finally, cranberry juice may have potential in the
prevention of dental disease by inhibiting the sticking
together of bacteria, which is necessary for them
to form dental plaques [38]. The mechanism for this
action is not known, and this is yet another possible
use for cranberries which has not been tested clinically.
Much more work needs to be done before any
clinically relevant conclusions can be drawn from any
of these studies.
Potential problems with cranberry juice
Potential problems are:
1. We do not know whether resistance or tachyphylaxis to cranberry juice develops, nor who (if
anyone) is most likely to benefit from long-term
treatment.
2. The studies cited have used different preparations
and amounts of cranberry extract, so the optimal
preparation and dose have not yet been determined.
3. Cranberry juice has a high oxalate content, and
there is a theoretical risk that a regular intake may
precipitate urinary stone formation. Urinary oxalate
excretion does not, however, rise after drinking
cranberry juice [39] and none of the studies has
reported stone formation as a problem. There are
no reported adverse effects from long-term consumption in moderate volumes.
4. At present, people have to buy the juice, which is
not available on prescription. A litre of cranberry
juice cocktail costs about £1.20 (£11 a month for
a dose of 300 ml a day).
Conclusion
There are many unanswered questions about the use
of cranberry juice. There are subjective data to justify
the popular belief that it may be useful for the prevention of urinary tract infections. However, in the
absence of well-designed controlled trials, this treatment cannot be recommended.
Rather than giving patients cranberry juice cocktail
for recurrent urinary infections when other treatments are ineffective or poorly tolerated, it would be
better to enter them in clinical trials.
Key points
• There are many unanswered questions about the
use of cranberry juice.
• Subjective data support the belief that it may be
useful for the prevention of urinary tract infections
but, in the absence of well-designed controlled
trials, the treatment cannot be recommended.
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