Cranberry

What it is

Cranberry is the fruit of a low evergreen shrub that grows in wet ground in the north-eastern and north-central parts of North America. The berries have a long history of use as food, dye and traditional medicine, and today the fruit, its juice and dried extracts in tablets and capsules are sold mainly for urinary tract infections. The constituents usually credited with the urinary effect are proanthocyanidins (PACs), which are thought to stop bacteria sticking to the bladder wall. Laboratory analysis of marketed cranberry supplements has found that the amount of PAC declared on the label, and even the presence of cranberry material at all, frequently does not match what is in the capsule.

What the research says

The best evidence is a 2023 Cochrane review of 50 randomised trials. It found moderate-certainty evidence that cranberry products reduce symptomatic, culture-verified urinary tract infections in three specific groups - women with recurrent UTIs, children, and people made susceptible to UTI by a medical intervention - and low-certainty evidence of little or no benefit in elderly people in institutions, in pregnant women, and in adults with incomplete bladder emptying. Against antibiotics, cranberry made little or no difference. The FDA, reviewing the same field in 2020, concluded the evidence did not reach the standard for an authorised health claim and permitted only a 'limited' or 'limited and inconsistent' qualified claim. Cranberry is a prevention question, not a treatment: nothing here shows it clears an infection you already have. Gastrointestinal upset is the common side effect, a randomised crossover study showed it increases the anticoagulant effect of warfarin, and product quality is demonstrably erratic.

Evidence grade: Disputed.

What goes wrong

Cochrane rated it moderate-certainty evidence that gastrointestinal side effects probably do not differ with cranberry products, but the pooled estimate was a 33% higher relative risk whose confidence interval only just reached no difference. (Source 1)

• Systematic review, Moderate certainty.
• Size: 2,166 participants across 10 trials.
• Who: participants in placebo or no-treatment controlled cranberry trials.
• How long: not stated in the abstract.
• Result: RR 1.33, 95% CI 1.00 to 1.77; I2 = 0%.
• Funding: not stated in the abstract.

Limit of this finding: The review's phrase "probably does not differ" sits on a result whose central estimate is a 33% higher risk of gastrointestinal side effects (RR 1.33), with a 95% confidence interval running from 1.00 to 1.77. The lower end only just touches no difference, so the data are also compatible with roughly three-quarters more stomach and bowel side effects on cranberry. Read the sentence as "not shown to differ", not as evidence that cranberry causes no more gut upset than placebo.

The number of participants with gastrointestinal side effects probably does not differ between those taking cranberry products and those receiving placebo or no specific treatment(10 studies, 2166 participants: RR 1.33, 95% CI 1.00 to 1.77; I2 = 0%; moderate certainty evidence).

In a randomised crossover study in healthy men, two weeks of cranberry increased the anticoagulant effect of a single warfarin dose without changing warfarin blood levels. (Source 2)

• Blood level study, Low certainty.
• Size: 12 healthy male subjects.
• Who: healthy men of known CYP2C9 and VKORC1 genotype.
• How long: 2 weeks of pretreatment before a single 25 mg warfarin dose.
• Result: area under the INR-time curve increased by 30% versus warfarin alone; no change in S- or R-warfarin pharmacokinetics or plasma protein binding.
• Funding: not stated in the abstract.

Cranberry significantly increased the area under the INR–time curve by 30% when administered with warfarin compared with treatment with warfarin alone.

Laboratory analysis of 24 European cranberry supplements found most failed the pharmacopoeia uniformity test, most mis-stated their PAC content, and only five actually contained cranberry. (Source 3)

• Survey study, Certainty not rated.
• Size: 24 dietary supplement products.
• Who: cranberry-labelled dietary supplements on the European market.
• How long: single laboratory analysis.
• Result: 17 of 24 products failed the uniformity of dosage forms test; 16 of 24 declared an incorrect amount of PACs; 5 of 24 contained cranberry on chemical fingerprinting.
• Funding: not stated in the abstract.

Our results showed that 17 DS did not comply with the uniformity test of dosage forms, and only five contained cranberry. Finally, 16 DS claimed an incorrect amount of PACs.

POSITION: NCCIH (page updated November 2024) says oral cranberry is generally thought to be safe but that very large amounts can cause stomach upset and diarrhoea, especially in young children. (Source 4)

• Official position, Certainty not rated.
• Size: not applicable.
• Who: general population, with young children singled out.
• How long: not applicable.
• Result: no rates given on the page.
• Funding: US government agency page.

Cranberry taken orally (by mouth) is generally thought to be safe. However, if consumed in very large amounts, cranberry can cause stomach upset and diarrhea, particularly in young children.

POSITION: NCCIH describes the evidence on cranberry and warfarin as conflicting. (Source 4)

• Official position, Certainty not rated.
• Size: not applicable.
• Who: people taking warfarin.
• How long: not applicable.
• Result: no numbers given on the page.
• Funding: US government agency page.

There is conflicting evidence about whether cranberry interacts with the anticoagulant (blood thinner) warfarin.

What the evidence supports

In the 2023 Cochrane review, cranberry products probably reduced symptomatic, culture-verified UTIs in women with recurrent UTIs. (Source 5)

• Systematic review, Moderate certainty.
• Size: 1,555 participants across 8 trials, within a review of 50 studies and 8,857 randomised participants.
• Who: women with recurrent urinary tract infections.
• How long: not stated in the abstract; trials varied.
• Result: RR 0.74, 95% CI 0.55 to 0.99; I2 = 54%.
• Funding: not stated in the abstract.

cranberry products probably reduced the risk of symptomatic, culture-verified UTIs in women with recurrent UTIs (8 studies, 1555 participants: RR 0.74, 95% CI 0.55 to 0.99; I2 = 54%)

The same review found a reduction in symptomatic, culture-verified UTIs in children, with low statistical heterogeneity. (Source 5)

• Systematic review, Moderate certainty.
• Size: 504 participants across 5 trials.
• Who: children.
• How long: not stated in the abstract.
• Result: RR 0.46, 95% CI 0.32 to 0.68; I2 = 21%.
• Funding: not stated in the abstract.

in children (5 studies, 504 participants: RR 0.46, 95% CI 0.32 to 0.68; I2 = 21%)

What the evidence does not support

In the same review there may be little or no benefit in elderly institutionalised men and women, or in pregnant women, and the authors rated this evidence low certainty. (Source 5)

• Systematic review, Low certainty.
• Size: 1,489 participants across 3 trials (elderly); 765 participants across 3 trials (pregnancy)
• Who: elderly people in institutions; pregnant women.
• How long: not stated in the abstract.
• Result: elderly RR 0.93, 95% CI 0.67 to 1.30; I2 = 9%. Pregnant women RR 1.06, 95% CI 0.75 to 1.50; I2 = 3%.
• Funding: not stated in the abstract.

However, in low certainty evidence, there may be little or no benefit in elderly institutionalised men and women (3 studies, 1489 participants: RR 0.93, 95% CI 0.67 to 1.30; I2 = 9%), pregnant women (3 studies, 765 participants: RR 1.06, 95% CI 0.75 to 1.50; I2 = 3%)

The Cochrane authors state plainly that the available evidence does not support cranberry use in three named populations. (Source 6)

• Systematic review, Low certainty.
• Size: 50 studies, 8,857 participants.
• Who: elderly people, patients with bladder emptying problems, pregnant women.
• How long: not stated.
• Result: no quantitative estimate given in the conclusion; the subgroup estimates all crossed 1.0.
• Funding: not stated in the abstract.

The evidence currently available does not support its use in the elderly, patients with bladder emptying problems, or pregnant women.

Head to head with antibiotics, cranberry products may make little or no difference to culture-verified UTIs. (Source 7)

• Systematic review, Low certainty.
• Size: 385 participants across 2 trials (culture-verified); 336 participants across 2 trials (symptoms without culture)
• Who: participants in trials comparing cranberry with antibiotic prophylaxis.
• How long: not stated in the abstract.
• Result: RR 1.03, 95% CI 0.80 to 1.33; I2 = 0% for culture-verified UTI; RR 1.30, 95% CI 0.79 to 2.14; I2 = 68% for clinical symptoms without culture.
• Funding: not stated in the abstract.

Compared to antibiotics, cranberry products may make little or no difference to the risk of symptomatic, culture-verified UTIs (2 studies, 385 participants: RR 1.03, 95% CI 0.80 to 1.33; I2 = 0%)

NCCIH records that studies in women having gynaecological surgery and in people with multiple sclerosis did not find cranberry beneficial. (Source 8)

• Official position, Certainty not rated.
• Size: not stated on the page.
• Who: women undergoing gynaecological surgery; people with multiple sclerosis.
• How long: not stated.
• Result: no numbers given on the page.
• Funding: US government agency page.

Studies in other high-risk populations, such as women undergoing gynecological surgeries or people with multiple sclerosis, have not found cranberry to be beneficial in reducing the risk for UTIs.

POSITION: on 21 July 2020 the FDA concluded the cranberry-UTI evidence fell short of significant scientific agreement and allowed only a qualified health claim. (Source 9)

• Official position, Certainty not rated.
• Size: not applicable.
• Who: healthy women who have had a UTI.
• How long: not applicable.
• Result: claim wording restricted to 'limited' evidence for supplements and 'limited and inconsistent' for juice beverages.
• Funding: US federal regulator; petition filed on behalf of Ocean Spray Cranberries, Inc.

the FDA determined that the scientific evidence supporting the claim did not meet the 'significant scientific agreement' standard required for an authorized health claim, and the petitioner agreed to have the petition evaluated as a qualified health claim petition.

Where the evidence is mixed

A 2023 review of complementary approaches to kidney stones reports that human studies on cranberry and stone formation contradict each other. (Source 10)

• Expert review, not systematic, Very low certainty.
• Size: not stated; narrative summary of human studies.
• Who: uric acid and calcium oxalate stone formers.
• How long: not stated.
• Result: no pooled estimate; the review reports opposing directions of effect across studies.
• Funding: not stated in the abstract.

Some studies showed that uric acid or calcium oxalate stone formers are at risk when consuming cranberry products, while other studies have reported that consumption of large amounts of cranberry may reduce kidney stone formation.

Where the research disagrees

Whether the trial evidence is strong enough to say cranberry products prevent recurrent UTIs

• Cochrane review authors (Williams and colleagues, 2023), systematic review and meta-analysis of 50 randomised trials with GRADE certainty ratings: These data support the use of cranberry products to reduce the risk of symptomatic, culture-verified UTIs in women with recurrent UTIs, in children, and in people susceptible to UTIs following interventions. (Source 6)
• US Food and Drug Administration, letter of enforcement discretion for cranberry DIETARY SUPPLEMENTS, 21 July 2020, regulatory review of petitioned evidence against the significant scientific agreement standard: Limited scientific evidence shows that by consuming 500 mg each day of cranberry dietary supplement, healthy women who have had a urinary tract infection (UTI) may reduce their risk of recurrent UTI. (Source 11)

How much

• Reference intake: No reference intake (RDA or AI) exists for cranberry, because it is a food rather than an essential nutrient. The nearest official figure is the amount named in the FDA's 2020 qualified health claim for cranberry dietary supplements, 500 mg per day, which the FDA permits only with the statement that the supporting evidence is limited. (Source 11)
• Upper limit: No tolerable upper intake level or acceptable daily intake has been set for cranberry. NCCIH (November 2024) states only that oral cranberry is generally thought to be safe, while noting stomach upset and diarrhoea with very large amounts, particularly in young children. (Source 4)
• Studied: Trials in the 2023 Cochrane review used cranberry juice, tablets and capsules across low, moderate and high proanthocyanidin doses; the review could not demonstrate a dose-response. (Source 1)
• Studied: The FDA's 2020 qualified health claim refers to 500 mg per day of a cranberry dietary supplement in healthy women who have had a UTI. (Source 11)

A common belief, and what the research shows

The belief: Drinking cranberry juice or taking cranberry tablets will clear a urinary tract infection you already have.

What the research shows: The literature addresses prevention, not cure. NCCIH states: "While cranberry may assist in preventing symptomatic UTIs in some women, it isn't recommended as a treatment for existing UTIs in any population." and "People who think they have a UTI should see a health care provider for diagnosis and treatment. Don't use cranberry products instead of a proven treatment for a UTI." The Cochrane review's outcome was the occurrence of new infections: "cranberry products probably reduced the risk of symptomatic, culture-verified UTIs".

Questions and answers

What is it?

Cranberry is the berry of a low evergreen shrub from the wetlands of northern North America. It is sold as fresh and dried fruit, juice, and as dried extract in tablets and capsules. Supplement labels also list it as Vaccinium macrocarpon or as 'cranberry PACs'. (Source 8)

What does it do in the body?

The proposed mechanism is mechanical rather than antibiotic: proanthocyanidins are thought to stop bacteria attaching to the bladder lining, so an infection never gets started. This is a proposed mechanism, not a demonstrated one, and processing into tablets or capsules can strip out the PACs. (Source 8)

Is it good or bad for you?

It depends entirely on who is taking it and why. For women with recurrent UTIs and for children, the 2023 Cochrane review found moderate-certainty evidence of fewer culture-verified infections. For elderly people in institutions, pregnant women and people who do not empty their bladder fully, the same review found little or no benefit. Against that sits gastrointestinal upset, an increase in warfarin's effect in a crossover study, and widely variable product quality. (Source 5)

How do you get more of it?

Cranberry is obtained from the berries themselves, from cranberry juice beverages, and from dried extract capsules and tablets. The FDA's 2020 qualified health claim quoted here is the claim for cranberry dietary supplements, 500 mg per day, with the caveat that the supporting evidence is limited; it is not a claim about juice drinks, which the FDA treats separately. The 2023 Cochrane review could not show that higher proanthocyanidin doses worked better than lower ones. (Source 11)

If it is harmful, what reduces it?

Cranberry is not something the body accumulates, so there is nothing to clear. Where it causes trouble the reported trigger is quantity: very large amounts can cause stomach upset and diarrhoea, particularly in young children, and the reported effects settle when intake stops. People taking warfarin are the group where the interaction literature concentrates. (Source 4)

Why might someone be low in it or missing it?

Cranberry is not an essential nutrient, so there is no deficiency state and no literature on being 'low' in it. The variability that does exist is in the products: analysis of 24 European cranberry supplements found most failed the pharmacopoeia uniformity test, most declared the wrong PAC amount, and only five actually contained cranberry material. (Source 3)

We searched: Searched PubMed/PMC, Cochrane and NCCIH for cranberry deficiency, cranberry requirement and cranberry status; no literature defines a cranberry deficiency. The closest relevant literature is on product content variability.

Which whole foods contain it or feed it?

The whole food is the cranberry fruit itself, eaten fresh, dried or as juice; the leaves were also used traditionally. There is no other food source, and no food 'feeds' cranberry, since it is a plant product rather than something the body makes or hosts. (Source 8)

What happens if you do not have it?

Nothing is known to happen, because cranberry is not required by the body. Not taking it simply means not getting whatever reduction in recurrent UTI risk the trials found in the groups where a benefit was seen. The research base outside UTI prevention is thin. (Source 8)

We searched: Searched Cochrane, PMC and NCCIH for consequences of not consuming cranberry; no study addresses absence as an exposure. NCCIH notes how little research exists outside UTI prevention.

How can you test for it?

There is no blood or urine test for cranberry status, and no clinical test tells you whether a cranberry product is working. What the trials measured instead was the outcome: urine culture confirming a symptomatic urinary tract infection. Product PAC content can be measured in a laboratory, but that is a test of the product, not of the person. (Source 5)

We searched: Searched Cochrane 2023, PMC and NCCIH for a cranberry biomarker or cranberry status test; the reviews report culture-verified UTI as the outcome measure and no validated human marker of cranberry intake.

References

1. Cochrane Database of Systematic Reviews. Cranberries for preventing urinary tract infections - Abstract, Main results, gastrointestinal side effects and dose. 2023. DOI 10.1002/14651858.CD001321.pub7. Read the source
2. British Journal of Pharmacology. Pharmacodynamic interaction of warfarin with cranberry but not with garlic in healthy subjects. 2008. PMID 18516070, DOI 10.1038/bjp.2008.210. Read the source
3. Nutrients. Vaccinium macrocarpon (Cranberry)-Based Dietary Supplements: Variation in Mass Uniformity, Proanthocyanidin Dosage and Anthocyanin Profile Demonstrates Quality Control Standard Needed. 2020. PMID 32260055, DOI 10.3390/nu12040992. Read the source
4. National Center for Complementary and Integrative Health (NCCIH), NIH. Cranberry - Usefulness and Safety (What Do We Know About Safety?). 2024. Read the source
5. Cochrane Database of Systematic Reviews. Cranberries for preventing urinary tract infections (Cochrane Database of Systematic Reviews, Review) - Abstract, Main results. 2023. DOI 10.1002/14651858.CD001321.pub7. Read the source
6. Cochrane Database of Systematic Reviews. Cranberries for preventing urinary tract infections - Abstract, Authors' conclusions. 2023. DOI 10.1002/14651858.CD001321.pub7. Read the source
7. Cochrane Database of Systematic Reviews. Cranberries for preventing urinary tract infections - Abstract, Main results, comparisons with antibiotics and probiotics. 2023. DOI 10.1002/14651858.CD001321.pub7. Read the source
8. National Center for Complementary and Integrative Health (NCCIH), NIH. Cranberry - Usefulness and Safety (Background; How Much Do We Know?; What Have We Learned?). 2024. Read the source
9. U.S. Food and Drug Administration (Constituent Update, 21 July 2020). FDA Announces Qualified Health Claim for Certain Cranberry Products and Urinary Tract Infections. 2020. Read the source
10. Nutrients. Kidney Stone Prevention: Is There a Role for Complementary and Alternative Medicine?. 2023. PMID 36839235, DOI 10.3390/nu15040877. Read the source
11. U.S. Food and Drug Administration (Constituent Update, 21 July 2020). FDA Announces Qualified Health Claim for Certain Cranberry Products and Urinary Tract Infections - permitted dietary supplement claim wording. 2020. Read the source