Cranberry

Vaccinium macrocarpon Aiton belongs to Ericaceae, the heath family, alongside blueberries, rhododendrons, and mountain laurels; NCBI Taxonomy files it as taxon 13750, and some botanists place it in a separate genus as Oxycoccus macrocarpus. The species name means large-fruited, distinguishing it from the small or European cranberry, Vaccinium oxycoccos, which the University of Massachusetts Cranberry Station notes is not cultivated in North America. Flora of North America gives its habitat as bogs, swamps, mires, and wet shores, and UMass describes a native range from Maine and the Atlantic Provinces to northern Illinois, and south to Tennessee at high elevations. It is introduced and escaping in British Columbia, Oregon, and Washington. Like its relatives it needs acid soil, around pH 4 to 5. The plant is a low, trailing, woody evergreen vine whose runners grow one to six feet long. The small, leathery leaves, 5 to 15 mm long, turn reddish-brown from October to April. The fine, shallow roots lack root hairs and rely on ericoid mycorrhizal fungi to take up organic nitrogen (UMass).

Short vertical shoots called uprights, two to eight inches tall, rise from buds along the runners and carry most of the flowers and fruit. Each fruit bud holds two to seven flowers, which in Massachusetts open from mid-June over three to six weeks (UMass). The flowers hang on slender, nodding stalks, and their white to pink petals are swept sharply backward, exposing a dark cone of fused stamens (Flora of North America; NC State Extension). UMass explains that the flower’s stem and blossom were said to resemble the neck and head of a crane, giving the name craneberry, later shortened to cranberry; Caruso and colleagues (American Phytopathological Society 2000) add that cranes may simply have liked the fruit. The flowers are self-fertile, but cross-pollination produces bigger berries with more seeds, so growers bring in honey bees and bumble bees. Berries ripen about 80 days after full bloom and are red, 9 to 14 mm across (Flora of North America). Caruso and colleagues note that each berry has four chambers containing air, which is why cranberries float, a property the industry relies on at harvest.

The compounds that interest researchers are proanthocyanidins, chains of flavan-3-ol units such as epicatechin. Foo and colleagues (Journal of Natural Products 2000) isolated PAC trimers with A-type linkages from ripe cranberries that blocked the adhesion of urinary E. coli, while the dimer procyanidin A2 (PubChem CID 124025, C30H24O12) was only weakly active and the B-type dimer procyanidin B2 was inactive. Procyanidin A2 is now the reference standard for the DMAC method, a color test validated in five laboratories for measuring PACs in cranberry powders (Prior and colleagues, Journal of the Science of Food and Agriculture 2010). On farms, beds are sanded every three to four years to encourage new roots and uprights, and Caruso and colleagues stress that, contrary to popular belief, they are not constantly flooded. More than 90% of Massachusetts cranberries are wet-harvested: the beds are flooded, and the floating berries are corralled with booms and removed by conveyor or vacuum (UMass). In 2025, USDA figures show, the United States produced about 7.5 million barrels of 100 pounds each, 4.6 million of them in Wisconsin and 1.9 million in Massachusetts, with smaller crops in New Jersey and Oregon.

Wild cranberries were gathered long before anyone farmed them. The Cape Cod Cranberry Growers’ Association says the Wampanoag people have harvested sasumuneash, wild cranberries, for some 12,000 years, eating them fresh and in nasampe and pemmican. Caruso and colleagues give the Narragansett name as sasemineash, describe pemmican as dried meat or fish pounded with berries and dried in the sun, and credit Native Americans with the first sweetened cranberry sauce, made with maple sugar. Indigenous peoples used the juice as a dye for blankets and rugs and the fruit as a poultice for wounds and, mixed with cornmeal, as a poultice for blood poisoning (Caruso; EMA assessment report). Accounts of other healing uses differ: the growers’ association says Wampanoag healers used cranberries for fever, swelling, and seasickness, while EMA’s assessors found no recorded medicinal use among Massachusetts tribes in the literature they reviewed. EMA lists seventeenth-century colonial uses for blood disorders, stomach and liver complaints, fevers, vomiting, appetite loss, and scurvy, and Caruso notes that sailors ate cranberries from barrels on long voyages to prevent scurvy, much as British sailors used limes.

Commercial cultivation began on Cape Cod. According to Caruso and colleagues, Henry Hall, a Revolutionary War veteran and ship’s captain in North Dennis, Massachusetts, noticed that the most vigorous wild vines near his home were those that received dune sand blown by northeast winds, and in 1816 he transplanted vines into a drained, sanded plot behind his house (UMass and the growers’ association also date his work to 1816). By 1820 he was shipping cranberries to Boston and New York. Cultivation spread to New Jersey in 1835, Wisconsin in 1853, and Oregon and Washington in the late 1800s. The 100-pound barrel became the industry’s unique unit of measure, and water harvesting, which began with shallow floods in Wisconsin in the 1920s, became the norm after deeper floods were adopted in the early 1960s. The growers’ association records that as late as 1927 Massachusetts children could be excused from school to work the harvest. The industry reached a low point after the 1959 aminotriazole scare, when the US Secretary of Health, Education, and Welfare publicized that some berries were tainted with a herbicide suspected of causing cancer; only a minimal acreage in Oregon was affected, but cranberries had to be destroyed, prices fell, and the industry did not rebound until the late 1960s (Caruso).

The urinary story began with chemistry. EMA’s assessment report records that German physicians in the mid-1800s noticed that eating cranberries increased urinary hippuric acid, which was believed to be antibacterial. Blatherwick (1914) attributed this to benzoic acid in the fruit being excreted as hippuric acid and acidifying the urine, and later researchers pointed to quinic acid as the source. The theory faded once studies showed that juice changed urine pH only briefly and rarely produced enough hippuric acid to stop bacteria growing. In 1984 Sobota proposed a different mechanism, anti-adherence activity in urine, and Howell and colleagues (New England Journal of Medicine 1998) linked it to cranberry proanthocyanidins. Cochrane first reviewed cranberry for UTI prevention in 1998 and has updated the review five times, most recently in 2023. In 2020 the FDA, responding to a petition submitted on behalf of Ocean Spray Cranberries, concluded that the evidence did not meet the significant scientific agreement standard for a full health claim and instead allowed qualified claims.

E. coli causes most UTIs, and to cause an infection the bacteria must attach to the cells lining the urinary tract; strains carrying hair-like P fimbriae latch onto sugar receptors on those cells. The leading explanation for cranberry, summarized by Howell and colleagues (BMC Infectious Diseases 2010), is that its PACs, particularly those with A-type linkages, inhibit the adhesion of P-fimbriated E. coli to these cells. In laboratory tests, Foo and colleagues found that A-type PAC trimers from cranberry prevented urinary E. coli from adhering to surfaces carrying the same alpha-Gal(1→4)beta-Gal receptor sequence found on bladder cells. Howell and colleagues (Phytochemistry 2005) then compared PACs from different foods. A-type PACs from cranberry blocked adhesion at 60 micrograms per milliliter, B-type PACs from grape showed minor activity only at 1,200, and PACs from apple, green tea, and dark chocolate were inactive. Urine collected after people consumed cranberry showed anti-adhesion activity, but urine collected after the other foods did not. Anti-adhesion does not kill bacteria, which fits with cranberry being studied for prevention rather than for treating an established infection.

Dose has been harder to pin down. In their randomized, double-blind study of 32 volunteers from Japan, Hungary, Spain, and France, Howell and colleagues found that anti-adhesion activity in urine rose with the amount of PACs in a cranberry powder and lasted up to 24 hours at 72 mg a day. Measuring PACs is itself tricky. The DMAC method gave consistent results within each laboratory but varied by about 17% between laboratories, and its developers caution that it suits comparisons within cranberry products rather than across different foods (Prior). Capsules registered as traditional herbal medicines in several EU countries supply 36 mg of PACs, calculated as procyanidin A2 (EMA assessment report), the same strength as each capsule in the Juthani-Mehta nursing-home trial (see uses). Yet the Cochrane review found no difference in UTI risk between low, moderate, and high PAC doses, and rated the evidence comparing doses, or juice with tablets, as very low certainty. NCCIH notes that processing cranberries into tablets or capsules can reduce their PAC content.

The older acidification theory has not held up. EMA’s assessors note that although cranberry juice itself is very acidic, around pH 2.3, it changed urine pH only temporarily, for 10 to 15 minutes in most people, and only occasionally supplied enough hippuric acid to reach bacteriostatic concentrations. In a controlled metabolic study, Gettman and colleagues (Journal of Urology 2005) gave 24 people a liter of cranberry juice a day for a week, and urine pH fell only from 5.97 to 5.67, although that acid load, together with other changes in the urine, matters for kidney stones (see side effects). Cranberry has been tested against other microbes too, and MSKCC notes that its reported effects on H. pylori and on the bacteria of dental plaque come mostly from laboratory studies. How cranberry might affect warfarin is unclear. One suggested route is the drug-metabolizing enzyme CYP2C9, but MSKCC notes that cranberry’s CYP2C9 inhibition in the laboratory was not seen in people, and controlled studies found no change in warfarin blood levels (Ansell; Mohammed Abdul).

Preventing recurrent UTIs is the main use, and the best evidence comes from Williams and colleagues (Cochrane 2023), a review published in April 2023 and revised that November. It included 50 randomized trials with 8,857 participants. In the 26 trials that could be pooled, cranberry products reduced symptomatic, culture-confirmed UTIs by about 30% compared with placebo or no treatment (risk ratio 0.70; 6,211 participants; moderate certainty), though results varied considerably between trials. The benefit was probable in women with recurrent UTIs (risk ratio 0.74, with a confidence interval from 0.55 to 0.99; 8 trials, 1,555 women), in children (0.46; 5 trials, 504 children), and in people susceptible to UTIs because of a medical intervention (0.47; 6 trials, 1,434 people). Two trials comparing cranberry with preventive antibiotics found little or no difference in UTIs, and compared with probiotics cranberry may have done better. A relative reduction of a quarter to a half is worthwhile for someone who gets several infections a year, but it does not prevent every infection.

The change from Cochrane’s 2012 conclusion deserves an honest explanation. Jepson and colleagues then pooled 24 studies with 4,473 participants and found no significant reduction in symptomatic UTIs overall (risk ratio 0.86, with a confidence interval from 0.71 to 1.04) or in women with recurrent UTIs. They highlighted low compliance and high dropout rates, mainly because people struggled to keep drinking juice, and noted that most tablet and capsule studies did not report how much active ingredient their products contained. The 2023 update added 26 newer trials. Individual trials still disagree. In 319 college women with an acute UTI, Barbosa-Cesnik and colleagues (Clinical Infectious Diseases 2011) found that 8 ounces of 27% cranberry juice twice daily did not prevent a second infection over six months: 20.0% had a recurrence with cranberry and 14.0% with placebo. Maki and colleagues (American Journal of Clinical Nutrition 2016), in a trial with co-authors from Ocean Spray, randomized 373 women with a recent UTI to a 240 mL cranberry beverage or placebo daily for 24 weeks; clinical UTIs fell from 67 to 39 episodes, but the time to a culture-confirmed UTI did not differ.

Cranberry has not helped every group at risk. In a year-long trial in 21 Connecticut nursing homes, Juthani-Mehta and colleagues (JAMA 2016) gave 185 women aged 65 and over two capsules a day containing 72 mg of PACs in total, described as equivalent to 20 ounces of juice, or placebo. Bacteria plus white cells in the urine were found in 29.1% and 29.0% respectively, and symptomatic UTIs (10 versus 12 episodes) did not differ. The Cochrane review likewise found little or no benefit in older people in institutions, in pregnant women, and in adults with nerve-related bladder problems who cannot empty the bladder fully, and NCCIH notes that studies in women having gynecological surgery and in people with multiple sclerosis did not find a benefit. Cranberry is also not a treatment for an infection that has already started: NCCIH says it is not recommended as a treatment for existing UTIs in any population, and EMA’s monograph tells users to see a doctor if symptoms persist for more than four days or if fever, painful urination, spasms, or blood in the urine appear.

Regulators and guideline writers have made cautious room for cranberry. The FDA’s 2020 letter of enforcement discretion lets juice beverages containing at least 27% cranberry juice say that limited and inconsistent evidence shows one 8-ounce serving a day may reduce the risk of recurrent UTI in healthy women who have had a UTI, and lets supplements containing at least 500 mg of cranberry fruit powder make a similar claim on limited evidence; dried cranberries and cranberry sauce are excluded. The 2019 guideline of the American Urological Association, with Canadian and urodynamics specialist societies, said clinicians may offer cranberry to women with recurrent UTIs, a conditional recommendation on low-grade evidence, and its 2025 update moved to saying clinicians should offer cranberry as an option, a moderate recommendation on Grade B evidence. EMA’s assessment report notes that the European Association of Urology, in its 2018 and 2020 guidelines, made no recommendation because of conflicting trials. EMA itself accepts cranberry juice only as a traditional herbal medicine for women, based on long use rather than proven efficacy, to relieve mild recurrent lower urinary symptoms or to help prevent recurrent uncomplicated lower UTIs.

Other uses are much less established. For H. pylori, a stomach bacterium that is a major cause of peptic ulcers, Zhang and colleagues (Helicobacter 2005) found that 14 of 97 adults drinking two 250 mL boxes of cranberry juice a day tested negative after 90 days, against 5 of 92 on placebo. In 522 infected adults in China, Li and colleagues (Journal of Gastroenterology and Hepatology 2021) found that 20% of those drinking high-PAC juice twice daily tested negative at eight weeks, against about 7% on placebo, while capsules of cranberry powder had no significant effect; a 2022 meta-analysis of four trials found no statistically significant effect on eradication (Nikbazm, British Journal of Nutrition). Cranberry is no substitute for prescribed eradication therapy. For heart and metabolic health, a 2024 meta-analysis of 16 trials found small improvements in the ratio of total to HDL cholesterol and in insulin resistance, but no change in LDL cholesterol, fasting glucose, or HbA1c (Li, Nutrients), and a 2026 meta-analysis of 12 trials found no significant effect on blood pressure (Bahreyni, Clinical Cardiology). MSKCC notes that effects on dental plaque bacteria and cancer cells have been shown only in the laboratory.

Cranberry comes in three broad forms, and trial results do not transfer neatly between them. Juice cocktails are sweetened drinks; the FDA notes that most commercially available cocktails contain at least 27% cranberry juice, the minimum for its qualified claim. Barbosa-Cesnik’s negative trial used 8 ounces of 27% juice twice daily, while Maki’s positive trial used one 240 mL serving of a cranberry beverage a day. Capsules and tablets contain dried fruit powder or concentrated extract: the FDA claim applies to at least 500 mg of cranberry fruit powder a day, the Juthani-Mehta trial used 72 mg of PACs a day, and capsules registered in several EU countries supply 36 mg of PACs. EMA’s traditional-use monograph covers only juice pressed from the fresh fruit, at 30 mL once daily to prevent recurrent uncomplicated lower UTIs in women, or 50 to 60 mL two to four times daily to relieve the symptoms of mild recurrent lower UTIs. Cochrane could not tell whether juice or tablets work better.

Sugar matters if you plan to drink juice every day. USDA FoodData Central lists about 11 to 12 grams of sugar per 100 grams of cranberry juice cocktail, close to 30 grams in an 8-ounce glass, while a diet cranberry drink it lists contains almost none. Capsules avoid the sugar and calories altogether. Product labels need careful reading: a capsule may state milligrams of cranberry powder, milligrams of extract, or milligrams of PACs, and PAC figures measured by different methods are not directly comparable (Prior). Because the Cochrane review found no clear difference between PAC doses, a higher dose is not obviously better, and no PAC dose has been shown in clinical trials to be the right one.

Practical points: cranberry is a long-term preventive, and most controlled trials ran for six to twelve months (EMA assessment report), so it is fairest to judge it over several months by counting infections rather than by how you feel day to day. Choose a form you can keep taking, since in older juice trials many people gave up. Anyone who develops urinary symptoms while taking cranberry should be assessed rather than increasing the dose. EMA advises against cranberry medicines in men, in pregnancy, and under 18, because urinary symptoms in men and pregnant women need medical supervision and data in young people are insufficient. If you take warfarin or tacrolimus, or have had kidney stones, read the cautions below before starting.