Get Involved
About Us
Our Members
Cranberry Effective in Preventing UTIs during Pregnancy and Lactation

Reviewed: Dugoua JJ, Seely D, Perri D, Mills E, Koren G. Safety and efficacy of cranberry (Vaccinium macrocarpon) during pregnancy and lactation. Can J Clin Pharmacol. 2008;15(1):e80-e86. Epub Jan 18, 2008.

Cranberry (Vaccinium macrocarpon, Ericaceae) is used for the treatment and prevention of urinary tract infections (UTIs), reflecting a traditional medicinal use by Native Americans. Proanthocyanidins (condensed tannins) in cranberry fruit prevent UTIs by preventing Escherichia coli from adhering to the wall of the urethra; the condensed tannins have been shown to be responsible for preventing uropathogenic phenotypes of P-fimbriated (mannose-resistant) E. coli from adhering to the urinary tract.1 Fructose in cranberry also has antibacterial effects. Pregnant women frequently use cranberry to prevent UTIs, which are more common among pregnant women. This review examines the safety and efficacy of cranberry in the prevention of UTIs among pregnant and lactating women.

The following databases were searched for literature on the safety, efficacy, and pharmacology of cranberry in pregnant and lactating women (inception to June 2006): AMED, CINAHL, Cochrane CENTRAL, Cochrane Library, Medline, Natural Medicines Comprehensive Database, and Natural Standard. The authors also searched the Complete German Commission E Monographs; no cranberry monograph was produced by the Commission E.2

The authors of this review have given cranberry fruit an evidence grade of “A” for prevention of UTIs, indicating “Very Strong Evidence.” Prevention of stomach ulcers, periodontal disease, and flu were given an evidence grade of “E” indicating “Indirect Evidence” from expert opinion or laboratory studies. For use and safety during pregnancy, cranberry fruit was labeled “3a” for “Weak Scientific Evidence” from one or more case series for common use and “5” for “Theoretical Evidence” based on theory or opinion for minimal risk when taken as food. For use during lactation, cranberry fruit was given a rating of “6” or unknown for “no available information” on potential for harm.

A survey of 400 Norwegian women has found that cranberry was the most commonly used herb during pregnancy.3 According to the authors, currently no published clinical studies have shown that cranberry is either safe or contraindicated during pregnancy and lactation. Cranberry does have a track record of safety as a food item. However, this does not mean “that the fruit (processed or not) is entirely safe in all populations or at high levels of consumption.” Consumption of cranberry tablets has been shown to increase urinary oxalates in healthy volunteers4 and consumption of up to 4 liters per day of cranberry juice may increase the risk of kidney stone formation (nephrolithiasis) in at-risk patients. It has also been demonstrated that infants and children who take over 3 liters per day of cranberry juice can develop gastrointestinal distress. It should be noted that 3 to 4 liters per day is an unusually large quantity of cranberry juice to consume.

Although cranberry has been shown to prevent UTIs through inhibiting bacterial adherence to the urinary tract, research has shown that it does not dislodge bacteria that have already adhered and started to colonize. Researchers have shown that cranberry juice has antibacterial effects against Escherichia coli, Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Proteus mirabilis. Cranberry has also been shown to inhibit the adherence of Helicobacter pylori to the stomach and to inhibit the adherence of plaque bacteria that cause periodontal disease. Other biological activities that have been attributed to cranberry include antiviral, antioxidant, and anticarcinogenic activities. There have been reports of interactions with warfarin, but a clinical trial has shown no alteration of the CYP2C9 enzyme that metabolizes the drug. An in vitro laboratory study has found that cranberry juice may inhibit CYP3A4, an enzyme that metabolizes the drug cyclosporine. However, a subsequent human clinical trial designed to test this possibility has found no interaction between cranberry juice and cyclosporine.

The authors of this review conclude that cranberry is effective in preventing UTIs in pregnant and breastfeeding women, except for those at risk of developing kidney stones. There is no direct clinical trial evidence of safety or harm in pregnant and lactating women, but a survey of 400 pregnant women has found no adverse effects with regular consumption.3 More research is needed on the anti-infective effects of cranberry “including improved oral hygiene, stomach ulceration, and the prevention of influenza.”

—Marissa Oppel, MS

  • Beachey EH. Bacterial adherence: adhesion-receptor interactions mediating the attachment of bacteria to mucosal surface. J Infect Dis. 1981;143:325–345.
  • Blumenthal M, Busse WR, Goldberg A, Gruenwald J, Hall T, Riggins CW, Rister RS, eds. Klein S, Rister RS, trans. The Complete German Commission E Monographs—Therapeutic Guide to Herbal Medicines. Austin, TX: American Botanical Council; Boston: Integrative Medicine Communications; 1998.
  • Nordeng H, Havnen GC. Use of herbal drugs in pregnancy: a survey among 400 Norwegian women. Pharmacoepidemiol Drug Saf. Jun 2004;13(6):371-380.
  • Terris MK, Issa MM, Tacker JR. Dietary supplementation with cranberry concentrate tablets may increase the risk of nephrolithiasis. Urology. 2001;57(1):26–29.