As a treatment for urinary tract infections (UTIs), cranberry (Vaccinium genus, several species, most often macrocarpon) has been studied scientifically since the early 1960s, although it has been used as a folk remedy for thousands of years. Amerindians of New England utilised the leaves of the plant, rather than the fruit, to treat urinary disorders, according to accounts by early European explorers. [1. Henig S and Leahy M 2000 Cranberry Juice and Urinary-Tract Health: Science Supports Folklore Y. Nutrition; 16 (7/8): 684-687.] In addition to many published reports of original research, there have been several reviews and meta-analyses published in recent years. Most of the studies of cranberry have utilised the fruit, most often in juice form, because of its high concentration of the A-type proanthocyanidins that are considered to be the active component of cranberry in relation to UTIs. [2. Blumberg JB, Camesano TA, Cassidy A, Kris-Etherton P, Howell A, Manach C, Ostertag LM, Sies H, Skulas-Ray A, Vita JA. 2013. Cranberries and their bioactive constituents in human health. Adv Nutr.; 4(6):618-32.]
UTIs occur much more often in women than men, and populations that are particularly susceptible include pregnant women, elderly women, patients with neuropathic bladder and patients with spinal cord injury, especially those who are catheterised. [3. Wang CH1, Fang CC, Chen NC, Liu SS, Yu PH, Wu TY, Chen WT, Lee CC, Chen SC. 2012 Cranberry-containing products for prevention of urinary tract infections in susceptible populations: a systematic review and meta-analysis of randomized controlled trials. Arch Intern Med.;172(13):988-96. ], [4. Raz R. 2011 Urinary tract infection in postmenopausal women. Korean J Urol.;52(12):801-8.] The mechanism of action of the active ingredient in cranberry is the inhibition of adherence of E. coli, the most common cause of UTIs, to epithelial cells of the urinary tract. [5. Risco E1, Miguélez C, Sánchez de Badajoz E, Rouseaud A. 2010 Effect of American cranberry (Cysticlean) on Escherichia coli adherence to bladder epithelial cells. In vitro and in vivo study. Arch Esp Urol.;63(6): 422-30.], [6. Howell A, Souza D, Roller M, Fromentin E. 2015 Comparison of the Anti-Adhesion Activity of Three Different Cranberry Extracts on Uropathogenic P-fimbriated Escherichia coli: a Randomized, Double-blind, Placebo Controlled, Ex Vivo, Acute Study. Nat Prod Commun.;10(7):1215-8.]
In a systematic review of the efficacy of cranberry-containing products in susceptible populations, Wang et al. (2012) examined the results of thirteen trials involving 1616 subjects, with ten of the 13 conducted in N. America. 3 In a comparison of cranberry users vs. non-users in nine of the ten N. American trials they reviewed, they reported a risk ratio of 0.62, i.e. users have only 0.62 times the risk for UTIs that non-users do. In other words, the risk of a UTI in users is 38% less than in non-users. Jepson et al. (2008), in a report on a Cochrane review (Cochrane produces systematic reviews of primary research in human health care which are internationally recognized as the highest standard in evidence-based health care resources), noted that the risk ratio for cranberry juice in the prevention of systematic UTIs was 0.66 in the general population, and 0.61 in women with recurrent UTIs. [7. Jepson RG, Craig JC.2008 Cranberries for preventing urinary tract infections. Cochrane Database Syst Rev.;(1): CD001321.]
Another internationally-recognised organisation tasked with producing wide-ranging reviews of natural products is Natural Medicines, located in Somerville, MA, USA. In their research on studies involving cranberry juice and UTIs, they reported that “drinking cranberry juice or taking certain cranberry extracts can reduce the risk of recurrent UTI in some patients. Cranberry products also seem to be effective at reducing the risk of UTIs in women in general, while cranberry juice cocktails may be effective at reducing the risk of UTIs in children, in elderly women, in pregnant women, and in hospitalized inpatients.” [8. https://naturalmedicines.therapeuticresearch.com/databases/food,-herbs-supplements/professional.aspx?productid=958#scientificName] However, they did review many of the same studies reviewed by Wang et al., including Wang’s own study.