For centuries, indigenous people have used cranberry for the treatment of UTIs and other ailments. Modern scientific research has validated this traditional usage by revealing an active component in cranberry that possesses this antimicrobial effect. Howell et al. (1998) discovered that cranberries contain flavonoids called proanthocyanidins (PACs) that can prevent P-fimbriated Escherichia coli (E. coli) bacteria from adhering to the uroepithelial cells in the urinary tract and proliferating to cause UTIs. A subsequent 2005 study reported that other foods containing PACs do not exhibit the anti-adhesion activity that cranberry demonstrates. It was determined that high molecular weight cranberry PACs exhibit a unique A-type intermolecular double linkage that enables cranberry to possess this special microbial anti-adhesion property. In a 2009 human study comparing cranberry and an antibiotic, the researchers concluded that the antibiotic had a very limited advantage over cranberry extract in the prevention of recurrent UTIs and had more adverse effects (McMurdo et al.). A collaborative human study (Howell et al., 2002) found that cranberry even prevented the adhesion of antibiotic-resistant strains of E. coli. There was enough compelling evidence of the anti-bacterial adherence quality of cranberry that the French Agency for Food Safety (AFSSA) approved a claim in 2004 that states 36mg of proanthocyanidins (as measured by what is now called the BL-DMAC method) “helps to reduce the adherence of certain E. coli bacteria to the urinary tract walls.” Numerous studies, ranging from in vitro to human clinical studies, have further validated the role of cranberry for combating UTIs, including a 2011 study on children with recurrent UTIs (Kontiokari et al.), and 2009 Cochrane review that concluded “there is some evidence that cranberry juice and derivatives are effective in preventing UTIs in women with recurrent UTIs.”
Given the anti-adhesion properties cranberry has shown in studies with E. coli, researchers studied the effect of the proanthocyanidins (PACs) from cranberries in in vitro adhesion studies using Helicobacter pylori (H. pylori). This spiral bacteria is responsible for gastrointestinal diseases including gastric, duodenal, and peptide ulcers. Research by Burger et al. (2002) showed the cranberry PACs inhibited adhesion to human gastric mucosal cells in a dose dependent manner, suggesting protective effects that may prevent the development of H. pylori-induced stomach ulcers. Another possible mechanism involves the ability to cranberry to cause H. pylori to develop a coccoid form, thereby inhibiting its proliferation (Matsushima et al., 2008). In 2005, Kontiokari et al. evaluated the colonic bacteria flora in children and determined that cranberry juice did not adversely affect the healthy bacterial gastrointestinal flora. A 2007 clinical study by Shmuely et al. revealed that women who drank cranberry juice along with antibiotics experienced enhanced eradication of H. pylori infection.
New evidence suggests that the same antiadhesion activity of cranberry PACs that contributes to the prevention of UTIs and stomach ulcers may also be helpful in the prevention of periodontal disease. Yamanaka et al. (2007) investigated cranberry’s ability to inhibit growth and biofilm formation of Streptococci mutans strains as well as the enzyme activity and biofilm formation of P. gingivalis. They concluded that oral health products using cranberry polyphenols may prevent the development of dental plaque. In 2010, the specific PACs in cranberry were indicated for the treatment of periodontal disease because of their ability to affect the etiology of periodontitis. Additional reviews (Bodet et al., 2008; Bonifait et al., 2010) discuss the positive role of cranberry in the prevention and/or treatment of dental caries and periodontal disease. Cranberry’s role in immune support is a topic of increasing interest and a 2010 clinical study by Nantz et al. showed that cranberry phytochemicals modified human immune function and reduced the severity of cold and flu symptoms.
Clinical studies (Ruel et al., 2005, 2008; Lee et al., 2008; Basu et al., 2011; Dohadwala et al., 2011) have shown that ingestion of cranberry resulted in decreases in oxidized LDL cholesterol as well as atherosclerotic cholesterol profiles, arterial stiffness, and certain inflammatory markers— all risk factors for cardiovascular disease. Additionally, researchers concluded that dried cranberry juice significantly decreased serum levels of advanced oxidative protein products, indicating a protective effect against oxidative damage (Valentova et al., 2007).