The American cranberry (Vaccinium macrocarpon) is native to North America where it was traditionally used to treat bladder and kidney diseases. During the 17th century, cranberry was used to relief of blood disorders, stomach ailments, liver problems, vomiting, appetite loss, scurvy and cancer.
In the US about 20 percent of women have experienced urinary tract infections. Cranberry was used as a treatment of urinary tract infections and it was wrongly believed that cranberry acted by lowering the pH of urine. More recently, studies have shown that the action of cranberry is by preventing the attachment of bacteria to membranes. A recent review has shown that cranberry is not effective in treating urinary tract infections, but there is more evidence that cranberry can help to prevent the infection. The first clinical studies which showed that cranberry has preventive action appeared in 1994. On study showed that cranberry reduced the frequency of bacterial bladder infections and reduced pus in the urine. Another study showed that cranberry extract tablets were more effective than cranberry juice.
A large scale study carried out in 2001 involving 150 women showed that a juice from cranberry and lingonberry showed that this juice reduced the risk of urinary tract infections by 20 percent. A treatment with probiotics supplementation, containing lactobacillus, showed no effect. There are no clinical studies indicating that cranberry has other clinical effects but in vitro studies have shown that high molecular weight phytochemicals inhibits adherence of Escherichia coli and that cranberry juice has fungistatic effects. On the other hand, cranberry is a safe product without significant interaction with drugs.
The recommended dose is 300 to 400 mg cranberry extract twice daily or 250 ml unsweetened cranberry juice three times daily.
Source: Darren M. Lynch. Cranberry for Prevention of Urinary Tract Infections. American Family Physician 2004;70:2175-77