The juice from cranberries, also called Vaccinium macrocarpon, has been consumed for centuries, both for its refreshing tart taste and for its reported medicinal qualities. Although cranberry juice has not been shown to treat urinary tract infections, also called UTIs, many research studies have shown that this juice is effective in preventing this type of infection.
UTI-Causing Bacteria
UTIs are infections of the bladder, which holds urine, or the urethra, which is the tube that carries urine from the bladder to outside of the body. These infections are usually caused by the bacteria Escherichia coli, commonly abbreviated E. coli. These bacteria normally live in the digestive tract, in the vagina of women, and/or around the urethra. The bacteria commonly get deposited in the urethra through sex or by wiping after urination.
Prevents Bacterial Attachment
Researchers first believed that the mechanism by which cranberry juice prevents UTIs was by increasing the acidity level of urine. According to this theory, the growth of bacteria is inhibited due to the higher acid content of urine. However, scientists now think that the UTI preventive nature of cranberry juice is mediated by inhibition of bacterial attachment to the walls of the bladder. Because the bacteria cannot easily attach to the bladder, they are easily flushed out when the bladder is emptied.
Flushes Out Bacteria
Another way that cranberry juice helps prevent UTIs is by encouraging regular emptying of the bladder. Frequent voiding of the bladder helps flush bacteria out of the urinary tract, which is especially effective when the cranberry juice has altered the bladder wall so that bacteria cannot effectively attach to it.
Considerations
Although there have been many studies that have investigated the effectiveness of cranberry juice in preventing UTIs, MayoClinic.com reports that many of these studies were poorly designed and not well-controlled. However, they do acknowledge that considering all the research conducted in total does indicate that cranberry juice is effective in preventing UTIs.
Precautions
Cranberry juice is considered generally safe for otherwise healthy adults, including pregnant women. One consideration with respect to side effects is for people who are prone to kidney stones, as one component of cranberry juice, oxalate, increases the risk of developing these painful stones. Additionally, the tartness of cranberries leads many manufacturers to add a large amount of sugar to cranberry juice, and thus those watching calorie and sugar intake should factor in the added sugar of this juice.
Recommendations
The University of Maryland Medical Center recommends that adults who want to prevent UTIs should drink 3 oz. or more of cranberry juice per day. If you prefer to drink cranberry cocktail instead, 10 oz. or more is recommended.
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