The medicinal properties of cranberry (Vaccinium macrocarpon) have been recognized for centuries. Native Americans used raw cranberries as a wound dressing. Early settlers from England learned to use the berry both raw and cooked for a number of ailments including appetite loss, digestive problems, blood disorders, and scurvy (vitamin C deficiency that causes weakness, gum disease, and spontaneous bleeding in the skin).

In the early 1920s, American scientists discovered that people who eat large amounts of cranberries have more acid in their urine than those who do not eat high amounts of the berry. Because bacteria cannot survive in an acidic environment, the researchers speculated that a diet rich in cranberries may help prevent and treat urinary tract infections (UTIs), which are commonly caused by bacteria known as Escherichia coli. In time, the popularity of cranberry for UTIs soared and many women reported satisfactory results from drinking cranberry juice. Although the scientific explanations for its purported benefits have changed throughout the years, there is a significant amount of evidence today to support the use of cranberries to prevent and treat UTIs.

Found primarily in North America and grown in bogs, cranberry is an evergreen shrub that is related to blueberry, buckberry, huckleberry, cowberry, and bilberry. The cranberry bush has upright branches with leaves that are speckled on the underside by tiny dots. Pink flowers blossom and red-black fruits appear during June and July.

The cranberry fruit is high in antioxidants, partly from substances called proanthocyanidins (which give cranberries their rich color). Antioxidants scavenge damaging particles in the body known as free radicals. Free radicals are natural by-products of normal metabolism. But, free radicals can alter cell membranes, tamper with genetic material known as DNA, and even cause cell death. Environmental toxins (including ultraviolet light, radiation, cigarette smoking, and air pollution) can increase the number of free radicals in the body, which are believed to contribute to the aging process as well as the development of a number of health problems such as heart disease, cancer, and infections. Antioxidants can neutralize free radicals and may reduce or even help prevent some of the damage they cause.

Several studies have measured high levels of antioxidants in people after drinking cranberry juice. Research is underway to determine if the antioxidant ability of cranberries will translate into protection from heart disease.

Proanthocyanidins also help prevent microorganisms from causing infections (such as UTIs) and appear to have cancer fighting properties. Cranberries are an excellent source of vitamin C as well, another important antioxidant.

The ripe fruit of the cranberry is the part used in commercial and medicinal preparations.

Cranberry is used to treat and prevent urinary tract infections of the bladder and urethra (the tube that drains urine from the bladder).

In one study of 192 elderly women, those who drank 300 mL (approximately 1 1/3 cups) of cranberry juice cocktail every day for 6 months had significantly less bacteria and infection in their urine than those who drank a placebo beverage for the same period of time. In another study of sexually active college students, regular consumption of cranberry juice was associated with a 50% reduction in UTIs.

Although used clinically for children with guidance from a qualified healthcare practitioner, the benefits of cranberries for UTIs in this age group are less clear. A preliminary study including only 15 children with neurogenic bladder (a bladder that does not empty properly, putting the child at particular risk for UTIs) found that cranberries were no more effective than placebo in reducing either the symptoms of UTI or the amount of bacteria in the urine for these children. Further studies are needed to best understand the application of cranberry juice for preventing or treating UTIs in children.

Cranberry also appears to be more effective than certain probiotics in preventing recurrent UTIs. (Probiotics are "friendly" bacteria that inhabit the intestines and vagina and protect against the entrance and proliferation of "bad" organisms that can cause disease. They are often used as a supplement to try to prevent or fight UTIs.) Researchers in Finland randomly assigned 150 women with recurrent UTIs to receive either a combined juice made from cranberries and lingonberries or a drink containing the probiotic Lactobacillus GG for up to one year. Women who drank the berry juice developed substantially fewer UTIs than those who consumed the probiotic beverage.

Interestingly, laboratory studies conducted in the mid 1990s revealed that the effectiveness of cranberry juice is not due to its ability to acidify the urine as originally thought, but to its ability to prevent E. coli (an organism that causes most UTIs) from adhering to the cells lining the wall of the bladder. Without adhering to the bladder, the researchers found, E. coli cannot flourish and cause a UTI. Test tube studies also suggest that cranberry juice may inhibit the adherence of other species of organisms that cause UTIs as well, such as Proteus, Klebsiella, and Pseudomonas.

Further laboratory studies indicated that cranberries also prevent another microorganism known as Helicobacter pylori from adhering to cell walls. H. plyori is a bacteria that can cause stomach ulcers, so it is possible that cranberries may eventually prove to play a role in the prevention of this condition. Studies also suggest that cranberries may help prevent bacteria from adhering to gums and around the teeth, but researchers caution that cranberry juice is high in sugar and should not be used for oral hygiene.

Cranberries are available fresh or frozen and in juice and concentrate forms. Dried berries are also available in tablet or capsule form. Pure cranberry juice is acidic and quite sour. Most commercial cranberry juices contain a mixture of cranberries, sweeteners (which may reduce the immune-boosting effects associated with the berry), and vitamin C. The addition of sweeteners to cranberry beverages may explain why cranberry juice cocktail and concentrate are not always effective in improving symptoms of UTI.

Pediatric

For minor urinary infections, the average recommended dosage for a 50 lb (20 to 25 kg) child is 0.5 L per day (16 ounces) of cranberry juice. Given that more research is needed regarding the specific effects of cranberries on UTIs in this age group, a child with a suspected or confirmed UTI should have his or her care directed by a qualified healthcare practitioner.

Adult

• Juice: 3 or more fluid ounces per day
• Capsules: 6 per day (equivalent to 3 fluid ounces of cranberry juice cocktail)
• Fresh or frozen cranberries: 1.5 ounces (equivalent to 3 fluid ounces of cranberry juice cocktail)

The use of herbs is a time-honored approach to strengthening the body and treating disease. Herbs, however, contain active substances that can trigger side effects and interact with other herbs, supplements, or medications. For these reasons, herbs should be taken with care, under the supervision of a practitioner knowledgeable in the field of botanical medicine.

Cranberry contains relatively high levels of oxalate, a substance that may increase the risk of kidney stones in people who are at risk for this condition. Individuals who are at risk for developing kidney stones, therefore, should consult a healthcare provider before taking cranberry supplements or drinking excessive amounts of cranberry juice.

Cranberry should not be used as a substitute for antibiotics during a serious UTI.

There are no known scientific reports of interactions between cranberry and conventional medications.

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