Cranberry (Vaccinium macrocarpon ) has been used as both a food and a medicine for centuries. It is native to North America and was used by Native Americans to treat bladder and kidney diseases. Early settlers from England learned to use the berry both raw and cooked for many ailments, including appetite loss, digestive problems, blood disorders, and scurvy (vitamin C deficiency).
Cranberry is best known as a preventive treatment for urinary tract infections (UTIs), commonly caused by bacteria known as Escherichia coli (E. coli). Originally, scientists thought cranberry worked by making urine acidic enough to kill the bacteria. Now, studies show that cranberry actually prevents bacteria from attaching to the walls of the urinary tract. Valid scientific studies support the use of cranberry (taken as a supplement or as juice) for preventing -- though not treating -- UTIs.
Found primarily in North America and grown in bogs, cranberry is an evergreen shrub related to blueberry, buckberry, huckleberry, 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.
Cranberry fruit is high in antioxidants, partly from substances called proanthocyanidins (which give cranberries their vibrant color). Antioxidants neutralize particles in the body known as free radicals, which damage cell membranes, tamper with DNA, and even cause cell death.
Cranberries are also an excellent source of vitamin C, another important antioxidant. Research is underway to determine if the antioxidant ability of cranberries will help protect against heart disease and cancer.
The ripe fruit of the cranberry is the part used in commercial and medicinal preparations.
Medicinal Uses and Indications
Urinary tract infections
Several studies indicate that cranberry helps prevent UTIs of the bladder and urethra (the tube that drains urine from the bladder), particularly for women who have recurrent UTIs. In one study of older women, cranberry juice significantly reduced the amount of bacteria present in the bladder compared to placebo. Another study showed that younger women with a history of recurrent UTIs who took cranberry by capsule significantly reduced the recurrence of UTI compared to those who took placebo.
However, evidence suggests that cranberry is not as effective against bacteria once they have attached to cells in the urinary tract. For this reason, cranberry is more effective at preventing UTIs than treating them. UTIs should be treated with conventional antibiotics.
A preliminary study suggests that cranberry may also prevent the bacteria Helicobacter pylori from attaching to stomach walls. H. pylori can cause stomach ulcers, so it is possible that cranberries may play a role in the prevention of this condition. More research is needed.
The antioxidants found in cranberry may protect from heart disease by lowering LDL ("bad") cholesterol, relaxing blood vessels, and preventing plaque from building up in arteries. More research is needed.
In some test tube studies, cranberry appears to inhibit the growth of cancer cells. It is too early to say whether the herb will have the same effect in humans.
Studies also suggest that cranberries may help prevent bacteria from adhering to gums and around the teeth, helping to prevent cavities. Researchers caution, however, that cranberry juice is usually 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 very sour, so most cranberry juices contain a mixture of cranberries, sweeteners (which may reduce the healthful effects of the juice), and vitamin C. Look for a brand of cranberry juice that has the lowest amount of added sugar or is sugar-free.
How to Take It
There is not enough evidence to establish a safe dose for children prone to UTIs. A child with a UTI should be under the care of a qualified health care provider.
- Juice: 3 or more fluid oz. of pure juice per day, or about 10 oz. of cranberry juice cocktail
- Capsules: 300 mg to 400 mg, 6 per day in divided doses
- Fresh or frozen cranberries: 1.5 ounces
The use of herbs is a time-honored approach to strengthening the body and treating disease. Herbs, however, can trigger side effects and can interact with other herbs, supplements, or medications. For these reasons, herbs should be taken with care, under the supervision of a health care provider.
Cranberry juice and supplements are generally considered safe with no serious side effects, even for pregnant women.
Cranberry contains relatively high levels of oxalate, chemicals that may increase the risk of kidney stones. People who have or have had kidney stones should talk to their doctor before taking cranberry supplements or drinking large amounts of cranberry juice.
Cranberry should not be used as a substitute for antibiotics during a UTI.
Because most cranberry juice contains added sugar, people who have diabetes should look for brands of juice that are artificially sweetened or should limit their consumption of regular juice.
A preliminary report suggests that cranberry may interfere with the effects of the blood-thinning drug warfarin. If you take warfarin, do not take supplemental cranberry and limit your consumption of cranberry juice.