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, stomach problems, blood disorders, and scurvy, caused by not getting enough vitamin C.
Cranberry is best known for preventing urinary tract infections (UTIs), commonly caused by bacteria known as Escherichia coli (E. coli). At first, 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. Strong scientific studies support using cranberry, either in capsules 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 underneath 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. Scientists are researching to see if the antioxidant ability of cranberries will help protect against heart disease and cancer.
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 frequent UTIs. In one study of older women, cranberry juice reduced the amount of bacteria in the bladder compared to placebo. Another study showed that younger women with a history of frequent UTIs who took cranberry capsules had fewer UTIs compared to those who took placebo.
However, studies suggest that cranberry doesn’t work once you have a UTI. That’s because in preventing UTIs, it helps keep bacteria from attaching to the urinary tract. But it’s less effective once the bacteria have already attached. For this reason, cranberry is more effective at preventing UTIs than treating them. UTIs should be treated with conventional antibiotics.
Two studies that cranberry may also prevent the bacteria Helicobacter pylori from attaching to stomach walls. H. pylori can cause stomach ulcers, so cranberries may play a role in the preventing stomach ulcers. More research is needed.
Cranberry is also being studied for the following conditions, although there isn’t enough evidence yet to tell whether it helps prevent or treat them:
Alzheimer’s disease -- In laboratory tests, cranberry seems to protect somewhat against Alzheimer’s disease. Studies in people are needed.
Cancer -- Some test tube and animal studies suggest cranberry may help stop cancer cells from growing.
Inflammation -- In the laboratory, cranberry has anti-inflammatory effects.
High cholesterol -- One preliminary study found that drinking cranberry juice raised HDL “good” cholesterol levels.
Viruses -- Cranberry seems to fight some viruses in test tubes. Studies in people are needed.
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 is generally considered safe with no serious side effects, even for pregnant women. Cranberry supplements are considered safe for most people, although pregnant and breastfeeding women should ask their doctor before taking any supplement, including cranberry.
Cranberry contains relatively high levels of oxalate, chemicals that may raise the risk of kidney stones in some people. If you have kidney stones, talk to your doctor before taking cranberry supplements or drinking a lot of cranberry juice.
Don’t use cranberry if you already have a UTI. You should see a doctor for prescription antibiotics.
Because most cranberry juice contains added sugar, people who have diabetes should look for brands that are artificially sweetened or should be careful how much sweetened juice they drink.
People who are allergic to aspirin may also be allergic to cranberry.
Warfarin (Coumadin) -- Cranberry may raise the risk of bleeding, especially if you already take medications to thin the blood such as warfarin. The evidence is mixed and not completely clear, so it’s best to ask your doctor before you take cranberry or drink a lot of juice.
Aspirin -- Like aspirin, cranberries contain salicylic acid. If you take aspirin regularly -- as a blood-thinner, for example -- or if you are allergic to aspirin, you should not take cranberry supplements or drink a lot of juice.
Other medications -- Cranberry may interact with medications that are processed by the liver. If you take any medications, ask your doctor before taking cranberry.
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