Women have long known that drinking cranberry juice is an excellent way to prevent or squash a urinary tract infection (UTI). Scientists have learned recently what makes this remedy so effective.

Researchers have been trying to figure out why cranberries are effective against UTIs from as early as the 1920s. There have been several theories—some have focused on the berry's acidity, others on its sugar. A recent 5-year study, done at Rutgers University, identified a substance in cranberries called tannins as the key to their infection-fighting ability. These tannins appear to prevent the bacteria that causes UTIs from attaching to the urinary tract. Blueberries are another fruit that contain tannins.

To lower your risk of getting a UTI, try drinking one 10-ounce glass of unsweetened cranberry juice every day. Or drink some juice as soon as you notice the symptoms of a UTI (symptoms include painful, burning, or frequent urination). If you dislike the juice, ask your pharmacist about cranberry extracts. Adding cranberries to your diet may be especially helpful if you are a woman with the following health conditions or lifestyle risk factors for UTIs:

• Diabetes
• Pregnancy
• Change in sexual partners or in frequency or intensity of sex
• Use of irritating chemicals, such as harsh skin cleansers
• Use of irritating contraceptive devices, such as a diaphragm or spermicides
• Use of birth control pills
• Heavy use of antibiotics
• A urinary tract abnormality or obstruction, such as a tumor
• Catheterization
• Use of chronic antimicrobial therapy, immunosuppressants, or corticosteroids

If you think you might have a UTI, check with your doctor. He or she may recommend other treatments or explore the possibility of other illnesses, such as sexually transmitted diseases, which can give you the same symptoms as a UTI. Meanwhile, adding cranberry juice to your diet may help manage your symptoms.