Cranberry juice is renowned for its effectiveness in treating urinary tract infections because it inhibits bacteria from attaching to the bladder and urethra. How does the same premise prevent cavities and gum disease? Another gram-negative bacteria, streptococcus mutans, keeps plaque from sticking to the surface of your teeth. This is a perfect example of how some bacteria in the body can be good.
Antioxidants and phytonutrients in cranberries, such as oligomeric proanthocyanidins, anthocyanidin flavonoids (which give them their bright red color), cyanidin, peonidin, and quercetin, have unique health-impacting attributes. (Scientists say it's possible that the anthocyanidin strength in cranberries is increased when they're water-harvested, due to the amount of natural sunlight they're exposed to.) Some contain stroke- and cardiovascular disease-preventing compounds that discourage cholesterol from forming in the heart and blood vessels.
Research bears out that cranberries also protect against cancer, particularly breast cancer, due in part to potent antioxidant polyphenols.
The fiber in cranberries is another big benefit, providing 20% of the daily recommended value in every serving for maintaining a flushed system. The same amount is found in manganese. One serving of cranberries also provides 24% of the daily value (DV) in vitamin C, along with vitamin E (alpha tocopherol), the only form of this powerful antioxidant actively maintained in the human body.
Fresh cranberries contain the most antioxidants; dried cranberries run a close second, but bottled cranberry juice contain the least. Make sure when buying juice or juice cocktails that it's 100% juice and not a "drink" which often (always) includes added sugar.
Because cranberries and cranberry juice contain oxalic acid and can also enhance the anticoagulant capacity of certain medications, individuals with urinary tract stones and those on warfarin therapy should limit their intake of these foods and beverages.
However, consume cranberries in moderation because they contain fructose, which may be harmful to your health in excessive amounts.