Cranberries provide a healthy dose of vitamin C and other antioxidants but they're mostly associated with being helpful in treating UTIs.
Urinary tract infection (UTI) is no fun and it’s been suggested that cranberries may help to both prevent and treat it. A good deal of research has been conducted on this but with uncertain results, yet there’s a wealth of expensive marketing and clever ads so it’s hard to know what to believe.
Cranberries contain natural compounds called proanthocyanidins that can prevent bacteria from sticking to the bladder wall. This may be helpful in the prevention and treatment of UTIs but most supplements and juices don’t contain enough to be effective. Also, many cranberry juices are very diluted and extremely sweet so are unlikely to help at all.
Supplements usually contain cranberry powder, which is made either from dried juice or the dried skins left over from the juicing process. Supplements made from juice are far superior to those made from cranberry skins but it's hard to tell which is which. Some manufacturers state how much of the active proanthocyanidins the supplement contains and based on research, you need at least 36 milligrams per day to help prevent UTIs.
Studies on the efficacy of cranberry supplements and juices provide conflicting information – some show there’s no effect while others show they may help a little. The bottom line is that cranberries are not a cure for UTIs but might be beneficial for prevention if you take a high enough dose.