We all know that fruit juice is generally good for you. But every day it seems scientists are discovering new benefits for specific illnesses. Yesterday, U.S. researchers revealed that beetroot juice can help keep dementia at bay, as it contains nitrate, which helps open blood vessels, boosting blood supply to the brain... Cranberry juice for urinary infections -- How it works: A study conducted this year showed that cranberry juice prevents the growth of the bacteria E.Coli, the most common cause of urinary infections. Researchers who presented their findings to the American Chemical Society showed that within eight hours of drinking a glass of cranberry juice, the juice could help prevent bacteria from developing into an infection in the urinary tract. However, contrary to popular belief, the juice will not treat cystitis if the infection has already occurred — indeed, because it is acidic it can actually exacerbate the discomfort.