There is evidence that if you take a glass of cranberry juice a day, it could reduce urinary tract infections (UTI). Cranberry extract is also available in powder form. A study was conducted at the Finnish Student Health Services at Oulu University with 150 women with persistent UTIs. Fifty drank just under 2oz of cranberry juice concentrate per day for six months. Another 50 drank a preparation of Lactobacillus, while the final 50 women were given no treatment. After six months, only eight women taking cranberry juice had experienced a UTI, compared with 19 of those taking Lactobacillus, and 18 not taking anything.
50 milliliters of cranberry juice concentrate seems to be well tolerated and is effective for preventing bladder infections. Larger quantities should be considered when an infection is present. Cranberry cocktail or juice may be very diluted and may produce no benefit if not taken in sufficient quantities to approximate a 50ml (just under 2 ounce) dose of concentrate. Check labels to ensure a high proportion of actual cranberry juice in whatever preparation you choose, or use only concentrate or powder forms.
A single dose of cranberry juice (330ml) decreased urinary pH and increased excretion of oxalic acid in a multi-phase, placebo-controlled study of 12 healthy men. [Eur J Clin Nutr 2002;56(10): pp.1020-1023] Other types of juices tested, such as blackcurrant and plum, did not have the same effect.