Mention cranberry juice and “urinary tract infection” springs to mind. Most women and many men are familiar with the frequent urination and accompanying burning sensation that signals a bacterial invasion of the urinary tract. Today antibiotics solve the problem, but what did people do before? “Flushing the system” seemed a logical approach. All sorts of beverages were tried, but by the mid-1800s books on folkloric medicine were suggesting the use of cranberry juice. Based on anecdotal evidence, the juice developed a solid reputation for treating and preventing urinary tract infections.
Once bacteria had been identified as the cause of UTIs, scientists began to explore possible mechanisms by which cranberry juice could offer relief. Acidifying the urine to make it more inhospitable to bacteria was a possibility, as was the antibacterial action of hippuric acid, a component of cranberries. But trying to explain how cranberry juice worked before clearly demonstrating that it did was putting the cart before the horse. Finally, in 1994, Harvard researchers decided to mount a proper clinical study of the claims. They enrolled 153 older women, half of whom were given 10 ounces (285 millilitres) of cranberry juice every day, while the other half were given a look-alike drink containing no cranberry. The women who drank cranberry juice were 58 percent less likely to have levels of bacteria in their urine that would be expected to cause infections. As we would eventually learn, the effect was not due to acidity of the urine, nor to the antibacterial effect of hippuric acid. It had to do with compounds that prevented bacteria from adhering to the lining of the urinary tract.
Bacteria produce adhesives that enable them to stick to tissues so they can pick up nutrients more readily. These molecules fit into specific receptor sites on the epithelial cells that line the urinary tract. As was cleverly shown by Yale University researchers in 1994, compounds in cranberries block these receptors. Urine samples were collected from volunteers who were then given four ounces (115 millilitres) of cranberry juice to drink. Four to six hours later urine was again collected and incubated with E. coli bacteria, the kind that normally are responsible for urinary tract infections. The experiment was then repeated with eight ounces (230 millilitres) of juice. Separately, the scientists cultured cells taken from the lining of the human bladder and then mixed them with the urine samples. Lo and behold, the bacteria did not stick as effectively to the cells when the urine samples came from women who had consumed cranberry juice! Furthermore, the more juice consumed, the less the bacteria adhered to the cells.
Although the specific ingredients in the juice responsible for this effect have not been conclusively identified, speculation is that substances known as trimeric procyanidins may be responsible. Unfortunately, however, not every study has shown that cranberry juice acts favourably on UTIs. In some it worked no better than placebo. And there’s no question that in women with a history of UTIs, antibiotics (trimethoprim-sulfamethoxazole) prevent recurrence far better than cranberry juice. But of course with antibiotics there is the problem of resistance.
These procyanidins may do more than prevent urinary tract problems. Most ulcers are caused by infection with the Helicobacter pylori bacterium. Well, it seems that the procyanidins may also prevent these bacteria from infecting the stomach. Researchers in China chose a population with a high rate of Helicobacter infection, and in a placebo-controlled double-blind study, gave 97 people 500 millilitres (just over two cups) of cranberry juice for 90 days, while 92 others got a placebo. They found that H. pylori was eradicated in 14 people in the cranberry group but in only five in the placebo group. Not an earth-shaking difference, but significant nevertheless, especially given the resistance issues we are now encountering with antibiotics.