The tart fruit holds promise for preventing kidney stones, stomach ulcers, gum disease and atherosclerosis.
Scientists are getting serious about studying the lowly cranberry. The National Institutes of Health is underwriting research to find out exactly how effective it is in preventing urinary tract infections. But the applications for cranberries don?t stop there. This antioxidant-packed berry may also help prevent kidney stones, stomach ulcers, gum disease, atherosclerosis and cancer.
Urinary tract health
According to NIH, every year urinary tract infections send 7 million Americans to their doctors and another million to emergency rooms. One hundred thousand people end up being hospitalized. There?s no doubt UTIs are a major source of suffering and medical expense. To combat the all-too-common condition, many people turn to cranberry.
This folk remedy has been used for a long time, but researchers have only scrutinized its effectiveness in the last 10 years. In 1994, the Journal of the American Medical Association published a study with results showing that women who drink cranberry juice cocktail slash their risk of having a urinary tract infection by 42 percent.1 Results of other recent studies show drinking cranberry juice or taking cranberry tablets daily cuts the rate of UTI recurrence in women by one-third to one-half.2,3 In one of these studies, researchers found cranberry tablets to be a more cost-effective way to prevent UTIs than drinking juice or juice drinks.
The rationale for this interest in the tart little fruit has been that cranberry creates an inhospitable environment for bacteria in the urinary tract by acidifying the urine. But another mechanism is thought to be even more important in protecting against UTIs. Most UTIs are caused by E. coli, which normally inhabit the intestinal tract. To propagate in the urinary tract, these bacteria must be able to attach to the walls of the tract. They do this by forming fibers on their cell walls called fimbrials. The fimbrials make an adhesive that sticks to receptors on the surfaces of urinary tract cells. In the laboratory, cranberry extract has been shown to irreversibly inhibit the ability of bacteria to make these fibers on their cell walls. Without the ability to adhere to human cells in the urinary tract, bacteria are harmlessly flushed out of the system in the urine.6,7
Kidney stones are another common urinary tract problem. Most kidney stones are composed of calcium oxalate; cranberry is high in oxalic acid. The jury is still out on how cranberry may influence kidney stone development because research on cranberry?s effect on urinary oxalate levels has produced contradictory results. In one recent study, a researcher found the oxalate content of urine increases 43 percent in people taking cranberry supplements. As a result, the scientist who conducted this study warns cranberry tablets are contraindicated in people with a history of kidney stones.8
On the other hand, another researcher found drinking cranberry juice reduces some risk factors for oxalate kidney stone formation.9 In this crossover study, people who drank cranberry juice excreted less oxalate and phosphates and more citrate than those who drank water, which would be expected to decrease their risk of forming stones. The cranberry drinkers also showed less supersaturation of calcium oxalate, which means the calcium oxalate was dissolved in the urine rather than precipitating into a solid that could form a stone.
Other researchers have speculated that because cranberry acidifies the urine, it could help prevent stones formed from two other substances, brushite and struvite.10 (Brushite is a calcium-phosphate mineral complex. Struvite is a magnesium-ammonium-phosphate complex made from the urea produced by bacteria during a kidney infection.) Because scientists currently disagree, it will take additional research to answer the question of how cranberry influences kidney stone formation.
Adhesion of bacteria to human body cells is the first step in most bacterial infections, not just UTIs. Therefore, scientists are beginning to explore whether cranberry juice?s anti-adhesive ability can be used to protect against other types of bacterial infection, including stomach ulcers and gum disease. The bacteria Helicobacter pylori causes most stomach ulcers. In an Israeli study, researchers found that in the laboratory cranberry prevents H. pylori bacteria from sticking to stomach mucus.11 Cranberry may also guard against the oral bacteria that cause cavities and periodontal disease. In the laboratory, cranberry has been found to inhibit the formation of bacterial complexes that cause dental plaque, and also to kill anaerobic bacteria, which cause the most severe gum problems.12 As bacterial resistance to antibiotics rises, it is critical to find new ways to halt bacteria without increasing resistance. Cranberry may fit the bill. Since it does not kill bacteria, it is unlikely to contribute to the development of resistant strains.13
Cranberry contains high levels of several powerful antioxidants.14 In fact, cranberries have the loftiest phenol levels of any fruit, distantly followed by red grapes.15 Cranberry is also a potent source of flavonols. Some of the specific anthocyanidins in cranberry have antioxidant strength equal to or greater than vitamin E.16 Resveratrol, believed to be partially responsible for the health benefits of red wine, also is present in cranberries.17 With all of this antioxidant firepower, it is no surprise that a 2002 study found that cranberries had the strongest antioxidant capacity of 11 tested fruits,18 and that cranberry juice increases plasma vitamin C levels. 19
Antioxidant flavonols extracted from cranberries have been found to block several steps in atherosclerosis development. First, flavonols prevent oxidation of low-density lipoprotein cholesterol. They also prevent platelets, or clotting cells, from sticking together; relax blood vessels; and inhibit the immune system?s inflammatory response—all strategies that protect hearts and blood vessels.20
Cranberries may also protect against cancer. In one preliminary study, anthocyanidin extracts of cranberry fruit showed potent antitumor activity in laboratory screening tests.— Since then, researchers have purified and identified a previously unknown substance in cranberry that has potent effects against breast, prostate and cervical cancer cells.22 However, studies on animals and humans have not yet been conducted.
Cranberry research is still in its infancy, but every day new discoveries are expanding our appreciation for the little berries? uniquely powerful and healing compounds. It is not unrealistic to expect that in the future we will consider cranberry a potent natural medicine.
Marilyn Sterling is a free-lance writer and consultant in Trinidad, Calif.
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19. Pedersen CB, et al. Effects of blueberry and cranberry juice consumption on the plasma antioxidant capacity of healthy female volunteers. Eur J Clin Nutr 2000;54(5):405-8.
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22. Murphy BT. Identification of triterpene hydroxycinnamates with in vitro antitumor activity from whole cranberry fruit (Vaccinium macrocarpon). J Agric Food Chem 2003;51(12):3541-5.
Natural Foods Merchandiser volume XXV/number 3/p. 118-119