It's cranberry season!
Originally published on FoodNutritionScience.com.
One of North America’s native, commercially grown fruits, the cranberry is an American staple used ubiquitously in the Thanksgiving meal. Long praised for its tart taste and incredible versatility, the cranberry is also a proven natural healing agent. And while the cranberry is well known for it’s ability to promote urinary tract health, there is strong experimental evidence that cranberries have a favorable effect on blood pressure as well, along with a host of other promising health benefits, according to a recent article from an international group of nutrition scientists and published in the recent issue of Advances in Nutrition.
For the article, researchers looked at numerous studies on cranberry health, finding that the majority of recent clinical studies associate the cranberry’s potential health effects with the phytochemical content of the fruit. Cranberries are unique in that they are rich in A-type proanthocyanidins (PACs) – in contrast to the B-type PACs present in most other fruit. Why does this matter? Because A-type PACs work better than B-types to prevent E.coli bacteria from adhering to the urinary tract.
Additionally, cranberries are a rich source of other polyphenols, which have been associated with antibacterial, antiviral and anti-inflammatory properties. This anti-inflammatory property may be influencing the results in clinical studies that demonstrate the ability of cranberry products to lower LDL cholesterol and total cholesterol, and lower glycemic responses. Anthocyanins, known for their potential anti-oxidant properties, are another bioactive component present in high amounts in cranberries, contributing to their color and health benefits. A cranberry’s anythocyanin content increases as the fruit ripens.
Cranberries are rarely consumed raw, and more frequently appear at the Thanksgiving meal in a sweetened, cooked sauce. Dried cranberries and cranberry juice (again, both usually sweetened) are other popular ways to consume the fruit. While juice processing leads to some loss of phytochemicals through the elimination of the skin and seeds and thermal degradation, cranberry juice can contribute significantly to the intake of PACs and flavonols.
“The content of phytochemicals (bioactives) in all fruit, including cranberries, is typically reduced during harvesting, storage, and processing into a final product. Data are limited on this matter with regard to dried and cooked cranberries, though these products have been tested for total phytochemicals and antioxidant capacity; the results of these studies indicate the content of bioactives is still sufficient to achieve clinically meaningful results,” says lead study author Dr. Jeffrey Blumberg, professor of nutrition science and policy at Tufts University.
Cranberries may help protect against recurring urinary tract infections and thus reduce the need for prolonged antibiotic treatment. This has public health relevance given the global concern with drug resistance. The proposed mechanism for this benefit of the cranberry is the anti-adhesion action of its PACs, which appear to prevent E. colifrom binding to urinary tract walls – the primary culprit in urinary tract infections. There is also some evidence that cranberry bioactives may have a positive effect on gut bacteria, but this action has not yet been demonstrated in clinical trials.
Even with all this positive evidence, there are still gaps in the research. In fact, there are a number of studies finding inconsequential results on the relationship between cranberry consumption and health outcomes. One problem in all of these studies is getting the test subjects to comply with the test and consume consistently. Optimal doses have not been determined either.
“There are several excellent methods for determining most (albeit not all) of the principal flavonoids and other polyphenols in berry fruit. Several studies have determined the absorption (bioavailability) of these compounds into healthy human subjects. However, the clinical trials studying disease outcomes (such as UTIs) have not tested for these compounds in blood or urine, so it is not possible to determine from these studies whether the subjects were fully complying with the intervention and whether the blood/urine concentration achieved reached an efficacious level,” says Blumberg.
Still, the evidence, both regarding berry fruit in general and cranberries in particular, is encouraging. While certainly not conclusive, sufficient evidence is available now for professionals to promote increased consumption of berry fruit. Since part of the point of the 2010 Dietary Guidelines for Americans is to help consumers meet the recommended daily amount of micronutrients (from foods like fruits and vegetables), encouraging the increased consumption of fruit, including a berry fruit like the cranberry, could be a good way to increase our intake of bioactive compounds.
“While more research is warranted, I feel we know enough about their health benefits to continue to promote greater consumption of berry fruit, including cranberries,” says Blumberg.