Nature's Pharmacopeia: A World of Medicinal Plants
The North American cranberry is a perennial evergreen vine adapted to grow in the wetlands of New England, the eastern maritime Canadian regions, and the northern Great Lakes area. The cranberry plant thrives in moist soil rich in organic material, where it creeps low to the ground, producing small, glossy, oval green leaves and bright-red fruits in late autumn.2 The genus Vaccinium includes numerous small-fruited species mostly growing in the north temperate zone of the globe, including the American and Eurasian small cranberry (V. oxycoccos), Eurasian lingonberry (V. vitis-idaea), and North American blueberry (V. corymbosum).3 Cranberry fruits have long been employed for their nutritive and medicinal properties (figure 14.1).
Among the indigenous North Americans, cranberry was a trade good and foodstuff eaten fresh or preserved by drying. Crushed berries were an ingredient in the American Indian food called pemmican, a mixture of cranberry, animal fat, and dried meat that kept well and provided a stable reserve of energy during lean times.4 The first Europeans to tread the northern reaches of the New World may not have recognized the American cranberry as a relative of the smaller-fruited variety (V. oxycoccos) back home, but the latter was well known to botanists, who considered its juice useful against fevers and illnesses caused by the humor yellow bile.5
Early American accounts of cranberry demonstrate its culinary and medical roles, sometimes inspired by observations of indigenous American uses. For example, Roger Williams (ca. 1603–1683), the founder of New England’s Providence Plantation, was introduced to cranberry by the Narragansetts and described it in 1643 as “another sharp, cooling Fruit growing in fresh Waters all the Winter, Excellent in conserve against Feavers.” He also noted that they used cranberry and grain to “make a delicate dish which they cal Sautáuthig; which is as sweet to them as plum or spice cake to the English.”6 Later, in 1672, the English traveler John Josselyn (1608–1675) remarked on cranberry’s place in cuisine, writing that “the Indians and English use them much, boyling them with Sugar for Sauce to eat with their Meat.” European explorers certainly experienced the effects of scurvy (now recognized as vitamin C deficiency) from a lack of fresh fruits and vegetables, and Josselyn noted its usefulness against that scourge as well as the “the fervour of hot Diseases.”7 Other early health-related applications of cranberry include the treatment of wounds, stomach concerns, liver problems, and infections.8
Figure 14.1 Cranberries: (left) fruit; (right) harvest. ([right] Photograph by Keith Weller; U.S. Department of Agriculture, K4418-6)
Cranberry became cultivated widely in North America during the nineteenth and twentieth centuries and is now marketed in several forms: as whole fruit, as prepared sauces, as juice, and in extracts in the form of powders or capsules. Cranberry is tart because of the presence of acidic and astringent chemicals, and it possesses several types of complex polyphenolic compounds, a mixture of substances that might account for its ascribed health-related properties.9 Certainly, the effectiveness of cranberry against scurvy can be explained by its vitamin C (ascorbic acid) content.10 Cranberry also contains numerous compounds with antioxidant properties in addition to vitamin C.11 Much current interest in cranberry is focused on its possible utility in preventing or treating urinary tract infections. Such infections result from the colonization of the urethra or bladder by bacteria such as the pathogenic strains of Escherichia coli.12
Although the mechanisms of cranberry’s possible antibacterial properties have yet to be thoroughly defined, there seems to be a role for a particular form of polyphenolic compound called an A-type proanthocyanidin (figure 14.2).13 In laboratory tests, these chemicals, which comprise a portion of a complex mixture, have been demonstrated to inhibit the adhesion of E. coli and other pathogenic bacteria to the type of epithelial cells that line the urinary tract.14 Yet the extension of this laboratory finding to human health has been troubled by challenges of physiology and experimental design. For the former concern, investigators question whether the complex compounds present in cranberry juice or extract are absorbed from the human digestive system and distributed efficiently. That is, if the A-type proanthocyanidins and related compounds are not taken up into the bloodstream from the intestine or are chemically broken down in the body, it is difficult to imagine their accumulation in the urine. Therefore, any extension of test tube or Petri dish findings to the whole organism would demand a better understanding of the metabolism of cranberry’s constituents.15 As to the matter of experimental design, recent studies of cranberry use in human populations have employed a suite of dissimilar scientific protocols and have tested commercial and proprietary cranberry extracts in multiple forms, material not standardized to a common set of criteria.16It is therefore difficult to ascertain in such human studies whether cranberry or any of its possible active principles may play a role in preventing or treating urinary tract infections.
FIGURE 14.2 A-type proanthocyanidins are speculated to interfere with bacterial adhesion to the cells lining the urinary tract.
Mixtures of chemicals prepared from an herbal source in which the concentration of particular molecules of interest has been determined using appropriate laboratory techniques
To date, there is little evidence supporting the use of cranberry to prevent urinary tract infections, nor have there been many recent studies on the effectiveness of cranberry to treat existing infections.17 Yet the laboratory findings showing that certain cranberry constituents interfere with bacterial pathogenesis suggest that the fruit could yield useful medicinal products with demonstrable clinical activity in the future.