Herbal remedies continue to grow in popularity in the U.S. as demonstrated by expanding sales with seemingly no correlation to scientific research. Echinacea preparations have developed into the best-selling herbal immunostimulants (Bauer, 1998). Nine species of the genus Echinacea are found today in the U.S. and Canada (McGregor, 1968). Native Americans used Echinacea to treat wounds, snakebites and other animal bites, tonsillitis, headache, and cold symptoms (Hobbs, 1989). In the early 1900s in the U.S., Echinacea was the most utilized indigenous medicinal plant. After the introduction of antibiotics, its use declined in the U.S., although today it remains popular in Europe (Foster, 1991).
Although Echinacea is processed and sold around the world, Switzerland and Germany have been in the forefront by marketing more than 800 homeopathic products and drugs containing Echinacea (Brevoort, 1996). Analyses of these preparations have shown that three different species of Echinacea are used in medicine and homeopathy: Echinacea angustifolia DC, Echinacea pallida (Nutt.) Nutt., and Echinacea purpurea (L.) Moench. (Asteraceae) (Bauer, 1998). Even though a number of species of Echinacea have shown an immunostimulating effect, E. purpurea has been the type most often used for relief of symptoms of flu, cold, and upper respiratory illnesses (Melchart et al., 1995; Burger et al., 1997). When the aqueous extracts of the aerial parts of the E. purpurea were subjected to systematic fractionation and pharmacological testing, the result was the isolation of two polysaccharides with immunostimulating properties (Wagner and Proksch, 1981). These polysaccharides were found both to stimulate phagocystosis in vitro and in vivo, and to augment the production of oxygen radicals by macrophages in a dose-dependent manner (Stimpel et al., 1984). Problems with analyses of these components continue since the methods are still evolving (Bauer, 1998). Polysaccharides in Echinacea are analyzed through specific determination by isolation and structure elucidation or by nonspecific determination by hydrolysis of monosaccharides; neither of these methods is yet commercially obtainable (Bauer, 1998). E. angustifolia (a component of Echinacea Plus®) has also been shown, when combined with other types of Echinacea, to have an immunostimulating effect in relieving cold and flu symptoms (Melchart et al., 1995).
Researchers have studied various time intervals for Echinacea in the prevention and treatment of cold and flu symptoms. Some differences have been determined in research findings on the efficacy of Echinacea as a prophylactic over time. In a 6-month double-blind placebo study, the Echinacea treatment group had fewer respiratory reinfections (19% vs. 32%), an increase in time interval between such reinfections (25 vs. 40 days), a reduction in the average length of colds (5.3 vs. 7.5 days), and less severe symptoms (Schoneberger, 1992). Grimm and Müller (1999), however, found that Echinacea taken prophylactically during a 3-month period did not significantly decrease
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