Echinacea - Scientific Background
Echinacea enhances the activities of immune cells.
Numerous laboratory studies have shown that echinacea extracts can stimulate generalized immune responses (Burger et al 1997; Bauer et al 1989).
Small studies with healthy human volunteers have not consistently shown specific immune responses, such as higher levels of white blood cells or greater activity of specialized white blood cells called phagocytes (Melchart et al 1995).
Echinacea does not appear to prevent upper respiratory infections.
Long-term use of echinacea does not ward off influenza or the common cold. A randomized placebo-controlled prevention trial among 108 persons with a history of frequent colds did not demonstrate a difference in the rate of occurrence or in the duration of new colds (Schoeneberger 1992).
Two subsequent trials also failed to find a preventive effect. In one study, 302 healthy volunteers were given echinacea extract or placebo for 12 weeks (Melchart et al 1998). In the other study, 109 patients with a history of more than three colds or respiratory infections in the preceding year were given echinacea extract or placebo for 8 weeks (Grimm and Müller 1999). In both studies, there was no advantage to taking echinacea extract.
Echinacea may reduce the severity and perhaps duration of some upper respiratory infections.
Taking echinacea soon after a cold or other respiratory flulike infection has started may reduce the severity of symptoms. Most of the randomized trials that used echinacea as a remedy were poorly designed (Melchart et al 1994).
However, the best of these studies found that taking echinacea extract on the first and second day after the infection started significantly reduced symptoms. In addition, two related placebo-controlled trials reported the beneficial effects of taking high doses of E. purpurea extract or E. pallida roots at the onset of a flulike or feverish infection. Echinacea appeared to reduce the severity of some symptoms (stuffy nose and headache) but not others (cough and swollen glands) (Braunig et al 1992; Braunig and Knick 1993).
A clinically significant effect of echinacea extract on cold symptoms was demonstrated in 246 healthy adult volunteers who caught a common cold (Brinkeborn et al 1999).