Traditionally, the Native Americans used Echinacea for everything from colds and sore throats, to snake bites and general infections. The Eclectic physicians in the late 1800s used Echinacea as a blood purifer, local antiseptic and anaesthetic, and internal treatment for infections and ulcers. Echinacea was introduced to Europe in the 19th Century, and has been studied there since the 1950s in laboratory and clinical trials. The trials have centred on Echinacea's effect on the non-specific immune capabilities in dealing with a number of infections, particularly colds and flu.

Clinical Studies

Along with the other two commercially available species, E. purpurea has been put to the test in a number of clinical trials. There have been at least 40 studies of Echinacea's effectiveness in either reducing the occurrence of URTIs, or reducing severity and/or duration of the infections. Melchart et al reviewed the methodologies used in the 40 studies and selected 16 studies involving 3,396 patients for further analysis of the treatment and the outcomes1. Eight of the studies were prevention trials comparing Echinacea with placebo (5 trials) or no treatment (3 trials) - four of the trials against placebo control were between 8 to 12 weeks in length. The remaining 8 studies were treatment trials lasting between 6 and 10 days, and the researchers studied the duration of infections and the severity of symptoms.

The review showed that the majority of the studies reported positive outcomes, and overall the results suggested that Echinacea preparations may be effective in both the prevention and the treatment of common cold infections. The reviewers noted the variety of preparations used, making it hard to make one-on-one comparisons. They also concede it is not easy to clinically assess the common cold. In clinical studies patients were given a continuous dosage level. In practice however, consumers who self-treat colds start taking Echinacea at the first sign of symptoms, before the cold reaches its maximum, and the dosage tends to be high in the beginning, tapering off after one or two days.

The review of clinical trials found:l

Treatment at the earliest onset of symptoms is associated with the maximum benefit.
Echinacea is associated with a 15 - 20% reduction in the risk of occurrence of a cold.
The US National Institutes of Health have given a grant to the University of Washington to study the effectiveness of Echinacea in treating URTIs in children. The two-year study starts this year and will involve 600 children between the ages of 2 - 11, and will compare Echinacea with a placebo

Mode of Action

The exact mode of action of Echinacea is not clearly defined, although it is obviously due to the activity of a number of different components.

These components can be divided into three classes:

Polysaccharides
Caffeic acid derivatives
Alkylamides and polyacetylenes
The polysaccharides occur at higher levels in the juice of E. purpurea and dried juice preparations are standardised on levels of fructofuranoside polysaccharides. These preparations have been shown to have a potent immune stimulating ability on cytokine production in normal human blood macrophages.2

In another study E. purpurea juice was shown to have interferon-like activity against the flu virus. 3

The major caffeic acid derivate in E. purpurea is cichoric acid which has been shown to stimulate phagocytosis in vitro - phagocytosis is a major factor in the body's nonspecific immune response.

The alkylamides are responsible for the characteristic tingling in the mouth of E. purpurea preparations. Polyacetylene compounds have been shown to inhibit the growth of bacteria, including Streptococci,3 which may explain the effectiveness of Echinacea in throat infections.

To summarise, it seems then that the mechanism of action of Echinacea is the stimulation of the body's nonspecific immune defence capacities,1 and the total immune stimulatory activity is due to combined action of several constituents, especially the three outlined above. Echinacea preparations may be standardised on one or a combination of the three components: fructofuranosides, cichoric acid and alkylamides.

Dosage and Treatment Duration

Echinacea is usually administered 2 to 3 times daily. The ideal period of treatment is not fixed; in European clinics Echinacea is sometimes given for alternating periods of three days on and three days off. 4 There doesn't appear to be any evidence for suggestions that prolonged use of Echinacea can deplete the immune system. In the clinical studies of Echinacea's efficacy for either prevention or treatment of colds, the longest study period (for prevention) was 12 weeks. One study actually showed that the immune response was considerably greater after 10 weeks of continuous dosing than after 2 weeks, suggesting an enhancement of immune function with continuous use.5

Nevertheless a sensible recommendation is to conform with the advice of the European Commission E monograph for Echinacea, 6 which suggests that preparations be used for up to 8 weeks.

Echinacea Preparations

Echinacea is available in a number of presentations and dosages. Liquid extracts have higher levels of cichoric acid and alkylamides, and have a localised effect on sore throats when swallowed. The dosage can be varied for prolonged use to reduce the risk of catching cold, or increased at the first sign of symptoms. Liquids are suitable for children, as the dosage can be adjusted according to age and diluted with juice to ensure compliance.

The dried juice contains potent polysaccharides and is used in maximum strength tablets to reduce the severity and duration of colds and flu at the first sign of infection. Echinacea lozenges help reduce the symptoms of colds, but also have a soothing localised effect on some throats, and may help reduce the symptoms of nasal congestion and catarrh.

Summary

Echinacea purpurea

Is the most widely studied Echinacea species
Contains the active ingredients fructofuranosides, cichoric acid and alkylamides
Stimulates the nonspecific immune system
Reduces the frequency of cold
Reduces the duration of colds
Reduces the severity of cold symptoms
Has a localised effect on sore throats
Is more effective when given 3 times daily
For adults the effective dose equivalent to dried herb (or fresh herb for juice preparations) is

500mg three times daily for prevention
1000mg three times daily for treatment