Echinacea, a medicinal herb that came to prominence thanks to its use by Sioux Indians, can more than halve the risk of catching a cold, a wide-scale study has confirmed. Taking echinacea supplements can reduce the risk of a cold by 58 percent and may also shorten the duration of a cold almost one and haf days, according to the paper, published on Sunday in the July issue of the journal The Lancet Infectious Diseases.