Thus far, there has been inconclusive evidence to support
the use of vitamin C and extracts of the plant Echinacea in
common cold prevention. Daily supplementation with large
doses of vitamin C does not seem to prevent common colds;
however, there seems to be a modest (8– 9%) reduction in
the number of symptom days in individuals with established
cold symptoms, with larger doses having a greater effect
[83]. For Echinacea, currently available data from studies
conducted in the adult population show positive findings
both in the treatment and prevention of upper respiratory
infection. However, variations in the design of the clinical
trial and in Echinacea preparations have to be taken into
account [84].
Zinc has been shown to possess antiviral properties in
vitro, and different preparations of zinc have been proposed
for the treatment of the common cold. Zinc lozenges
appeared to have positive effects on adults, but negative
effects on children in terms of duration and severity of
common cold symptoms [85,86]. Zinc nasal spray appears
to reduce the total symptom score but has no effect on the
duration of the common cold [87]. Recent research shows
that zinc nasal gel can reduce the median time to cold
resolution compared to placebo (4.3 days vs. 6.0 days;
p = 0.02) and decrease the median time to resolution of nasal
congestion, nasal drainage, hoarseness and sore throat [