COLDS
AND FLU: WHAT WORKS?
By
Maryann Napoli
We
took this question to the Cochrane Library and found positive
results for high doses of vitamin C, the herbal remedy called
Echinacea, and enough evidence to suggest that zinc lozenges
merit more research. The Cochrane Collaboration (CC) is
an international network of experts from different fields
who examine the quality of medical research to help consumers
determine which treatments have scientific evidence of efficacy.
Vitamin C
The CC reviewed 30 trials; most of them tested both the
preventive effect of maintenance doses (10-30 mg/daily)
of vitamin C as well as the therapeutic effect of taking
high doses once a cold developed. In all of the trials,
adults and children had been randomly assigned to take vitamin
C or a placebo. Though the combined results of these trials
showed no preventive benefit to vitamin C, the CC reviewers
did find an exception. People who were malnourished and/or
under heavy physical stress did, in fact, had a lower number
of colds taking maintenance daily doses of C.
As for stopping a cold once it appeared, the CC reviewers
found a "clear effect on the duration of symptoms"
in people who began taking high doses of vitamin C at the
first sign of a cold, as well as a reduction in severity.
This finding was judged "modest but certainly not trivial."
The study participants began taking incremental doses of
vitamin C in the 1-3 gram range, which would not be considered
high enough by the late Linus Pauling, the leading proponent
of this treatment. In a 1987 interview, Dr. Pauling told
this reporter that people should begin taking vitamin C
at the first sign of a cold and continue taking it to their
level of tolerance. To Dr. Pauling, high doses will eventually
reach the realm of 20 grams for adults. (In its powdered
form, vitamin C is measured in grams, rather than milligrams.)
The level of tolerance differs from person to person, but
Dr. Pauling said it is reached once diarrhea begins.
The CC reviewers left the door open for the possibility
that the doses were not high enough in these trials, concluding
"dose response clearly requires further research...incremental
doses as high as 8 grams daily may heighten the therapeutic
effect."
Echinacea
Echinacea is an herb believed to be an immune stimulant.
The CC located 16 clinical trials in which people with colds
had been given either this herb or a placebo. Half the trials
looked at preventing colds, and the other half looked at
treatment. The CC found that the majority of the trials
reported positive results for both prevention and treatment.
There was not enough evidence to recommend a specific Echinacea
product, however. Echinacea is sold in a variety of forms,
ranging from powdered root to tinctures. Many of the trials
assessed by the CC combined Echinacea with vitamin C or
other herbs. In Germany alone, the CC found that there are
200 different Echinacea products on the market.
Zinc
Zinc lozenges have been pitted against placebos in seven
clinical trials. Though the CC found the results to be inconclusive,
zinc showed enough potential to indicate that further research
is warranted.
Antibiotics
Many consumers and doctors think that antibiotics are appropriate
treatment for a cold because they will prevent the development
of a bacterial infection. The CC found nine clinical trials
with the combined total of 2,157 participants who range
in age from two months to 79 years. All of the participants
had been randomly assigned to take antibiotics or a placebo
once a cold had been diagnosed. No benefit was found for
antibiotics and they were associated with a significant
increase in adverse effects, such as rash, vomiting, and
diarrhea.
For More Information:
Access to the Cochrane Library is on a subscription-only
basis, but the abstracts or summaries of the reviews are
freely available at www.cochraneconsumer.com.
--
Maryann
Napoli is the associate director of the Center for Medical
Consumers in New York City.
October 2003
