DOES ZINC STOP THE COMMON COLD?
Can Zinc Treat the Common Cold?
By Ben Lomaestro, from Medscape Pharmacists
Question: Is zinc effective for treatment and prevention of the common cold?
Response from Ben Lomaestro, PharmD, Senior Clinical Pharmacy Specialist in Infectious Diseases, Albany Medical Center Hospital, Albany, New York:
The common cold is one of the most widespread illnesses, with adults averaging 2-4 episodes per year. Morbidity associated with the common cold is not trivial. The median duration of illness is 7.4 days, with 25% of cases lasting approximately 2 weeks.
Although the exact mechanism of zinc treatment for the common cold is unknown, ionized zinc is thought to assist T cells which kill virus-infected cells. Ionized zinc may act by inhibiting the formation of viral capsid proteins and/or by stabilizing and protecting cell membranes.
The majority of viral replication occurs within 1 day of symptom onset, and this is the time interval for which intervention might be most beneficial, although administration within 3 days may still have benefit.
A recent Cochrane review evaluated 13 therapeutic trials (966 patients) and 2 preventive trials (394 patients).
Common cold duration was reduced if zinc was taken within the first 24 hours of cold symptom onset. Illness severity was also reduced.
Another recent systematic review of 13 clinical trials evaluating zinc lozenges found similar benefit. The author hypothesized that substantial variation in study outcomes was the result of differences in the 7-fold variation in the total daily zinc dosage.
Five of the studies reviewed used < 75 mg/day of zinc and none found a beneficial effect, whereas 7 of 8 comparisons using > 75 mg/day of zinc found statistical benefit.
The author estimated that lozenges containing 75 mg/day or more of zinc could reduce the duration of colds by 32% and possibly more with zinc acetate formulations.
Eby reviewed 15 randomized controlled trials of zinc lozenges and found efficacy to strongly correlate with ionized zinc content at physiologic concentration in a dose-response manner.
Best results were achieved with lozenges having only 1 ligand (acetate or gluconate) and consequent high ionic zinc content.
A lozenge with the same dose of zinc as another may have a different level of free zinc if it contains substances that bind zinc ions tightly, such as citrate, tartrate, or glycine. Products that do not release ionic zinc may, in fact, make colds worse.
Zinc ions may also be partially inactivated due to complex formation by components of saliva.
Contact time is also important. Lozenges are thought to be most efficacious when dissolved slowly in the mouth over 20-30 minutes, releasing > 18 mg of zinc and administered every 2 hours.
The Cochrane review also found a favorable prophylactic effect of zinc administration upon the incidence of colds. The incidence rate ratio of developing a cold was less in the zinc group.
Zinc supplementation in children resulted in fewer absentee days from school .
Dr. Pinna says:
There are many conflicting opinions about the use of zinc to reduce the severity of the common cold. For example, the Australian government has reviewed all studies and concludes: “We don’t know.â€
I feel that the use of zinc lozenges for three days is relatively safe and may be beneficial. The cost is low. I tell patients: “Try it for three days. Start immediately. Any bad effects: Stop! Throw the lozenges away!
I have had mixed results. Some patients swear by zinc. Others had no relief.
The major problem is the number of viruses that cause the symptoms. We never know which one is the culprit. If you are lucky you may hit that virus which is susceptible to zinc.
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