Zinc and the Common Cold: dose matters

Jacob Schor ND, FABNO

September 24, 2012

www.DenverNaturopathic.com

 

Oral zinc lozenges help reduce intensity and duration of the common cold but only if you take large enough doses of the right chemical form.

 

At this time each year we stock our clinic shelf with cold and flu remedies to get ready for the winter ahead.  This is also a good time to review new studies published in the medical literature that support the use of these supplements. Let’s start with zinc lozenges.  These are rather curious; no one really understands why they work.

 

The first anyone heard of using zinc to treat the common cold was the publication of a double-blind study by George Eby and colleagues in January 1984.    The idea that zinc lozenges dissolved in the mouth would be useful for treating the common cold started from a ‘serendipitous observation’ that a cold of a 3-year-old girl with leukemia disappeared quickly when she dissolved a zinc tablet in her mouth instead of swallowing it. 

 

Since that first report at least 15 other additional clinical trials have been published.  Zinc worked great in some and not at all in others, a situation that left many of us wondering. 

 

Two papers published last year put the matter to rest.

 

A February 2011 Cochrane Database Review, considered the gold standard in these sorts of reviews, combined data from thirteen clinical trials and two preventive trials.  The conclusion: zinc intake is associated with a reduction in duration and severity of common cold symptoms.

 

In May 2011, Finnish scientist, Harri Hemlä, sorted this out further in an article published in The Open Respiratory Medicine Journal.  He collected and analyzed the data from the same thirteen placebo-controlled studies.  It turned out dose matters: five of the trials used a daily zinc dose of less than 75 mg.  None of those studies showed any benefit.  Three trials used zinc acetate in doses over 75 mg and their combined results found a 42% reduction in the duration of the colds.  Five trials used other chemical forms of zinc over 75 mg and they produced only a 20% reduction in the duration of colds. 

 

Thus Hemlä’s suggestion, take zinc acetate in big doses, more than 75 mg/day to treat the common cold.

 

There’s another problem with using zinc.  We don’t know why it works. Zinc certainly improves immune function over time but the apparent improvement in cold symptoms occurs too rapidly for this to be the explanation.  As Hemlä writes:

“…the fundamental questions in evaluating a potential treatment should be efficacy, safety and cost whereas biological explanations and the effects on surrogate outcomes should be secondary issues.”

 

In other words, if it works, do we care if we don’t know why?

 

Probably not, but perhaps the most interesting theory put forth to explain zinc’s action comes from George Eby, who conducted the first clinical trial 28 years ago.  He’s had a long time to think about this.  His theory is complicated and involves zinc acting on a biological closed electric circuit that transfers low voltage current between the nose and mouth. [4]  I won’t attempt to explain it here but his explanation, published last June, is at: http://www.expert-reviews.com/doi/pdf/10.1586/ers.12.17

 

 

References:

 

1. Eby GA, Davis DR, Halcomb WW. Reduction in duration of common colds by zinc gluconate lozenges in a double-blind study.

Antimicrob Agents Chemother. 1984 Jan;25(1):20-4.

 

2. Singh M, Das RR. Zinc for the common cold. Cochrane Database Syst Rev. 2011 Feb 16;(2):CD001364.

 

3. Hemilä H. Zinc lozenges may shorten the duration of colds: a systematic review. Open Respir Med J. 2011;5:51-8. Epub 2011 Jun 23.

 

4. Eby G. The mouth-nose biologically closed electric circuit in zinc lozenge therapy of common colds as explanation of rapid therapeutic action. Expert Rev Respir Med. 2012 Jun;6(3):251-2.

 

Eby GA, Davis DR, Halcomb WW. Reduction in duration of common colds by zinc gluconate lozenges in a double-blind study.

Antimicrob Agents Chemother. 1984 Jan;25(1):20-4.

 

Singh M, Das RR. Zinc for the common cold. Cochrane Database Syst Rev. 2011 Feb 16;(2):CD001364.

 

Hemilä H. Zinc lozenges may shorten the duration of colds: a systematic review. Open Respir Med J. 2011;5:51-8. Epub 2011 Jun 23.

 

Eby G. The mouth-nose biologically closed electric circuit in zinc lozenge therapy of common colds as explanation of rapid therapeutic action. Expert Rev Respir Med. 2012 Jun;6(3):251-2.