30 — Zinc for the treatment of the common cold: a systematic review and meta-analysis of randomized controlled trials

This has been a long-standing discussion in my family: Does taking a zinc supplement — perhaps Cold-Eze — shorten the duration of a cold?

There are two parts to this question: Namely, ① Does zinc reduce rhinovirus reproduction? and ② Do zinc supplements reduce the duration of the common cold?

I separate these two questions because it’s pretty common for a homeopathic “treatment” to contain an ingredient that seems conspicuously useful; but, much like how salt contains chlorine and doesn’t kill us, I wonder how many of these homeopathic “rememdies” are really just bad science resting on the laurels of others’ legitimate research.

To answer the first question, we can look to rhinovirus research: At a cellular level, the presence of zinc does seem to reduce the reproductive rate of the virus. Answering the second question is trickier.

This review covers 17 trials from the literature, spanning 2121 participants total. The short answer to this question is the adult zinc population had shorter colds by about a day and a half, and the children subgroup exhibited “no significant effect”.

The symptoms, at least during the cold, seemed unaffected by the zinc supplements. And although the paper found that “orally administered zinc shortened the duration of cold symptoms”, the authors point out that there is poor dataset homogeneity and poor quality of evidence, and this leaves the question still very much on the table.

Oh BY THE WAY there is some very juicy drama currently unfolding between two authors of two different reviews; Harri Hemila, citing “numerous…problems” in Das’s review, and Rashmi Das, flinging some of “it is really sad to see that Harri is trying to disseminate his personal opinion.” Anyway, this is the retraction notification’s comments section which I assume means that there aren’t too many more reviews on this topic forthcoming for a while.