Zinc Supplements for the Common Cold?

Goal: To introduce and explore zinc lozenges as an effective treatment for the common cold.

Motivation: There has been many studies over the past several decades searching (and finding) a link between zinc lozenges and the length of a rhinovirus infection (the common cold). Some studies said that zinc can reduce the length of a cold, others didn’t find any definitive correlation. Recently, meta-analysis of previous studies and exploration of potential mechanisms have emerged and give evidence that Zinc is actually very effective at battling the common cold. I feel that this brings the use of zinc to combat the common cold out of the homeopathic medicine category and into mainstream science and should therefore be considered as a treatment for the masses.

Executive Summary: Yes. It seems that zinc gluconate, something like the very popular Cold-Eeze, if taken early enough against rhinovirus colds can significantly reduce the time it takes to fully recover.

Reasoning:
What is Zinc? Zinc is a metal, but like all metals, there are different forms in which it can be in. Zinc can be a lone charged ion in solution, it can be bound by some other molecule, or it can be in a crystalline solid. It turns out that the Zinc ion (iZn) is the form of Zinc in solution is what demonstrates anti-cold effects. This is partly why previous studies may have given different and opposite conclusions on Zinc’s effectiveness as a treatment. Lozenges, depending on their composition, may release inadequate amounts of Zinc ions to have an effect on the rhinovirus when at physiological pH. (1) One type of Zinc that showed a benefit in studies is zinc gluconate, it releases about 72% of iZn when taken. Zinc Acetate is another form which releases near 100% iZn when taken.

What does Zinc do?
Sure, zinc has been shown in many studies to reduce the length of the common cold, but how does it do this? It’s not too well known at this point, but a mechanism for it’s effect would be very important to our understanding of when it will be effective and when it won’t. We DO know that zinc stops viral replication in vitro (outside of the body). One mechanism of this effect may be that it binds to an essential viral protease, thus not allowing the virus to replicate. There has also been recent evidence that Zinc ions actually block the docking of the human rhinovirus onto ICAM-1 of somatic cells. (2) This prevents the virus from binding to our respiratory tract. (3) Even though the mechanistic evidence is a bit sparse, it is definitely starting to look like Zinc binds various components that the virus needs to replicate and is effective as both a preventative and short term treatment for the common cold. (6)

When should I take Zinc?
The most effective time to take Zinc is within the first 24 hours of the onset of the symptoms. (Sooner the better). (4) It has also been shown to give beneficial effects on preventing bacterial infections and colds when taken long term. (6)

How much zinc can I take?
According to the Institute of Medicine in 2001, recommended dietary doses of Zinc is shown below.
(4)
However, in one study that demonstrated beneficial effects of zinc at reducing duration and severity of the common cold, they gave the patients a dosage of 10-23mg zinc every ~2 hours during the first 24 hours of symptom onset and only during the patient’s waking hours. (5) In this same study, they supplemented Zinc intake with 1000mg Vitamin C and found that it improved the overall effective of treatment against the cold. They mention that potential side effects of taking large amounts of Zinc was a metallic taste in your mouth or nausea. Many supplements may contain both Zinc (as Zinc citrate) and vitamin C together, but it seems to me that the proportion of vitamin C to Zinc is not optimal, as one of the leading brands combines only 10mg Zinc with 1000mg Vitamin C per dosage. It’s probably advisable to take these supplements separately. Both Zinc and Vitamin C have pretty good safety profiles, so overdosing isn’t so much of a worry. I would recommend not taking more than has been previously used in trials to stay on the safe side. But in the study (1), here is an exact quote: “Zinc lozenges slowly dissolving in the mouth over a 20–30 min period releasing adequate iZn (18 mg) used each 2 h are hypothesized to shorten common colds by 6–7 days, which is a cure for the common cold.”

(1) George A Eby, “Zinc lozenges as cure for the common cold – A review and hypothesis”, Medical Hypotheses, 74, 2010
(2)Ai Q Truong-Tran et al, “New insights into the role of zinc in the respiratory epithelium” Immunology and Cell Biology (2001) 79, 170–177
(3) Novick SG, Godfrey JC, Pollack RL, Wilder HR. Zinc-induced suppression of inflammation in the respiratory tract, caused by infection with human rhinovirus and other irritants. Med. Hypotheses 1997; 49: 347–57.
(4) Hulisz D (2004). Efficiency of zinc against common cold viruses: an overview. J. Am. Pharm. Assoc., 44: 594-603.
(5) Maggini, S, ” Combination of High-dose Vitamin C Plus Zinc for the Common Cold”, The Journal of International Medical Research, Volume 40, Number 1, January 2012 , pp. 28-42(15)
(6) Singh M et al., “Zinc for the common cold”, Cochrane Database Syst Rev. 2011 Feb 16;(2):CD001364.

Discuss!