Sunday, October 4, 2020

Zinc and treating the common cold



Since 1974, when a study titled “Zinc ions inhibit replication of rhinoviruses” by Korant, Kauer, and Butterworth was published in the journal Nature, the idea that zinc can prevent or cure the common cold has circulated. Many studies have looked at different zinc ionophores and lozenge formulas and their effect on the course of cold symptoms, as well as the potential biochemical mechanism at work. Though the exact mechanism of action is still unknown, there is some consensus that ionized zinc affects picornaviruses.


Zinc Against Cold Viruses


Rhinoviruses, of the family Picornaviridae, are only one type of almost 200 viruses that cause the acute respiratory infection symptoms known as the common cold. However, rhinoviruses are estimated to cause one-third to half of all colds, and preventing rhinovirus infections would severely limit the most common human infection.

Since the 1970s, studies have found that zinc ions may inhibit rhinovirus replication. Viral replication plays an important role in infection; inhibiting replication would prevent progression of the disease and ease symptoms. In addition, zinc ions have an affinity for the ICAM-1 receptor, which is bound by rhinovirus when infecting cells in the respiratory tract. Zinc binding the ICAM-1, or the rhinovirus-ICAM complex, would prevent infection of the nasal epithelium, preventing the duration of the common cold.

What Type of Zinc Reduces Cold Symptoms?

In the 1980s and 1990s, zinc gluconate lozenges were shown in some studies to decrease the duration of cold symptoms if taken within 24 hours of symptom onset, whereas other studies had no success. Zinc acetate lozenges appeared to have a better success rate, likely because of their formulation. The problem seems to lie in the concentration of ionic zinc in commercially available lozenges. The ionic zinc concentration is not measurable by the label on a package, it is dependent on what is released as the lozenge dissolves in the mouth over a period of time.

Zinc gluconate gels and nasal sprays have had experimental success in alleviating rhinovirus infection. Some formulations were even marketed, such as Zicam. However, these products were recently warned against due to users losing their sense of smell.

Potential Problems with Zinc Products

Though zinc lozenges have repeatedly been found to exert no side effects or create any problems, beyond the chalky taste, zinc nasal sprays have been shown to irreversibly damage the nasal lining. In particular, Zicam (zinc gluconate nasal spray from Matrixx Initiatives) was shown in an October 2009 study to have cytotoxic effects on both mouse and human olfactory sensory neurons, as well as a near complete loss of the nasal epithelium and submucosa. Sprays not containing zinc did not have this significant effect, indicating that the zinc was cytotoxic to the nasal mucosa.

Using Zinc to Stop a Cold

Though it is far from being a cure, there is evidence to suggest that zinc lozenges may help reduce cold symptoms, cutting the duration of the illness in half and alleviating symptoms more fully after the duration of the illness. A 2011 Cochrane Review concluded that zinc supplementation can reduce the duration and severity of a cold, though the change in duration is mostly by just 1 day. However, the exact mechanism of action is not known, and the exact dosage will differ by product. The guidance is to start with lozenges or tablets within 24 hours of the onset of a cold. In a 2017 meta-analysis, zinc acetate and zinc gluconate were shown to have similar effectiveness.

More studies are needed to better quantify zinc’s effect on rhinovirus and other cold viruses in order to reap the full benefit of this element.

Additional References:

Eby. Zinc lozenges as cure for the common cold: A review and hypothesis. Medical Hypotheses. 2009; doi 10.1016/j.mehy.2009.10.017

Hulisz. Efficacy of zinc against common cold viruses: An overview. Journal of the American Pharmacists Association. 2004; 44(5). Available on the Medscape website.

Lim et al. Zicam-induced damage to mouse and human nasal tissue. Public Library of Science (PLoS) One. 2009; 4(10), e7647.


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