Zinc is an important trace mineral that plays a crucial role in growth, development, and maintenance of immune function. Zinc deficiency is common and may be result of lifestyle, age, certain disease-mediated factors (liver cirrhosis, inflammatory bowel disease) , and malnourishment.
A mounting evidence accumulated over 50 years of research demonstrates that zinc has antiviral effect against variety of viruses via numerous mechanisms. Zinc can have a direct antiviral effect, but it also can generate innate and acquired antiviral immune system responses.
It has been demonstrated in many studies that zinc inhibits replication of RNA viruses such as influenza, poliovirus and coronavirus. The studies have also shown that zinc has inhibitory effect on many other viruses such as HPV, HIV, Varicella Zoster, HSV and Hepatitis C.
Another important factor is the intracellular concentration of zinc. To be efficient in fighting viruses, zinc has to be able to enter the cells and maintain a sufficient concentration. Substances that help zinc transport inside the cells are called zinc-ionophores. Substances such as pyrithione and quercetin are zinc-ionophores.
A study published in 2010, demonstrated that combined action of pyrithione and zinc was very efficient in inhibiting influenza, poliovirus and coronavirus.
Although no studies have been done on efficacy of combined action of quercetin and zinc in inhibiting these viruses, it could be assumed that they can have similar effect, since quercetin is capable of transporting zinc into the cells, thus increasing the intracellular concentration of zinc.
Both quercetin and zinc are safe supplements and adding them during flu and cold season may be very beneficial. Covid-19 is caused by a coronavirus and previous studies have shown that zinc was efficient in inhibiting SARS virus (Covid-19 is caused by SARS covariant coronavirus.).
Quercetin and zinc are also readily available in food. Quercetin rich foods are: onion, watercress, radicchio, asparagus, kale, red leaf lettuce, elderberry, cranberry, blueberry, apple and other. Zinc rich food are: red meat, shellfish, legumes, nuts, dairy, eggs and other. So, bolster your antiviral defenses and Bon Appetit!
*It is interesting to note that hydroxychloroquine is also a zinc-ionophore which may explain why many doctors used it in combination with zinc for covid-19 patients.
[1 ]Read, S. A., Obeid, S., Ahlenstiel, C., & Ahlenstiel, G. (2019). The Role of Zinc in Antiviral Immunity. Advances in Nutrition, 10(4), 696-710. doi:10.1093/advances/nmz013
 Velthuis, A. J., Sjoerd H. E. Van Den Worm, Sims, A. C., Baric, R. S., Snijder, E. J., & Hemert, M. J. (2010). Zn2 Inhibits Coronavirus and Arterivirus RNA Polymerase Activity In Vitro and Zinc Ionophores Block the Replication of These Viruses in Cell Culture. PLoS Pathogens, 6(11). doi:10.1371/journal.ppat.1001176