Zinc and Coronavirus Disease 2019: Causal or Casual Association?

To the Editor:

We read with interest the article by Yao et al this issue of CHEST whereby they have studied the effect of zinc supplementation in hospitalized patients of coronavirus disease 2019 (COVID-19) infection. In reference to the patient assessment parameters and results, one very important aspect needs attention. Although the authors have evaluated in detail the baseline clinical and treatment characteristics, they have no data pertaining to serum zinc levels before or after zinc supplementation. We do understand because this was a retrospective analysis with waiver of consent, but one should be cautious about the interpretation of results in this scenario. Before concluding that zinc supplementation did not lead to a statistically significant decrease in mortality or other outcome parameters, we should have data clarifying which patients were zinc deficient and which were not before receiving zinc supplementation. This could have been done by measuring serum zinc levels. It is well mentioned in literature that patients with certain respiratory illnesses, for example, asthma, have decreased serum zinc levels. Ibraheem et al recorded the prevalence of 98.3% for low serum zinc levels in children with acute lower respiratory tract infection than that in control subjects of 64.2%. Rerksuppaphol and Rerksuppaphol have also shown that zinc supplementation reduces the number of hospital days in children with acute lower respiratory tract infection, and their results were substantiated by measuring pre and post supplementation serum zinc levels. Serum zinc level is also the recommended modality to estimate dietary zinc status in individuals. Also, in COVID-19 disease, C-reactive protein has emerged as one of the key inflammatory markers, and serum zinc levels also have been found to be inversely proportional to C-reactive protein levels in some surveys. This further highlights the importance of getting serum zinc levels before making any conclusions about zinc therapy in such patients. The work done by the authors is worth appreciation; however, a prospective cohort study with pre and post zinc supplementation zinc levels would probably yield better or probably different answers.