Thyroid function changes and COVID-19 severity: egg or chicken?

The novel coronavirus disease 2019 (COVID-19) produced by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a highly contagious infectious disease. In addition to typical flu-like symptoms, COVID-19 can also cause extrapulmonary spread and systemic inflammation, potentially causing multiorgan dysfunction, including thyroid dysfunction. Thyroid function changes in patients with COVID-19 have been widely reported, but the results are inconsistent. Based on available data, SARS-CoV-2 infection can lead to changes in thyroid function, and the degree of thyroid function changes was positively correlated with the severity of COVID-19, which involved multiple potential mechanisms. In contrast, current evidence was insufficient to prove that thyroid function changes could induce the progression of COVID-19 clinical deterioration.