Diabetes and Susceptibility to COVID-19: Risk Factors and Preventive and Therapeutic Strategies

Coronavirus disease 2019 (COVID-19) is a highly infectious disease caused by a novel human coronavirus called severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Diabetes is a well-known risk factor for infectious diseases with high prevalence and increased severity. Here, we elucidated the possible factors for the increased vulnerability of diabetic patients to SARS-CoV-2 infection and the more severe COVID-19 illness. The worsened prognosis of patients with both COVID-19 and diabetes may be attributable to host receptor angiotensin-converting enzyme 2-assisted viral uptake. Moreover, insulin resistance is often associated with impaired mucosal and skin barrier integrity, resulting in mic-robiota dysbiosis, which increases susceptibility to viral infections. It may also be associated with higher levels of pro-inflammatory cytokines resulting from an impaired immune system in diabetics, inducing a cytokine storm and excessive inflammation. This review describes diabetes mellitus and its complications, explains the risk factors, such as disease characteristics and patient lifestyle, which may contribute to the high susceptibility of diabetic patients to COVID-19, and discusses preventive and therapeutic strategies for COVID-19-positive diabetic patients.