The story of COVID-19 and the science behind the pandemic is evolving rapidly every day, with a flurry of publications in various clinical and preclinical journals.
Here, I summarize the known and unknown links between diabetes and COVID-19, focusing on three pertinent clinical questions.
How does diabetes affect the risk for COVID-19 infection?
Just as with other respiratory illnesses, such as influenza A, it appears that diabetes increases the risk for COVID-19 infection, although no prevalence studies comparing people with and without diabetes for COVID-19 have been published to support this presumption.
Several studies from China, Italy, and the United States suggest that diabetes increases risks for severe COVID-19 complications and mortality. In one Chinese study, people with diabetes had the second highest fatality rate (7.3%) after cardiovascular disease (CVD; 10.5%) among those with comorbid conditions.
Although several questions regarding mechanisms responsible for increased severity of COVID-19 with diabetes need to be investigated (immune dysfunction, link to comorbidities such as hypertension or obesity, link to complications such as CVD or nephropathy), the single most important outstanding clinical question in my mind is: What is the role of achieving euglycemia in COVID-19 infection and its severity? That is, does improving glucose control (chronically in an outpatient setting or acutely in an inpatient setting) result in primary prevention of COVID-19 infection or reduce its complications and fatality?
a recent data analysis for hospitalized patients with COVID-19 suggested a much higher mortality rate and increased length of stay among those who developed hyperglycemia during their hospital stay but had no evidence of diabetes before being admitted. Similarly, a previous publication had found an independent association between fasting glucose at hospital admission and severity of H1N1.
The question that needs to be explored further in both type 1 and type 2 diabetes, however, is whether acute hyperglycemia is truly an independent causal factor or simply a marker for increased severity and mortality from COVID-19.
Additional investigations into the efficacy (or at least safety) of common diabetes medications in relation to COVID-19 infection would be of clinical interest. Specifically, ACE2 and DPP-4 have been identified as receptors for the coronavirus and a related virus. Some reassurance on the safety of ACE inhibitors and angiotensin receptor blockers with COVID-19 hospitalizations is provided by recent retrospective study publications.