Diabetes mellitus is challenging in the context of the COVID-19 pandemic. The prevalence of diabetes patients hospitalized in intensive care units for COVID-19 is two- to threefold higher, and the mortality rate at least double, than that of non-diabetes patients. As the population with diabetes is highly heterogeneous, it is of major interest to determine the risk factors of progression to a more serious life-threatening COVID-19 infection. This brief review discusses the main findings of CORONADO, a prospective observational study in France that specifically addressed this issue as well as related observations from other countries, mainly China and the US. Some prognostic factors beyond old age have been identified: for example, an increased body mass index is a major risk factor for requiring respiratory assistance. Indeed, obesity combines several risk factors, including impaired respiratory mechanics, the presence of other comorbidities and inappropriate inflammatory responses, partly due to ectopic fat deposits. While previous diabetic microvascular (renal) and macrovascular complications also increase risk of death, the quality of past glucose control had no independent influence on hospitalized diabetes patient outcomes, but whether the quality of glucose control might modulate risk of COVID-19 in non-hospitalized diabetes patients is still unknown. In addition, no negative signs regarding the use of RAAS blockers and DPP-4 inhibitors and outcomes of COVID-19 could be identified. Hyperglycaemia at the time of hospital admission is associated with poor outcomes, but it may simply be considered a marker of severity of the infection. Thus, the impact of glucose control during hospitalization on outcomes related to COVID-19, which was not investigated in the CORONADO study, is certainly deserving of specific investigation.
