Risks of and from SARS-CoV-2 infection and COVID-19 in people with diabetes: a systematic review of reviews

Background: This review was commissioned by the World Health Organization and presents a summary of the latest research evidence on the impact of COVID-19 in people with diabetes (PWD). Purpose: To review the evidence regarding the extent to which PWD are at increased risk of SARS-CoV-2 infection, and/or of suffering its complications including associated mortality. Data sources: We searched the Cochrane COVID-19 study register, Embase, MEDLINE, and LitCOVID on 3 December 2020. Study selection: Systematic reviews synthesising data on PWD exposed to SARS-CoV-2 infection, reporting data on confirmed SARS-CoV-2 infection, admission to hospital and/or to ICU with COVID-19, death with COVID-19. Data extraction: One reviewer appraised and extracted data; data were checked by a second. Data synthesis: Data from 112 systematic reviews were narratively synthesised and displayed using effect direction plots. Reviews provided consistent evidence that diabetes is a risk factor for severe disease and death from COVID-19. There was less data available on ICU admission, but where available this data also signalled increased risk. Within PWD, higher blood glucose levels both prior to COVID-19 illness and during COVID19 illness were associated with worse COVID-19 outcomes. Type 1 diabetes was associated with worse outcomes compared to type 2 diabetes. There was no appropriate data for discerning whether diabetes was a risk factor for acquiring SARS-CoV-2 infection. Limitations: Due to the nature of the review questions, the majority of data contributing to included reviews come from retrospective observational studies. Reviews varied in the extent to which they assessed risk of bias. Conclusions: There are no data on whether diabetes predisposes to infection with SARS-CoV-2. Data consistently show that diabetes increases risk of severe COVID-19. As both diabetes and worse COVID-19 outcomes are associated with socioeconomic disadvantage, their intersection warrants particular attention.