Association between diabetes mellitus and COVID-19 severity in hospitalized adults: A systematic review and meta-analysis

As novel SARS-CoV-2 variants continue to emerge, severe COVID-19 remains a major public health challenge. Diabetes mellitus is a globally prevalent metabolic disorder that has been identified as a potential risk factor for severe COVID-19. However, the consistency and magnitude of this association remain unclear across populations. We conducted a systematic review and meta-analysis of 29 observational studies from PubMed, Scopus, and Google Scholar published between 2020 and 2024, including 13,682 COVID-19 patients across 15 countries. Data were pooled using a random-effects model. Subgroup analyses and meta-regression were performed to assess the impact of geographic region, sample size, and study quality. Publication bias was evaluated using funnel plots and Egger’s test. Diabetes prevalence was higher among patients with severe COVID-19 compared with those with non-severe disease (Odds Ratio [OR] = 3.27, 95% CI 2.11–5.08, p < 0.00001). No evidence of significant publication bias was detected. It should be noted that most included studies were observational and unadjusted for key confounders. These findings suggest an association between diabetes and severe COVID-19. Given that the evidence is largely derived from unadjusted observational data, causal inference cannot be established. Nevertheless, awareness of diabetes as a potential risk factor may inform monitoring and preventive strategies, with consideration of coexisting comorbidities and regional healthcare disparities.