Factors associated with impaired awareness of hypoglycemia in adult patients with type 1 and type 2 diabetes mellitus: a systematic review and meta-analysis

Background Impaired awareness of hypoglycemia (IAH) is a high-risk complication of diabetes that attenuates patients’ ability to perceive early warning symptoms of hypoglycemia, significantly increasing the risks of severe hypoglycemia, hypoglycemic coma, and all-cause mortality. However, no systematic synthesis of factors associated with IAH specifically in adults with type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM) is currently available. This study aimed to systematically review factors associated with IAH in adults with T1DM and T2DM, providing evidence-based support for clinical screening of high-risk populations and the development of preventive strategies. Methods A systematic computerized search was conducted across eight Chinese and English databases, including PubMed, Embase, Web of Science, Cochrane Library, the Ovid platform, China National Knowledge Infrastructure, Wanfang Data, and VIP Database, with the search period from inception to January 2026. Cross-sectional studies, cohort studies, and case-control studies investigating factors associated with IAH in adults with T1DM or T2DM were included. Effect estimates, IAH definitions, original effect measures, adjustment status, and reported covariates were extracted. The Joanna Briggs Institute Critical Appraisal Checklist was used to assess the quality of cross-sectional studies, and the Newcastle-Ottawa Scale was used for cohort and case-control studies. RevMan 5.4 software was used for meta-analysis of factors reported by at least two sufficiently comparable studies; sparse pooled estimates were interpreted cautiously. Results A total of 12 studies involving 16,086 adults with T1DM or T2DM from eight countries were included. Seven factors were quantitatively synthesized. History of severe hypoglycemia (OR = 3.83, 95% CI 1.76–8.33), diabetes duration (OR = 1.03 per year, 95% CI 1.02–1.04), and microvascular/diabetes-related complications (OR = 1.96, 95% CI 1.35–2.84) were associated with IAH. Across sensitivity analyses, severe-hypoglycemia history and diabetes duration were the most robust findings; age, female sex, and HbA1c were study- or design-sensitive, BMI was inconclusive, and the complications estimate remained exploratory. Conclusion History of severe hypoglycemia and longer diabetes duration were the most consistent factors associated with IAH in adults with T1DM and T2DM. These findings may support risk-focused screening, closer assessment of hypoglycemia awareness, and the development of preventive strategies. Causality cannot be inferred; prospective studies using standardized IAH definitions and prespecified adjustment models are needed to confirm these associations and clarify their temporal relationships. Clinical trial number Not applicable.