OBJECTIVE This study investigated the effects of severe hypoglycemia on risks of all-cause mortality and cardiovascular disease (CVD) incidence in patients with type 1 diabetes mellitus (T1DM).

RESEARCH DESIGN AND METHODS Two nested case-control studies with age- and sex-matched control subjects and using the time-density sampling method were performed separately within a cohort of 10,411 patients with T1DM in Taiwan. The study enrolled 564 nonsurvivors and 1,615 control subjects as well as 743 CVD case subjects and 1,439 control subjects between 1997 and 2011. History of severe hypoglycemia was identified during 1 year, 1–3 years, and 3–5 years before the occurrence of the study outcomes. Conditional logistic regression analyses were performed to estimate the odds ratio (OR) and 95% CI of the study outcomes.

RESULTS Prior severe hypoglycemic events within 1 year were associated with higher risks of all-cause mortality and CVD (adjusted OR 2.74 [95% CI 1.96–3.85] and 2.02 [1.35–3.01], respectively). Events occurring within 1–3 years and 3–5 years before death were also associated with adjusted ORs of 1.94 (95% CI 1.39–2.71) and 1.68 (1.15–2.44), respectively. Significant dose–gradient effects of severe hypoglycemia frequency on mortality and CVD were observed within 5 years.

CONCLUSIONS Although the CVD incidence may be associated with severe hypoglycemic events occurring in the previous year, the risk of all-cause mortality was associated with severe hypoglycemic events occurring in the preceding 5 years. Exposure to repeated severe hypoglycemic events can lead to higher risks of mortality and CVD.