The Impact of Insulin Dosage on Cancer Risk in Type 1 Diabetes: A Population-Based Study

OBJECTIVES: Type 1 diabetes (T1D) is a lifelong disease requiring long-term insulin therapy to prevent complications. Many studies have reported that patients with type 2 diabetes have higher risk of developing certain cancers; however, the association remains unclear among type 1 diabetes. This study aimed to investigate the association between insulin dose and cancer incidence among individuals with T1D using a population-based database.

METHODS: This retrospective cohort study analyzed data from the National Health Insurance Research Database, Catastrophic Illness Registry, and Taiwan Cancer Registry data (2010-2021) for 10,248 type 1 diabetes patients and categorizing daily insulin doses into four groups by percentiles. The primary outcome was cancer incidence, while the secondary outcome was all-cause mortality. Time-to-event analysis was performed using Kaplan-Meier and Cox proportional hazard models, considering insulin dose as time-varying variable.

RESULTS: During the 12-year follow-up period, the incidence rate (IR) for cancer in the low-dose group was 5.27 per 1000 person-years (IQR: 4.27–6.45), decreasing to 1.54 per 1000 person-years in the high-dose group. The IR for all-cause mortality was 10.82 per 1000 person-years in the low-dose group and 2.16 per 1000 person-years in the high-dose group. When considering the time-varying dose of insulin, the high-dose group demonstrated the lowest risk for cancer incidence (HR=0.55, 95% CI: 0.37-0.81), consistent with the fixed-dose model (HR=0.42, 95% CI: 0.28-0.64). The IR for invasive and metastatic cancer also decreased in the medium-high and high-dose groups, and all-cause mortality was inversely related (HR=0.49, 95% CI: 0.34-0.71; HR=0.42, 95% CI: 0.30-0.58). Additionally, cancer related to the digestive organs and peritoneum was the most common incident cancer (45.52%).

CONCLUSIONS: T1D patients with higher daily insulin doses show a reduced risk of developing cancer, a lower incidence of invasive or metastatic cancer, and decreased all-cause mortality. These findings provide insights into insulin doses in T1D patients and inform clinical decision-making.