BackgroundPrevious studies comparing insulin degludec/insulin aspart (IDegAsp) with premixed insulin twice daily among insulin users with type 2 diabetes have not thoroughly investigated differences in the glucose variability and psychological evaluations related to insulin regimen changes. We investigated changes in the daily and day-to-day glucose variability and quality of life (QOL) related to insulin use in patients with type 2 diabetes during a switch from premixed insulin preparations comprising either human insulin (BHI30) or insulin aspart (BIAsp30) to IDegAsp twice daily.MethodsIn this prospective observational study, 22 subjects (BHI30:BIAsp30 = 12:10) self-measured their blood glucose levels every morning, and before and after all meals each week. Premixed insulin was administered for the first 2 months, followed by IDegAsp for the next 2 months. Efficacy measures were evaluated during the last month or last day of both phases.ResultsThe mean blood glucose levels (175.5 vs. 163.0 mg/dL; P = 0.004) and the M-values (53.9 vs. 27.6; P = 0.049) were significantly lower in the IDegAsp phase. However, no differences in the standard deviations of morning fasting glucose levels were observed between phases (premixed vs. IDegAsp, 20.0 vs. 19.3 mg/dL; P = 0.343). Compared to the premixed phase, the before-breakfast (145.3 vs. 126.0 mg/dL; P < 0.001), after-breakfast (190.3 vs. 170.7 mg/dL; P = 0.001), before-dinner (153.0 vs. 140.1 mg/dL; P  = 0.007), and after-dinner glucose levels (198.7 vs. 181.4 mg/dL; P = 0.018) were lower in the IDegAsp phase. However, the before-lunch (150.8 vs. 148.2 mg/dL; P  = 0.329) and after-lunch glucose levels (214.7 vs. 211.4 mg/dL; P = 0.308) did not significantly differ between phases. Regarding QOL, the total and therapy-related feeling Insulin Therapy Related-QOL (ITR-QOL) questionnaire scores favored IDegAsp, as did the ITR-QOL at Night questionnaire subscale score of glycemic control before breakfast.ConclusionsAlthough the day-to-day variability of morning fasting glucose levels did not change, switching to IDegAsp improved daily glucose level variability, the morning and evening glucose control and QOL among patients treated with premixed insulin.Trial registration University Hospital Medical Information Network Clinical Trials Registry, UMIN000021939. Prospectively registered 18 April 2016