AimWe explored the effectiveness of continuous glucose monitoring for 1 year on glycated A1c reduction in adults with type 1 diabetes mellitus.MethodsWe included type 1 diabetes mellitus adults who were either new continuous glucose monitoring users (N= 155) or non-users who were under standard care (N= 384). Glycated A1c was measured at baseline and 3, 6, 9, and 12 months. Individuals with (N= 155) or without continuous glucose monitoring use (N= 310) were matched 1:2 by propensity score. We used the linear mixed models to identify the quantitative reduction in repeated measures of glycated A1c.ResultsThe change in glycated A1c from baseline to 12 months was −0.5% ± 1.0% for the continuous glucose monitoring user group (N= 155,P< 0.001) and −0.01% ± 1.0% for the non-user group (N= 310,P= 0.816), with a significant difference between the two groups (P= 0.003). Changes in glycated A1c were significant at 3, 6, 9, and 12 months compared with those at baseline in patients using continuous glucose monitoring (P< 0.001), and the changes differed significantly between the groups (P< 0.001). A linear mixed model showed an adjusted treatment group difference in mean reduction in glycated A1c of −0.11% (95% confidence interval, −0.16 to −0.06) each three months. In the continuous glucose monitoring user group, those who achieved more than 70% of time in range significantly increased from 3 months (37.4%) to 12 months (48.2%) (P< 0.001).ConclusionIn this longitudinal study of type 1 diabetes mellitus adults, the use of continuous glucose monitoring for 1 year showed a significant reduction in glycated A1c in real-world practice.