This is a Danish study based on registry results. 
Among 4,725 children and adolescents with type 1 diabetes identified, 1,035 were diagnosed with at least one psychiatric disorder. High average HbA1c levels during the first 2 years after diagnosis predicted higher risk of psychiatric diagnoses. Patients with psychiatric comorbidity had higher HbA1c levels (0.22% [95% CI 0.15; 0.29]; 2.40 mmol/mol [1.62; 3.18]; P < 0.001) and an increased risk of hospitalization with diabetic ketoacidosis (1.80 [1.18; 2.76]; P = 0.006).
1 Sildorf SM, Breinegaard N, Lindkvist EB, et al. Poor metabolic control in children and adolescents with type 1 diabetes and psychiatric comorbidity. Diabetes Care 2018;41:2289–96. doi:10.2337/dc18-0609