Supplementary Material for: Glycaemic control and BMI in children with type 1 diabetes with and without celiac disease - A longitudinal national cohort study

Background: The risk of celiac disease (CD) is high in children with type 1 diabetes (T1D). While some studies have linked CD in children with T1D to impaired growth and poorer glycaemic control, results have been inconsistent. Further, no study has examined the relevance of whether the diagnosis of CD is established before, in conjunction with, or after T1D. Objectives: To examine whether CD influences body mass index (BMI) and glycaemic control in children with T1D, and whether the timing of the onset of CD is of relevance. Methods: Swedish children diagnosed with T1D between 2005 and 2010 who were enrolled in the Better Diabetes Diagnosis study (N = 3612; >90% national coverage) were included. The participants were screened for CD at T1D diagnosis and annually for five years. BMI (BMI-SDS), glycaemic control (HbA1c) and diabetes ketoacidosis (DKA) were assessed at T1D diagnosis, BMI-SDS and HbA1c at five annual follow-ups. Results: Children diagnosed with CD at the same time as the T1D diagnosis had statistically significantly lower BMI-SDS compared to children without a CD diagnosis at all follow-up assessments. Children diagnosed with CD before T1D had a significantly lower BMI-SDS during the first two years of follow-up. CD status was not associated with HbA1c or DKA at T1D diagnosis or during follow-up. Conclusion: Children diagnosed with T1D with known or identified CD at the time of diagnosis had a lower BMI-SDS up to five years after T1D diagnosis and may require additional nutritional support. The presence or timing of a CD diagnosis do not appear to be associated with glycaemic control in children with T1D.