Celiac Disease Increases Risk of Thyroid Disease in Patients With Type 1 Diabetes: A Nationwide Cohort Study.

OBJECTIVE Both type 1 diabetes (T1D) and celiac disease (CD) have been linked to autoimmune thyroid disease (ATD). We examined if individuals with both T1D and CD were at a higher risk of ATD than those with only T1D. RESEARCH DESIGN AND METHODS This study was a nationwide population-based cohort study. We defined T1D as having an inpatient or a hospital-based outpatient diagnosis of T1D at age ≤30 years in the Swedish National Patient Register between 1964 and 2009. Data on CD were obtained through small intestinal biopsy reports showing villous atrophy (Marsh histopathology grade III) between 1969 and 2008 at any of the 28 pathology departments in Sweden. ATD included hyperthyreosis and hypothyreosis, defined according to the Swedish National Patient Register. We identified 947 individuals with T1D and biopsy-verified CD. These were matched to 4,584 control subjects with T1D but no CD diagnosis. Cox regression then estimated the risk of ATD. RESULTS Among T1D, CD was a risk factor for later ATD. During follow-up, 90 T1D+CD patients developed ATD (expected n = 54). Adjusting for sex, age, and calendar period, this corresponded to a hazard ratio (HR) of 1.67 (95% CI 1.32-2.11; P < 0.001). This excess risk was highest in those who had CD for 10 years or more (HR 2.22 [95% CI 1.49-3.23]). Risk increases were seen in both males and females. CD was a risk factor for both hypothyreosis (HR 1.66 [95% CI 1.30-2.12]) and hyperthyreosis (HR 1.72 [95% CI 0.95-3.11]). CONCLUSIONS Among patients with T1D, CD is a risk factor for the later development of ATD.