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Prevalence of Thyroid Dysfunction in Autoimmune and Type 2 Diabetes: The Population-Based HUNT Study in Norway
Hanne F Fleiner1, Trine Bjøro1, Kristian Midthjell1
1Department of Cancer Research and Molecular Medicine (H.F.F., V.G.), Norwegian University of Science and Technology, N-7491 Trondheim, Norway; Departments of Clinical Pharmacology (H.F.F.) and Endocrinology (V.G., B.O.Å.), St Olavs Hospital, N-7006 Trondheim, Norway; Department of Medical Biochemistry (T.B.), Oslo University Hospital, N-0424 Oslo, Norway; Institute of Clinical Medicine (T.B.), Faculty of Medicine, University of Oslo, N-0316 Oslo, Norway; and HUNT Research Center, Department of Public Health and General Practice (K.M., B.O.Å.), Norwegian University of Science and Technology, N-7600 Levanger, Norway.
Context:
Associations between autoimmune diabetes and autoimmune thyroid disease are known but insufficiently characterized. Some evidence suggests that type 2 diabetes may also be associated with hypothyroidism.
Objective:
The objective of the study was to investigate associations of autoimmune and type 2 diabetes with the prevalence of hypo- and hyperthyroidism.
Design And Setting:
This was a cross-sectional, population-based study of adults in two surveys of the Nord-Trøndelag Health (HUNT) Study.
Participants:
A total of 34 235 participants of HUNT2 (1995-1997) and 48 809 participants of HUNT3 (2006-2008) participated in the study.
Main Outcome Measures:
Prevalence of hypo- and hyperthyroidism was estimated, assessed by self-report, serum measurements, and linkage with the Norwegian Prescription Database.
Results:
In HUNT2, autoimmune diabetes was associated with a higher age-adjusted prevalence of hypothyroidism among both women (prevalence ratio 1.79, 95% confidence interval [CI] 1.30-2.47) and men (prevalence ratio 2.71, 95% CI 1.76-4.19), compared with having no diabetes. For hyperthyroidism, the corresponding cumulative prevalence ratios were 2.12 (95% CI 1.36-3.32) in women and 2.54 (95% CI 1.24-5.18) in men with autoimmune diabetes. The age-adjusted excess prevalence of hypothyroidism (∼6 percentage points) and the presence of thyroid peroxidase antibodies (8-10 percentage points) associated with autoimmune diabetes was similar in women and men. Type 2 diabetes was not associated with the prevalence of hypothyroidism. In HUNT3, associations were broadly similar to those in HUNT2.
Conclusions:
Autoimmune diabetes, but not type 2 diabetes, was strongly and gender neutrally associated with an increased prevalence of hypo- and hyperthyroidism and the presence of thyroid peroxidase antibodies. Increased surveillance for hypothyroidism appears not necessary in patients with type 2 diabetes.