Researchers have identified robust, gender-neutral associations between autoimmune diabetes and an increased prevalence of hypothyroidism and hyperthyroidism and the presence of thyroid peroxidase antibodies.
However, no such associations appear to exist between type 2 diabetes and thyroid dysfunction.
Researchers evaluated data on residents of Nord-Trondelag County in Norway who participated in two surveys of the HUNT study. HUNT2 (1995-1997; n – 34,235) and HUNT3 (2006-2008; n = 48,809) included thorough questionnaires, clinical examinations and nonfasting blood samples. Prevalence of hypo- and hyperthyroidism were determined through patient self-report, blood values and information obtained through linkage with the Norwegian Prescription Database regarding prescriptions for levothyroxine and thioamides. Autoimmune diabetes was determined by testing fasting serum samples for antibodies against glutamic acid decarboxylase (GADA). Participants were classified as having diabetes based on a negative GADA test.
Researchers evaluated the rates of thyroid dysfunction by diabetes type and determined ratios of prevalence in patients with autoimmune or type 2 diabetes to participants without diabetes.
In the HUNT2 population, the researchers found an association between autoimmune diabetes and higher age-adjusted prevalence of hypothyroidism in women (prevalence ratio [PR] = 1.79; 95% CI, 1.3-2.47) and men (PR = 2.71; 95% CI, 1.76-4.19) compared with patients without diabetes; similar associations were found in HUNT3. After adjustment for age, the surplus prevalence of hypothyroidism (6 percentage points) and the detection of thyroid peroxidase antibodies (8-10 percentage points) in association with autoimmune diabetes was comparable in women and men.
In HUNT2, an association was found between autoimmune diabetes and higher age-adjusted cumulative rate of hyperthyroidism in both women (PR = 2.12; 95% CI, 1.36-3.32) and men (PR = 2.54; 95% CI, 1.24-5.18) compared with no diabetes. In HUNT3, these associations were similar in men only; no association was found between hyperthyroidism and autoimmune diabetes in women.
In HUNT2, no association was found between the overall prevalence of hypothyroidism and type 2 diabetes. Type 2 diabetes was linked to a slightly higher rate of hypothyroidism in women (PR = 1.24; 95% CI, 1.04-1.47) and men (PR = 1.25; 95% CI, 0.93-1.67) in HUNT3.
“The findings support the recommendation of regular follow-up of thyroid function in people with autoimmune diabetes,” the researchers wrote. “On the other hand, our results do not support proposals for increased surveillance of hypothyroidism in people with type 2 diabetes.” – by Jennifer Byrne
The researchers report no relevant financial disclosures.