Hyperthyroidism Induces Glucose Intolerance by Lowering Both Insulin Secretion and Peripheral Insulin Sensitivity
Weranuj Roubsanthisuk MD*, Praneet Watanakejorn PN*, Monchaya Tunlakit BPH*, Sutin Sriussadaporn MD*
Affiliation : * Department of Medicine, Faculty of Medicine Siriraj Hospital, Mahidol University
Objective : The objectives of this study were to examine the effects of hyperthyroidism on glucose tolerance,
insulin secretion, and insulin sensitivity.
Materials and Methods : Thirty-eight patients with hyperthyroidism and twenty-six healthy volunteers with
matching age and body mass index were included. Patients with conditions known to affect glucose metabo-
lism were excluded. An oral glucose tolerance test was performed after the diagnosis of hyperthyroidism and
again when they achieved euthyroid state. Areas under the glucose and insulin curves were used to assess
plasma glucose and insulin responses, respectively. β-cell function was determined by the corrected insulin
response (CIR) and homostatic model assessment model 2 (HOMA2-%B). Peripheral insulin sensitivity was
determined by the insulin activity (IA) and HOMA2-%S.
Result: The prevalence of glucose intolerance in hyperthyroid state was 39.4% [impaired glucose tolerance
(IGT) 31.5% and diabetes mellitus (DM) 7.9%]. This was significantly higher than that of 30.7% [IGT 19.2%
and DM 11.5%] in healthy volunteers (p < 0.05). Glucose intolerance was associated with higher systolic
blood pressure, higher mean arterial pressure, lower CIR, and higher T4 levels but not with the levels of T3. IA
and HOMA2-%S significantly improved when achieving a euthyroid state despite the increase in body mass
index.
Conclusion : In conclusion, glucose intolerance is common in hyperthyroidism. Both impaired insulin secre-
tion and decreased peripheral insulin sensitivity are the factors contributing to the development of abnormal
glucose tolerance in the hyperthyroid state.
Keywords : Hyperthyroidism, Oral glucose tolerance, Diabetes mellitus, Insulin resistance
