Impacts Of Glycosylated Hemoglobin And Body Mass Index On Thyroid Hormones

Objectives:1. The purpose of this study was to investigate the impacts of Glycosylated hemoglobin (HbAlc) on thyroid hormones in type 2 diabetes.2. To evaluate the association between BMI and thyroid hormones in euthyroidism.Methods:1. A retrospective study was carried out among 994 diabetic patients from endocrinology department and 2279 non-diabates from physical center in our hospital, and their thyroid functions were evaluated.2.835 type 2 diabetic subjects without thyroid disease and 835 sex and age (± 2yrs) matched non-diabetic subjects were assigned to diabetic group and non-diabetic group. Fasting blood draw were taken to detect liver enzymes, lipids, fasting blood-glucose (FPG), glycosylated hemoglobin (HbAlc), thyroid function; then thyroid hormones were compared between the two groups, and multiple linear regression models were used to analyze the relationship between thyroid hormones and HbAlc.3. Total of 2097 examinees in our hospital were included in this study. The subjects were assign to non-obese group (BMI< 24kg/m2) and overweight and obese group (BMI> 24kg/m2) according to BMI. Fasting blood draw were taken to detect liver enzymes, lipids, FPG, HbAlc and thyroid hormones. Logistical regression models were presented to evaluate corrections between BMI and thyroid hormones. Results:1. The overall prevalence rate of thyroid disease was 13.6% in 994 type 2 diabetic patients, and the commonest diagnosis was sub-clinical hypothyroidism (11.07%), followed by hypothyroidism (1.41%), sub-clinical hyperthyroidism (0.6%), and hyperthyroidism (0.5%); In contract, the overall prevalence rate of thyroid disease was 7.99% in 2347 non-diabetic patients, and the commonest diagnosis was sub-clinical hypothyroidism (5.97%), followed by hypothyroidism (1%), sub-clinical hyperthyroidism (0.61%), and hyperthyroidism (0.39%).2. Female patients with type 2 diabetes had higher risk of developing thyroid disease than male patients (19.7% vs.9.1%, P< 0.05). Moreover, the prevalence of hypothyroidism (including clinical and sub-clinical hypothyroidism) significantly increased with age and diabetes duration (P for trend< 0.05), however, the prevalence of hyperthyroidism (including clinical and sub-clinical hypothyroidism) did not show up or down trend with increasing of age or diabetes duration (P for trend> 0.05).3. Free triiodothyronie (FT3), FT3/FT4 and thyrotropin (TSH) in diabetic group were significantly lower than those in non-diabetic group (P< 0.05).4. Diabetes treated with metformin, insulin or metformin combined with insulin had lower levels of serum FT3 and FT3/FT4 than those treated with non-metformin oral hypoglycemic agents (4.29 ± 0.85,4.13 ± 0.74 and 4.26 ± 0.83 vs.4.46 ± 0.76 for FT3; 0.26 ± 0.06,0.26 ± 0.05 and 0.27 ± 0.06 vs.0.28 ± 0.05 for FT3/FT4, P< 0.05).5. In type 2 diabetic subjects, serum FT3, FT3/FT4 and TSH were decreased (P for trend< 0.001), but serum FT4 were increased with the increasing tertiles of HbAlc (P for trend< 0.001). In type 2 diabetic subjects, the prevalence of NTIS increased with the increasing tertiles of HbAlc, the prevalence of low T3 syndrome and low T4 syndrome also increased with the increasing tertiles of HbAlc (P for trend< 0.05).6. In diabetic subjects, HbAlc had negative corrections with serum FT3, FT3/FT4 and TSH (P< 0.001), and positive correction with serum FT4 (P< 0.05). After adjustment for age, sex, BMI, HbAlc, ALT, AST, GGT and TSH, the associations between HbAlc and serum FT3, FT3/FT4 and FT4 did not change in type 2 diabetic subjects (P < 0.001).7. Serum FT3 and FT3/FT4 were higher in the non-obese group than those in the overweight and obese group (all P< 0.05), but serum TSH and FT4 had no significant difference between the two groups (all P> 0.05).8. After adjustment for age, sex, SBP, DBP, ALT, GGT, TG, LDL, HDL, FPG and HbAlc:in the non-obese group, BMI had no corrections with serum FT3, FT3/FT4, TSH and FT4 (P= 0.001,0.002,0.047 and -0.095, P> 0.05); in the overweight and obese group, BMI had positive corrections with serum FT3 (β= 0.054, P< 0.001) and FT3/FT4 (β= 0.011, P< 0.001).Conclusions:1. Diabetic patients with uncontrolled glucose are likely to have effects on thyroid hormones, even NTIS. HbAlc is inversely related with serum FT3 and FT3/FT4.2. Obesity has significant effects on serum thyroid hormone levels, and BMI is positively related with serum FT3 and FT3/FT4.