Relationship between thyroid function and glucose level in adults with subclinical hypothyroidism and euthyroid

Abstract

Objective To investigate the relationship between thyroid function and glucose level in adults with subclinical hypothyroidism and euthyroid. Methods A total of 2751 subjects completed a questionnaire survey and measurement for blood pressure, height, body weight, waist circumference, thyroid stimulating hormone (TSH), free triiodothyronine (FT3), free thyroxine (FT4), fasting plasma glucose (FPG), oral glucose tolerance test (OGTT) 2-h glucose, triglyceride (TG), total cholesterol (TC) and high-density lipoprotein cholesterol (HDL-C). According to the level of thyroid hormone, the subjects were divided into subclinical hypothyroidism group (n=193) and euthyroid group (n=2146). Those in the euthyroid group were further divided into low TSH group (n=352, TSH ≥0.3 to <1.0 mU/L), moderate TSH group (n=916, TSH ≥1.0 to ≤1.9 mU/L) and high TSH group (n=944, TSH 1.9< to ≤4.8 mU/L). According to serum level of glucose, all the subjects were divided into normal glucose tolerance (NGT) group, impaired glucose regulation (IGR) group, and diabetes mellitus (DM) group. The relationship between thyroid function indexes and glucose was analyzed. Student's t test or Analysis of Variance was used for data analysis. Results The level of OGTT 2-h glucose in the subclinical hypothyroidism group was significantly higher than that in the euthyroid group ((8.3±4.4) vs (7.7±4.2) mmol/L, t=-2.163, P<0.05). The level of FT4 in the DM group was significantly higher than that in the IGR group and NGT group ((16.8±2.1), (16.3±2.1), and (16.2±1.9) pmol/L, respectively; F=10.515, P<0.01). The prevalence of subclinical hypothyroidism in the DM group and IGR group was significantly higher than that in the NGT group in females, and the prevalence of subclinical hypothyroidism in females was significantly higher than that in males. After adjusting for body mass index (BMI), waistline, blood pressure and lipids, the level of FPG was positively correlated with FT4 in the total population (β=2.748, P<0.01). For males, the level of FPG was positively correlated with FT4 (β=2.346, P<0.01). The level of OGTT 2-h glucose in females was correlated with FT4 (β=2.748, P<0.01). Within the normal range, the higher level of FT4 showed higher risk of diabetes (total population: odds ratio (OR)=1.142, 95% confidence interval (CI) 1.064 to 1.225, P<0.01; female: OR=1.147, 95% CI 1.024 to 1.284, P<0.05; male: OR=1.142, 95% CI 1.035 to 1.261, P<0.01). There was no correlation between TSH or FT3 and diabetes. Conclusion The prevalence of subclinical hypothyroidism may be increased in female patients with IGR or DM.FT4 could be positively correlated to blood glucose, and higher level of FT4 might result in higher risk of diabetes. Key words: Subclinical hypothyroidism; Thyroid function; Plasma glucose