The Correlation Study Between Thyroid Function And Insulin Resistance

Objective: Metabolic syndrome is a clustering of obesity,dyslipidemia,diabetes and hypertension,which can lead to increased risk of atherosclerotic cardiovascular disease.Insulin resistance(IR)is the central pathophysiological phenomenon underlying this clustering.Thyroid hormones play an important role in regulating energy balance,metabolism of glucose and lipids.Thyroid dysfunction can affect metabolism.Hypothyroidism is associated with obesity,dyslipidemia and increased atherosclerotic cardiovascular disease risk.However,the study of association between thyroid function within reference ranges and cardiovascular risk factors is scarce and the results are inconsistent.Therefore,in the present study,we evaluated the relation of IR with thyroid function in euthyroid individuals.Methods: This study was conducted in Health Examination Center of Hebei Province General Hospital from January to April,2015.Eventually,a total of 650 euthyroid individuals were enrolled in the study.Oral glucose tolerance test with a 75 g of glucose load was proceeded in all subjects.Written informed consent was obtained from them.Peripheral venous blood samples were collected from all participants.Serum was obtained by centrifugation at 3,000 rpm for 10 min.Blood glucose,blood lipids and other parameters were analysed by automatic biochemical analyzer.Serum insulin,thyroid hormones and thyroid stimulating hormone were detected by electrochemical luminescence method.Glycated hemoglobin was detected by high performance liquid chromatography.The homeostasis model assessment of insulin resistance(HOMA-IR)was used to evaluate IR,as calculated by the following formula: Fasting glucose(mmol/L)×fasting insulin(mU/L)/22.5.The highest quartile of HOMA-IR was considered the cutoff point for IR,and the subjects were divided into insulin resistance group and the control group.All statistical analyses were performed using SPSS 17.0 software.Results:1 The association of the baseline clinical characteristics and IRWe observed the differences of age,BMI,glucose,lipid levels,thyroid function and other values between the control group and insulin-resistant group.Compared with the control group,the insulin-resistant group had larger BMI and higher WHR(P<0.001).The insulin-resistant group also had higher levels of serum TG,LDL-C,APOB,FBG,PBG and HBA1 c than the control group(P<0.05).Compared with the control group,the insulin-resistant group had lower HDL-C.Furthermore,the insulin-resistant group had increased FINS,2hINS,HOMA-IR than the control group(P<0.001).2 Associations between IR and serum levels of thyroid hormones and thyroid stimulating hormoneWe observed the differences of serum levels of thyroid hormones(total triiodothyronine,total thyroxine)and thyroid stimulating hormone between the control group and insulin-resistant group.Compared with the control group,the levels of total triiodothyronine were lower in insulin-resistant group(P<0.05).However,there were no significant differences in the levels of total thyroxine and thyroid stimulating hormone between the two groups.3 Comparison of serum levels of thyroid hormones and thyroid stimulating hormone between NGT,IGR and T2 DM groupAll subjects were divided into normal glucose tolerance group(NGT),impaired glucose regulation group(IGR)(IGR=impaired fasting glucose(IFG)and impaired glucose tolerance(IGT))and type 2 diabetes mellitus group(T2DM)by the oral glucose tolerance test.We found there was no significance in the levels of total triiodothyronine,total thyroxine and thyroid stimulating hormone among the three groups.4 The association of serum thyroid hormones and thyroid stimulating hormone with related metabolic factorsIn the study,we detected the correlation of serum total triiodothyronine,total thyroxine and thyroid stimulating hormone level with related metabolic factors by Spearman's correlation coefficient.The results showed that serum total triiodothyronine was negatively associated with TC,TG,FINS and HOMR-IR.However,serum thyroid stimulating hormone level was positively correlated with TC,TG and 2hINS.5 The association of serum total triiodothyronine level with the prevalence of IRWe divided all the participants into four groups across total triiodothyronine quartiles(Q1:1.30-1.64nmol/L,Q2:1.65-1.82nmol/L,Q3:1.83-2.04nmol/L and Q4:2.05-3.1nmol/L).From the lowest quartile to the highest quartile of serum total triiodothyronine level,the prevalence of IR were 80.10%,77.40%,75.60% and 66.70%,respectively.Compared with subjects in first quartile,a significant decrease of prevalence of IR was observed in the highest quartile(P=0.013).Compared with quartile 1 of serum total triiodothyronine,univariate logistic regression analysis showed that total triiodothyronine in quartile 4 had a significant correlation with decreased odds of IR.After further adjustment for age,sex,BMI,WHR,TG,TC,LDL-C,HDL-C,HBA1 c,serum total thyroxine and serum thyroid stimulating hormone,the ORs of IR for increasing serum total triiodothyronine quartiles were 1.00(reference),0.71(95%CI: 0.36-1.41),0.77(95%CI: 0.54-1.10)and 0.74(95%C: 0.58-0.94),respectively.6 The association of serum total thyroxine level with the prevalence of IRWe divided all the participants into four groups across total thyroxine quartiles(Q1:66.00-96.63nmol/L,Q2:96.64-107.30nmol/L,Q3:107.31-120.82 nmol/L and Q4:120.83-181.00nmol/L).From the lowest quartile to the highest quartile of serum total thyroxine level,the prevalence of IR were 80.50%,69.80%,76.60% and 73.40%,respectively.Compared with subjects in first quartile,a decrease of prevalence of IR was observed in the second quartile(P=0.047).Compared with quartile 1 of serum total thyroxine,univariate logistic regression analysis showed that the odds ratios of IR prevalence in quartile 2,quartile 3 and quartile 4 were decreased,but the results were not statistically significant.After further adjustment for age,sex,BMI,WHR,TG,TC,LDL-C,HDL-C,HBA1 c,serum total triiodothyronine and serum thyroid stimulating hormone,the ORs of IR for increasing serum total thyroxine quartiles were also decreased,but these were of no significant difference.7 The association of serum thyroid stimulating hormone level with the prevalence of IRWe divided all the participants into four groups across thyroid stimulating hormone quartiles(Q1:0.27-1.36 uIU/ml,Q2: 1.37-1.91uIU/ml,Q3: 1.92-2.71uIU/ml and Q4: 2.72-4.20uIU/ml).From the lowest quartile to the highest quartile of serum thyroid stimulating hormone level,the prevalence of IR were 73.80%,75.00%,74.80% and 76.60%,respectively.Compared with subjects in first quartile,an increase of prevalence of IR was observed in the second,third and highest quartile,but the differences were not statistically significant.Compared with participants in quartile 1 of serum total thyroxine,univariate logistic regression analysis showed that the ORs of IR prevalence in quartile 2,quartile 3 and quartile 4 were increased gradually,but the results were not statistically significant.After further adjustment for age,sex,BMI,WHR,TG,TC,LDL-C,HDL-C,HBA1 c,serum total triiodothyronine and serum total thyroxine,the ORs of IR for increasing serum thyroid stimulating hormone quartiles were also increased,but these were of no significant difference.8 The correlation of IR with related metabolic factorsIR was treated as an independent factor.We detected the correlation of IR with serum levels of total triiodothyronine,total thyroxine and thyroid stimulating hormone,age,sex,BMI,WHR,lipid,HBA1 c by multivariable logistic regression.The results indicated that there was a negative association between IR and HDL-C,serum total triiodothyronine,and a positive association between IR and BMI,TG,LDL-C and HBA1 c.Conclusion: Compared with the control group,the levels of total triiodothyronine were significantly lower in insulin-resistant group among euthyroid individuals.Decrease of total triiodothyronine levels in euthyroid individuals was positively associated with insulin resistance,which was a risk factor of insulin resistance.