The effect of subclinical hypothyroidism on insulin resistance and dyslipidemia in obese patients

Objective: The aim of this study is to investigate the effects of subclinical hypothyroidism on dyslipidemia and insulin resistance in obese individuals. Materials and Methods: This retrospective study was conducted using the biochemical and anthropometric data of patients aged 18–65 who were diagnosed with obesity and applied to the Obesity Outpatient Clinic of Tokat Gaziosmanpaşa University Hospital, Department of Family Medicine, between November 2021 and November 2024. Data were obtained through the hospital records and official automation system. Variables analyzed included age, sex, anthropometric measurements (body mass index – BMI), biochemical parameters (fasting serum glucose, insulin, total cholesterol, triglycerides, HDL cholesterol, LDL cholesterol), and thyroid function tests (free T3, free T4, TSH). Patients with conditions that could affect laboratory or anthropometric values (e.g., diabetes mellitus, hyperlipidemia, hyperprolactinemia, congenital adrenal hyperplasia, Cushing's syndrome, hypertension, neoplasms, polycystic ovary syndrome) or those using medications (e.g., insulin sensitizers, oral contraceptives, antiandrogens, statins, aspirin, corticosteroids, GnRH agonists/antagonists) were excluded from the study. Obesity was defined as BMI ≥30 kg/m². Statistical analysis was performed using SPSS version 22.0, and p-values <0.05 were considered statistically significant. Results: A total of 963 patients were evaluated in the study, and 463 patients who met the inclusion criteria were included in the analysis. These patients were categorized into three groups: subclinical hypothyroidism, overt hypothyroidism, and a control group. Among the 463 patients, the prevalence of subclinical hypothyroidism was 3.67%, overt hypothyroidism was 11.45%, and subclinical hyperthyroidism was 0.21%; no cases of overt hyperthyroidism were detected. When 856 patients who solely met the inclusion criteria and were diagnosed with adult obesity were analyzed, the prevalence of subclinical hypothyroidism was found to be 2.8% and the prevalence of overt hypothyroidism was 14.3%. When comparing the overt, subclinical, and control groups, significant differences were found in TSH, total insulin, HOMA-IR, and HDL cholesterol levels. Significant differences were observed between the overt and subclinical groups in total insulin, v HOMA-IR, and HDL cholesterol; between overt and control groups in age, TSH, glucose, total insulin, and HOMA-IR; and between subclinical and control groups only in TSH levels (p<0.005). No significant associations were found between TSH and body mass index (BMI), TSH and HOMA-IR, or TSH and lipid parameters. Moreover, the absence of a correlation between TSH and BMI stands out as a rare finding in the existing literature. When evaluating the average demographic and biochemical parameters by thyroid status: the overt hypothyroidism group had higher mean values for age, TSH, free T4, LDL cholesterol, HDL cholesterol, and total cholesterol; the subclinical hypothyroidism group had higher mean BMI and triglyceride levels; and the control group had higher mean glucose, total insulin, and HOMA-IR levels. Conclusion: Among the 463 obese adults included in our study, the prevalence of subclinical hypothyroidism was found to be 3.67%. No significant association was found between BMI and TSH levels. Furthermore, no statistically significant correlations were observed between serum TSH levels and fasting serum glucose, insulin levels, total cholesterol, triglycerides, HDL cholesterol, LDL cholesterol levels, or HOMA-IR scores. No significant association was identified between subclinical hypothyroidism and insulin resistance or dyslipidemia in obese adults.