Metabolic lipid profiles and thyroid nodule diameter: a retrospective cross-sectional study

Introduction: Thyroid nodules are common endocrine abnormalities, and increasing evidence suggests that metabolic factors may influence their development and growth. Dyslipidemia has been associated with thyroid nodules; however, the relationship between lipid parameters and quantitative nodule characteristics remains unclear. In particular, the association between non–high-density lipoprotein cholesterol (non-HDL-C) and thyroid nodule size has not been sufficiently investigated. Therefore, this study aimed to evaluate the association between serum lipid profile, thyroid-stimulating hormone (TSH) levels, and ultrasonographic characteristics of thyroid nodules, with particular emphasis on nodule diameter.Methods: This retrospective cross-sectional study was conducted at the Internal Medicine outpatient clinics of Elazığ Fethi Sekin City Hospital, between January 2022 and May 2025. The study population consisted of adult patients with at least one ultrasonographically confirmed thyroid nodule and concurrent laboratory measurements. Demographic, biochemical, and ultrasonographic data were retrospectively retrieved from electronic medical records. The largest nodule diameter, number of nodules, and morphology were recorded. Correlation and regression analyses were performed to evaluate associations between lipid parameters and thyroid nodule characteristics.Results: A total of 109 patients (81.7% female, mean age 48.17 ± 12.98 years) were included. Sixty-six patients had solid nodules and 43 had cystic nodules. Lipid parameters and TSH levels did not differ significantly between cystic and solid nodules. Nodule diameter showed weak but statistically significant positive correlations with TC (r = 0.207, p = 0.031), TG (r = 0.221, p = 0.021), and non-HDL-C (r = 0.240, p = 0.012), whereas LDL-C and HDL-C were not significantly correlated. In linear regression analysis using log-transformed diameter, TC (β = 0.029, p = 0.034), TG (β = 0.024, p = 0.010), and non-HDL-C (β = 0.038, p = 0.014) were significantly associated with larger nodule size, corresponding to approximately 2–4% increase in diameter per 10 mg/dL increment. None of the lipid parameters predicted solid versus cystic morphology in logistic regression models.Conclusion: Serum TC, TG, and non-HDL cholesterol were associated with larger thyroid nodule diameter, whereas they were not related to nodule morphology or number. These findings suggest that dyslipidemia may be linked primarily to growth-related characteristics of benign thyroid nodules rather than to their ultrasonographic structure. Larger prospective studies including metabolic and endocrine confounders are needed to clarify whether improving cardiometabolic status may influence the natural history of thyroid nodular disease.