Adiposity Is Associated with a Higher Risk of Thyroid Malignancy in Patients with Hashimoto’s Thyroiditis

<b>Background/Objectives</b>: Both adiposity and Hashimoto's thyroiditis (HT) are states of chronic inflammation. Adiposity may increase the risk of thyroid nodules and thyroid carcinoma. However, its role in patients with HT remains unclear. The connections among thyroid nodularity, adiposity, and HT have not been explored. <b>Aim</b>: To investigate the impact of adiposity on thyroid nodularity in patients with HΤ and to determine whether there are any differences in the risk for thyroid cancer. <b>Methods</b>: This retrospective cohort study included 294 consecutive patients with HT who were categorized according to their body mass index (BMI). Grayscale ultrasound (US) and fine-needle aspiration (FNA) cytology results were evaluated in association with clinicopathological characteristics. <b>Results</b>: After controlling for age and gender, nodules from patients with a BMI ≥ 25 kg/m² showed significantly more suspicious or malignant cytology (Thy 4-5) compared to patients with a BMI < 25 kg/m² (27.03% vs. 18.18%; <i>p</i> < 0.01). Although not statistically significant after adjustments, patients with BMI ≥ 25 kg/m² demonstrated a higher proportion of nodules classified as highly suspicious on ultrasound (28.20% vs. 22.46%). Additionally, overweight and obese patients tended to have more thyroid nodules (mean ± SD: 2.91 ± 2.11) than normal-weight patients (2.36 ± 1.79), a difference approaching marginal significance (<i>p</i> = 0.06). <b>Conclusions</b>: Adiposity is associated with more suspicious and malignant cytology in patients with HT. Overweight and obese patients with HT tended to have more thyroid nodules. Further studies are needed to investigate the mechanisms linking obesity, thyroid nodules, and HT.