Long-Term Endocrine Effects of COVID-19: Thyroid Autoimmunity and New-Onset Type 2 Diabetes at a 4-Year Post-Infection Evaluation

Abstract Background: Endocrine complications are increasingly recognized in post-acute COVID-19, but long-term evidence beyond the early pandemic phase remains limited. This study aimed to evaluate incident type 2 diabetes (T2D) and thyroid autoimmuni-ty four years after acute COVID-19 in previously non-diabetic, thyroid-healthy adults. Methods: We conducted a cross-sectional reassessment of adults hospitalized for COVID-19 between August 2020 and July 2021, of whom 96 completed standardized follow-up from January 2024 to June 2025. Baseline data included acute disease sever-ity, admission glucose, inflammatory markers, imaging, and treatments. Reassessment included fasting glucose, thyroid function, anti-TPO/anti-thyroglobulin antibodies, and thyroid ultrasound. Results: At four years, 26 participants (27.1%) developed in-cident T2D, 40 (41.6%) showed thyroid autoimmunity, and 15 (15.6%) had both condi-tions; overall, 47.9% displayed at least one endocrine sequela. Admission hyperglyce-mia strongly predicted later T2D, and T2D prevalence increased with acute disease severity. Additional risk factors included age ≥60 years, hypertension, and se-vere/critical initial illness. Thyroid autoimmunity was frequent but showed no associ-ations with demographic or acute-phase characteristics. Conclusions: Nearly half of previously healthy adults hospitalized for COVID-19 de-veloped long-term endocrine sequelae. Admission hyperglycemia and acute severity identify individuals at higher risk for future dysglycemia, whereas thyroid autoim-munity appears widespread but severity-independent. Long-term metabolic monitor-ing and thyroid screening are warranted in COVID-19 survivors.