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 among individuals recovering from COVID-19. However, despite growing research, long-term evidence beyond the early pandemic phase remains limited. This study evaluated the 4-year incidence of type 2 diabetes (T2D) and thyroid autoimmunity in adults previously hospitalized for COVID-19 who had no known metabolic or thyroid disorders at baseline. Methods: We performed a cross-sectional reassessment of adults hospitalized for COVID-19 between August 2020 and July 2021. A total of 96 participants completed standardized follow-up between January 2024 and June 2025. Baseline variables included acute COVID-19 severity, admission glucose, inflammatory markers, imaging findings, and therapies received. Reassessments included fasting glucose, thyroid function tests, anti-TPO and anti-thyroglobulin antibodies, and thyroid ultrasonography. Results: Four years after infection, 26 participants (27.1%) had developed incident T2D, 40 (41.6%) exhibited thyroid autoimmunity, and 15 (15.6%) presented with both conditions. Overall, 47.9% displayed at least one endocrine sequela. Admission hyperglycemia was a strong predictor of subsequent T2D (OR 6.67; 95% CI: 1.45–30.58), and T2D prevalence increased proportionally with the severity of the initial infection. Additional risk factors included age ≥60 years, hypertension, and severe/critical acute illness. Thyroid autoimmunity was frequent but did not vary significantly across severity categories. Conclusions: Nearly half (47,9%) of previously healthy adults hospitalized for COVID-19 developed long-term endocrine sequelae. Admission hyperglycemia and acute disease severity identify individuals at increased risk for future dysglycemia, whereas thyroid autoimmunity appears prevalent but independent of initial disease severity. These findings support the need for long-term metabolic monitoring and thyroid evaluation in COVID-19 survivors.