S. Yaghi1, C. Ardis1, M.H. Hussein2, L. Tran3, A. Abdelmaksoud4, R. Elshazli5, H. Patel6, H. Aiash3, E. Toraih5 1Tulane University School Of Medicine, New Orleans, LA, USA 2Ochsner Clinic Foundation, New Orleans, LOUISIANA, USA 3SUNY Upstate Medical University, Syracuse, NEW YORK, USA 4University of California, Riverside, Internal Medicine, Riverside, CALIFORNIA, USA 5Tulane University School Of Medicine, Surgery, New Orleans, LA, USA 6Louisiana State University Health Sciences Center, New Orleans, LA, USA
Introduction: Selenium supplementation has been suggested as a potential therapeutic option for Hashimoto's thyroiditis due to its role in thyroid hormone synthesis and metabolism. However, its effects on thyroid function, autoimmunity, and related outcomes remain unclear. This study aims to evaluate the long-term effects of selenium supplementation in patients with Hashimoto's thyroiditis on thyroid function, autoimmune comorbidities, and overall mortality.
Methods: This large-scale retrospective cohort study utilized data from a global federated health research network to compare patients with Hashimoto's thyroiditis who received selenium supplementation after diagnosis (n=2,347) to those who did not (n=2,347). Propensity score matching was employed to balance the groups. Primary outcomes included changes in thyroid function tests, while secondary outcomes included the risk of developing concomitant autoimmune diseases and thyroid cancer.
Results: Selenium supplementation was associated with higher proportions of patients with elevated thyroid peroxidase antibodies (TPOAb) and consistently higher mean levels of free thyroxine (T4), TPOAb, and thyroid-stimulating hormone (TSH) compared to the control group over the 5-year study period. The proportion of patients with elevated TPOAb (>35 IU/mL) was significantly higher in the selenium-treated group at 3 years (6.9% vs. 5.03%, p=0.007), 5 years (7.93% vs. 5.28%, p<0.001), and overall (9.08% vs. 5.92%, p<0.001). The incidence of new concomitant autoimmune disorders was significantly higher in the selenium-treated group compared to the control group (13.59% vs. 10.23%, p<0.001), with a relative risk of 1.33 (95% CI: 1.14-1.56). Specifically, the incidence of Sjögren's syndrome (2.13% vs. 1.32%, p=0.033) and psoriasis (1.83% vs. 0.68%, p<0.001) was significantly higher in the selenium-treated group. The relative risk was 1.61 (95% CI: 1.034-2.515) for Sjögren's syndrome and 2.69 (95% CI: 1.518-4.757) for psoriasis. No significant differences were observed in the incidence of thyroid cancer (0.43% vs. 0.55%, p=0.53) or thyroidectomy (0.64% vs. 0.43%, p=0.32) between the selenium-treated and control groups. However, the risk of all-cause mortality was significantly higher in the selenium-treated group at 5 years (2.94% vs. 1.79%, p=0.009, HR=1.38, 95% CI: 1.09-2.03) and overall (4.77% vs. 2.43%, p<0.001, HR=1.63, 95% CI: 1.18-2.24).
Conclusion: Selenium supplementation in patients with Hashimoto's thyroiditis was associated with higher levels of TPOAb, T4, and TSH, an increased incidence of autoimmune disorders, and a higher risk of all-cause mortality compared to the control group. These findings challenge the use of selenium supplementation as a therapeutic option and highlight the need for further research to confirm these results and investigate the potential mechanisms underlying the observed associated adverse outcomes with selenium supplementation.