Introduction: Nitrate and nitrite are prevalent drinking water contaminants that can interfere with iodine uptake and thyroid hormone synthesis, acting as potential endocrine disruptors. Chronic exposure, even at concentrations within international safety limits, has been linked to autoimmune thyroid disorders. This study aimed to assess the association between drinking water nitrate and nitrite levels and serum thyroid autoantibodies—thyroid peroxidase antibody (TPOAb) and thyroglobulin antibody (TGAb)—in patients with hypothyroidism.
Methods: This cross-sectional study analyzed data from 2015 to 2019, integrating water quality records from the Fars Water and Wastewater Company and clinical data from hypothyroid patients attending the Jahrom endocrinology clinic. Serum TPOAb and TGAb levels were measured using chemiluminescent and ELISA methods, respectively.
Results: A total of 32 hypothyroid patients (9 males, 23 females; mean age 33.2 ± 9.9 years) were included. Median TPOAb and TGAb levels were 297.9 and 41.1 IU/mL, respectively. The median nitrate and nitrite concentrations in drinking water were 25.1 and 0.02 mg/L, both within the WHO limits. A significant positive correlation was observed between nitrate levels and TPOAb concentrations (r = 0.714, P = 0.001), whereas no significant correlation was found between nitrite and TPOAb concentrations.
Conclusion: The findings suggest that long-term exposure to nitrate, even below regulatory limits, may contribute to autoimmune thyroid activation in hypothyroid patients. Continuous monitoring of nitrate in drinking water and future population-based, longitudinal studies are warranted to clarify causal mechanisms and inform public health interventions.