Comparison of Thyroid Function in Lead Poisoned Patients and Healthy Individuals in North India

Background: Lead remains a pervasive environmental toxicant in India, with emerging evidence linking it to endocrine disruption. Its potential effect on thyroid function remains unclear, with inconsistent findings across studies. This study aimed to evaluate the association between blood lead concentration (BLC) and thyroid hormone levels in a North Indian population. Methods: This retrospective study included 237 patients from Punjab who underwent simultaneous testing for BLC and thyroid hormones between January 2022 and December 2023. Patients were grouped by BLC (<10, 10–25, >25 µg/dL), and those with known thyroid disease or on thyroid-altering medications were excluded. BLC and thyroid hormones (fT3, fT4, TSH) were measured using validated instruments (LeadCare II, Roche Elecsys). Results: Group 3 (BLC >25 µg/dL) had significantly higher fT4 levels (19.26 ± 4.95 pmol/L) and lower TSH levels (2.19 ± 1.77 µIU/L) compared to Group 1 (fT4: 16.26 ± 6.65 pmol/L; TSH: 3.60 ± 4.59 µIU/L; p <0.05). No statistically significant differences were observed in fT3 values between the groups (p = 0.513). Regression analysis showed a positive association between BLC and fT4 and a negative association with TSH. These findings suggest a trend toward subclinical hyperthyroid features in individuals with elevated lead levels. Conclusion: Elevated BLC is associated with altered thyroid function, notably increased fT4 and decreased TSH concentrations, even in the absence of overt thyroid disease. These results support lead’s role as a potential endocrine disruptor, with possible involvement of oxidative stress and neuroendocrine pathways.