Endocrine Abstracts

JOINT1693

Background: 3-phenoxybenzoic acid (3PBA), a metabolite of pyrethroid insecticides, has been linked to alterations in thyroid hormone levels in adults and pregnant women. However, research on 3PBA exposure in children and its interaction with iodine status remains limited. This study examines the relationship between early life 3PBA exposure and childhood thyroid function according to iodine status.

Methods: A total of 439 children aged 6 (231 boys and 208 girls) were included from the Environment and Development of Children cohort. Thyroid function was assessed through serum levels of thyrotropin (TSH), triiodothyronine (T3), and free thyroxine. Urine 3PBA concentrations were measured using morning spot urine samples. Iodine status was categorized based on urinary iodine concentration (UIC) as follows: iodine deficient (< 100 μg/l, n = 19, 4. 3%), adequate (100–199 μg/l, n = 42, 9. 6%), more than adequate (200–299 μg/l, n = 54, 12. 3%), mild excessive (300–999 μg/l, n = 170, 38. 7%), and severe excessive (≥ 1000 μg/l, n = 154, 35. 1%) groups. The association between urinary 3PBA levels and thyroid function was analyzed.

Results: The geographic mean creatinine-adjusted urinary 3PBA concentration was 1. 1 ± 2. 4 mg/g. Higher urinary 3PBA levels were significantly associated with increased serum T3 levels (β=2. 191, SE=1. 096, P-value=0. 046), after adjusting by age, gender, family history of thyroid disease, gestational age, birth weight and second-hand tobacco smoking. UIC group was significant effect modifier on relationship between serum TSH and urinary 3-PBA levels. In iodine-deficient group, urinary 3-PBA levels was positively associated with serum TSH levels (β=0. 51, SE=0. 212, P-value=0. 039). In iodine-excess group, urinary 3-PBA levels was positively associated with serum T3 levels (β=3. 66, SE=1. 831, P-value=0. 047)

Conclusion: Urinary 3PBA concentration was related to thyroid function in 6-year-old children, with iodine status acting as an effect modifier. These findings suggest that both iodine deficiency and excess influence the relationship between pyrethroid exposure and thyroid function in early childhood. Further research is needed to understand the long-term health implications of these interactions.