Iodine Nutritional Status and Thyroid Autoimmunity in Chinese Children and Adolescents Aged 6-17 Years

Background: Thyroid autoimmunity (TAI), marked by thyroid peroxidase antibodies (TPOAb) and thyroglobulin antibodies (TgAb), affects over 10% of the general population, with children and adolescents experiencing significant impacts on growth and quality of life despite lower prevalence rates compared to adults. Methods: In the context of over 20 years of universal salt iodization (USI) in China, this study investigated the relationship between iodine nutritional status and TAI in children and adolescents aged 6-17. Results: Our findings suggest that while iodine levels are generally sufficient (median urinary iodine concentration [UIC] was 205.2 µg/L), TAI remains a significant concern due to its potential impact on growth and development. TAI was significantly associated with age, sex, and urban-rural residency (p < 0.05). Positive TPOAb and TgAb were identified as risk factors for subclinical hypothyroidism (OR = 2.274, 95% CI: 1.171-1.916). Although some literature suggests that excessive iodine may exacerbate TAI and others propose iodine deficiency as a risk factor, this study did not find a significant overall association between iodine status and TAI. Notably, a low urinary iodine-to-creatinine ratio (UI/Cr) level was linked to an increased risk of TgAb positivity in males (OR = 3.470, 95% CI: 1.200-10.036). In individuals with negative thyroid antibodies, increased BMI (OR = 1.062, 95% CI: 1.032-1.093) and high UI/Cr levels (OR = 1.510, 95% CI: 1.175-1.941) were risk factors for subclinical hypothyroidism, whereas older age (OR = 0.710, 95% CI: 0.555-0.908 for the age 9-11 group; OR = 0.681, 95% CI = 0.484-0.959 for the age 12-17 group) and high UIC levels (OR = 0.739, 95% CI: 0.554-0.985) were associated with reduced risk. No significant associations were observed in the thyroid antibody-positive group. Conclusions: These results highlight the importance of considering individual TAI status when devising iodine supplementation policies.