Iodine nutrition, thyroid function, and thyroid autoimmunity four decades after Universal Salt Iodisation in India: a cross-sectional study among schoolchildren (ICMR-SALT-T 1)

Background Epidemiological studies undertaken following the first and second decade after the introduction of Universal salt iodisation (USI) in 1986 had pointed towards mild persistence in goitre, iodine excess as measured by spot urinary iodine concentration (UIC) and increase in thyroid autoimmunity. We aim to look at the status of iodine nutrition, goitre prevalence, thyroid dysfunction, and autoimmunity in Indian school-children in the fourth decade of implementation of USI. Methods 8903 school children aged 10–18 years from eight centres across India were assessed for goitre by physical examination, thyroid function (n = 5512), autoantibody status (n = 5726), iodine nutrition by spot urinary iodine concentration (n = 1853). Findings Overall goitre prevalence was 10.3% (95% CI 9.7%–11.0%), majority (98.6%) being grade I goitre. Female sex (aOR 2.1, 95% CI 1.7–2.5; p < 0.001), obesity (aOR 1.3, 95% CI 1.0–1.6; p=0.03) and anti-TPO positivity (aOR 2.5, 95% CI 1.9–3.1; p < 0.001) were associated with higher odds of goitre. Subclinical hypothyroidism (SCH) was observed in 13% (95% CI 12.2%–14.0%) of children with female sex (aOR 0.8, 95% CI 0.7–0.9; p=0.03) and age (>15 year vs. 10–15 year aOR 0.7, 95% CI 0.6–0.9; p=0.001) associated with lower odds; and overweight (aOR 1.4, 95% CI 1.0–1.8; p=0.03)/obesity (aOR 1.9, 95% CI 1.5–2.3; p < 0.001) and autoantibody positivity with higher odds. Anti-TPO positivity was seen in 10.4% (95% CI 9.5%–11.1%) with higher odds in females (aOR 2.1, 95% CI 1.7–2.5; p < 0.001). Socioeconomic status was not associated with goitre, SCH or autoantibody positivity. MUIC was 133.2 μg/L (IQR-90.62 μg/L −199.49 μg/L). More than 90% of the surveyed household reported use of iodised salt and 89% of the 1615 salt samples tested contained iodine more than 15 ppm. Interpretation Goitre prevalence in India is showing a steady decline, with no difference based on socio-economic background reported in previous studies, indicating positive long term impact of USI. High rates of thyroid autoimmunity and thyroid dysfunction need future follow up studies.