The reasoning: iodine deficiency disorders (IDD)
Requirement: adults 150 µg/day; pregnancy and lactation 250 µg/day; children 90–120 µg/day. Spectrum (Hetzel): fetus (abortion, stillbirth, congenital anomalies, endemic cretinism: neurological with deaf‑mutism, spastic diplegia, squint; myxoedematous), neonate (neonatal hypothyroidism), child/adolescent (goitre, impaired mental and physical development), adult (goitre, hypothyroidism, impaired mental function, iodine‑induced hyperthyroidism after supplementation). The largest population effect is a shift in IQ (≈ 10–15 points) across whole communities.