SN3 SHORT NOTE 5M ★ High-yield

Describe the iodine deficiency disorders with their prevention.

Biochemistry · 1st Professional — Pre-Clinical

Definition

Iodine deficiency disorders (IDD) = the whole spectrum of consequences of iodine deficiency in a population, of which goitre is only the most visible.

Requirement 150 µg/day; 250 µg in pregnancy and lactation
Total body iodine 15–20 mg, most of it in the thyroid

Role of Iodine

Dietary iodide absorbed → Trapped by the thyroid sodium–iodide symporter — concentrated 30× → Oxidised by thyroid peroxidase → Organification — iodinates tyrosine residues on thyroglobulin → MIT and DIT → Coupling: DIT + DIT → T4; MIT + DIT → T3

T4 is the chief secretory product; T3 is the active hormone, formed mostly by peripheral deiodination (a selenium-dependent enzyme)

The Spectrum of Disorders

Age group	Consequences
Fetus	Abortion, stillbirth, congenital anomaly, increased perinatal mortality
Neonate	Neonatal hypothyroidism (cretinism) — irreversible mental retardation, deaf-mutism, spasticity, short stature
Child and adolescent	Goitre, impaired mental function, poor school performance, growth retardation
Adult	Goitre, hypothyroidism, impaired mental function, reduced work capacity

Iodine deficiency is the commonest preventable cause of mental retardation worldwide — the single most important fact about it
Damage to the developing brain is irreversible, which is why prevention must reach women before and during pregnancy

Goitre

↓ Iodine → ↓ T3 and T4 → Loss of negative feedback → ↑ TSH → Thyroid hyperplasia and hypertrophy → goitre

Goitrogens aggravate deficiency — cabbage, cauliflower, tapioca, mustard, soybean, bajra; also thiocyanate from smoking
Tapioca contains cyanogenic glycosides converted to thiocyanate, which competes with iodide uptake

Assessment and Control

Indicator	Significance
Urinary iodine excretion	The best population indicator; adequate if median > 100 µg/L
Goitre prevalence	Endemic if > 5% in schoolchildren
Neonatal TSH	Deficiency if > 3% of newborns have TSH above 5 mIU/L
Serum thyroglobulin	Reflects longer-term status

Universal salt iodisation is the strategy of choice — 15 ppm at consumer level in India
Iodised oil injections or capsules are used where salt distribution is impractical
National Iodine Deficiency Disorders Control Programme in India

Applied Aspects

Iodised salt must be stored dry and added after cooking, since iodine is lost with heat, moisture and light
Jod–Basedow phenomenon — iodine-induced thyrotoxicosis when iodine is given suddenly to a chronically deficient population with nodular goitre
Wolff–Chaikoff effect — a large iodide load transiently inhibits thyroid hormone synthesis; exploited in thyroid storm
Congenital hypothyroidism screening by neonatal TSH is now routine in many Indian centres; treatment within the first two weeks prevents retardation entirely
Selenium deficiency worsens iodine deficiency, because deiodinase requires selenium

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