Iodine deficiency today remains one of the world's most prevalent medical problems, despite years of effort to correct the problem through salt iodination or iodinated oil injections. Reduction of dietary iodine intake below the minimum daily requirement leads to reduced thyroid hormone production and a compensatory increase in TSH secretion. There is preferential secretion of T3 rather than T4. The frequency of goitre and of the occurrence of hypothyroidism is related to the degree of iodine deficiency. In areas of moderate endemic deficiency with urinary iodide excretion between 25 and 50┬╡g/g creatinine, the prevalence of goitre is twenty to fifty per cent, but almost all individuals will be euthyroid. In areas with urinary iodide less than 25┬╡g/g creatinine, as in the Andes, Himalayas, and Central Africa, goitre prevalence may be greater than fifty per cent, and some individuals in such communities are hypothyroid.
