Progress in understanding the clinical consequences of endemic iodine deficiency

Abstract

A diet deficient in iodine may cause a wide spectrum of illness, collectively termed iodine deficiency disorders (IDDs), that affects people of all ages, but particularly pregnant women, the developing fetus, and the neonate. One thousand million people worldwide are potentially at risk from IDD. Endemic goiter is the most common of these disorders, and its prevalence rises commensurate with the degree of iodine lack, reaching 100% in communities with severe iodine deficiency. Despite the highly visible nature of this condition, the major public health problem attributable to iodine deficiency is its detrimental effects on the developing fetal and neonatal brain. This is expressed clinically in its extreme manifestation as endemic cretinism, a disorder of profound mental and physical disability. Nonetheless, lesser degrees of iodine deficiency, by its effects on maternal-fetal thyroid homeostasis, may also impair brain development, commonly presenting as a generalized reduction in the intellectual potential of a community. All IDDs are preventable. Nevertheless, although the benefits of iodine supplementation were recognized as early as 1816 and iodine supplementation programs have been implemented in various countries since 1924, IDDs remain a significant world health problem. Although the technology and methods of implementation of iodine supplementation programs are relatively simple, the monitoring and assessment of such programs are more difficult. The application of thyroid ultrasonography as a measure of thyroid size and monitoring of neonatal thyroid-stimulating hormone levels have introduced new epidemiologic methods to assess the burden of iodine deficiency on the community.