Academic journal article The Geographical Review

The Iodine Factor in Health and Evolution

Academic journal article The Geographical Review

The Iodine Factor in Health and Evolution

Article excerpt

The medical geography of iodine deficiency disorders (IDD) makes for fascinating science, but consider first its human dimensions: A baby is born as perfect as any other. During her infancy her parents gradually notice a hoarse cry, a protruding tongue, a too-large head with a sloping forehead, a slumping curve in the tiny spine. For the rest of her life, she will be physically deformed and mentally retarded, her joints will ache, her neck will be dis figured by goiter, and she may experience deafness, tremors, and other neurological disorders. For want of iodine, an otherwise healthy child has become, in proper medical terminology, a cretin,(1) afflicted by cretinism - the appalling condition that gave our language its most offensive slang term for idiocy.

Westerners typically assume that the problem of IDD was solved early in the twentieth century through the universal distribution of iodized salt. Yet today more than a billion people remain at risk worldwide, hundreds of millions suffer from goiter and diminished mental capacity, and millions suffer from cretinism. Although the physiological roots of such an extreme dependency surely must reach to the foundations of human evolution (Dobson 1995), they are neglected in evolutionary theory. In this article I describe the syndromes and causes of IDD, address the medical geography of IDD both modern and ancient, and explore the implications for human evolution.

IDD PATHOLOGY IN MODERN HUMANS

Our species, Homo sapiens sapiens, is extraordinarily dependent on iodine. Modern humans without an adequate, continual supply of the element typically suffer from goiter and cretinism. Goiter is an enlargement of the thyroid gland caused by dietary iodine deficiency. Cretinism is a more severe pathological condition involving physical deformity and mental retardation caused either by dietary iodine deficiency or by malfunction or absence of the thyroid glands that normally process iodine into thyroid hormone. The form caused by dietary deficiency is called endemic cretinism, and that caused by malfunction or absence of thyroid glands is called sporadic cretinism (or congenital hypothyroidism if onset is prenatal). In a European context, Ernst Finkbeiner further categorized endemic cretinism as either gracile or massive forms with substantially different skeletal morphologies (1923). In 1995 Harold D. Foster wrote: "This is not a single disease but rather a syndrome of great diversity which ranges from severe hypothyroidism to major neurological disorder, with many intermediate gradations" (p. 139). Cretinism is diagnosed not by a single, rigid set of traits but by numerous symptoms that vary according to the fetal stage or age of the individual at their onset, to the severity and duration of iodine deficiency, and to geographical location (Pharoah and others 1980). The principal difficulty is in making a reliable diagnosis of cretinism, given its diverse symptoms, the inadequate and confusing medical descriptions inherited from the 1800s and early 1900s when cretinism was common in Europe, and the complex interactions between iodine and selenium (Foster 1995).

Specific syndromes of cretinism include Kocker-Debre-Semelaigne (KDS) and Brissaud infantilism. KDS is defined as "large muscle syndrome. . . . Apparent muscular hypertrophy in hypothyroid children [gives] them the 'herculean' (prizefighter, athletic, or pseudo-athletic) appearance. Associated disorders may include retarded physical and mental development, delayed dentition, . . . peculiar facies, . . . and increased muscle mass" (Jablonski 1991, 180). KDS occurs in both children and adults (Magalini and Scrascia 1981, 456). Brissaud in fantilism syndrome is defined as "mental deficiency, dwarfism with disproportionately long trunk in relation to legs, epiphyseal dysgenesis, large head, delayed closure of the fontanelles, broad nose with wide flaring nostrils, open mouth, coarse facies, . . …

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