Metabolic maladaptation: individual and social consequences of medical intervention in correcting endemic hypothyroidism

Abstract

Endemic hypothyroidism has been studied in a Central African population in remote Congo (ex-Zaire) to investigate the prevalence, severity, causes, and potential control of this disorder, with questions as to why this disease is conserved, and whether it confers any adaptive advantage in this resource-constrained environment. Iodine deficiency, cassava goiterogens, and selenium deficiency were found to be the factors implicated in the severe hypothyroidism expressed in congenital cretinism and high goiter incidence in this isolated population, which continues to be under observation following medical intervention. Profound hypothyroidism was encountered in whole village populations as measured by serum thyrotropin determinations ranging from very high to over 1000 IU, and thyroxin levels ranging from low to undetectable; cretinism rates were as high as 11% and goiter incidence approached 100%. Assessment of endocrinologic status, caloric requirement, energy output, fertility, and ecologic factors was carried out before and during iodine repletion by depot injection. Hypothyroidism was corrected and cretinism eliminated in the treatment group, with goiters reduced in most instances (with regrowth exhibited in some who escaped control) and some symptomatic goiter patients were offered surgical treatment for respiratory obstruction. Individual patient benefits, including improved strength and increased energy output, were remarkable. The social and developmental consequences observed within the collective groups of treated patients were remarkable for an increase in caloric requirement and a dramatic increase in fertility that led to quantitative as well as qualitative increases in resource consumption. Micronutrient iodine repletion was not accompanied by any concomitant increase in macronutrient supply, and hunger and environmental degradation resulted. The highly prevalent disease of hypothyroidism is found in highest incidence in areas of greatest resource constraint. It may be that hypothyroidism is conserved in such areas because it may confer adaptive advantage in such marginal environments as an effect, as well as a cause, of underdevelopment. Hypothyroidism may limit energy requirements, fertility, and consumer population pressure in closed ecosystems that could otherwise be outstripped. Single factor intervention in a vertical health care program not sensitive to the fragile biologic balance and not part of a culture-sensitive development program might result in medical maladaptation.