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Severe Iodine Deficiency and natural Goitrogens

المؤلف:  Wass, J. A. H., Arlt, W., & Semple, R. K. (Eds.).

المصدر:  Oxford Textbook of Endocrinology and Diabetes

الجزء والصفحة:  3rd edition , p545

2026-05-04

367

Environmental iodine deficiency is common in many areas throughout the world, particularly in inland mountainous areas. Goitre is the most common disorder due to iodine deficiency and its prevalence is inversely related to the median iodine intake of the population. Endemic goitre is usually not associated with hypothyroidism. However, the pattern of circulating thyroid hormones in the population from areas of severe iodine deficiency differs from that found in iodine- sufficient areas. The mean serum T4 is reduced while serum T3 is unchanged or increased and an inverse correlation between serum TSH and T4 is found. The low iodine content within the thyroid gland and the increased TSH stimulation lead to preferential secretion of T3, which is far more potent than T4 in terms of metabolic responses. Thus, the relative increase in T3 secretion enables a patient to maintain the euthyroid status in spite of reduced availability of iodide.

Cretinism is the result of an insufficient supply of thyroid hormones to fetal tissues and is due to severe iodine deficiency in both the mother and the fetus during early stages of gestation. Fetal hypothyroidism is not compensated by transplacental passage of maternal T4 and is responsible for severe physical and neurological damage.

Adult hypothyroidism may occur in rural populations living in areas of severe iodine deficiency where isolation prevents access to iodine- rich foodstuff. In this case, hypothyroidism is rapidly re versed by iodine supplementation. Consumption of food containing antithyroid agents, such as thiocyanate in cassava meal and flavonoids in a variety of plants, may aggravate the effects of dietary iodine deficiency and add to the development of goitre and hypothyroidism. Phloroglucinol, a potent antithyroid compound contained in some species of seaweeds, may play an additional role to that of iodine excess in the development of iodine- induced hypothyroidism.

Acquired hypothyroidism has been described in children on chronic parenteral nutrition as a consequence of the lack of iodine in delivered nutrients [28]. More recently, attention has been focused on environmental endocrine disrupters (pesticides and industrial pollutants) as a possible cause of thyroid imbalance, but their effects on human thyroid function have not been fully elucidated.