Endemic goitres are due to low dietary intake of iodine (less than 100 microgram per day), seen in high mountainous areas like Himalayas, the Alps, around the Great lakes of North America and Derbyshire district of England. Some endemic goitres are due to substances in the diet (goitrogens) which interfere with the trapping of iodine or the synthesis of thyroxine. These include vegetables of brassica family -- turnips and cabbages.
Rarely acknowledged because of its benign appearance, (enlargement of the thyroid gland), endemic goitre can in fact be deleterious to the wellbeing of large populations, notably due to its consequences: cretinism and endemic deaf-mutism. Politicians have often failed to recognize the gravity of the physical and mental consequences of goitre, and the adverse effects which subclinical hypothyroidism has on general health and productivity.
There are many different causes of goitre: disease; developmental defects; and environmental conditions. Iodine deficiency has dramatic effects on goitre prevalence rates and on endemic cretinism. Other factors involved in the causation of the disease are found in a number of commonly consumed foods: cabbage and other members of the Cruciferae family, turnips, various staple foods (maize, cassava, millet, sweet potatoes, lima beans), onions and garlic, olive oil and other vegetable oils, and milk. Water, too, plays a part in the aetiology of endemic goitre. Significant factors include: industrial pollution or artificial contamination of water by the potent antithyroid disulfides of saturated and unsaturated aliphatic hydrocarbons and phthalates; the antithyroid organochlorines detected in chlorinated effluent from plants treating domestic sewage; and the relationship between the geological composition of watersheds and goitre prevalence - a high prevalence occurring in towns located down-stream from sedimentary deposits (shales and coals) rich in organic matter, and a low prevalence where drinking-water is taken from streams flowing across igneous rocks. The goitrogenic effect of a high calcium intake may be masked in the presence of iodine deficiency. Drinking-water heavily polluted by certain bacteria also makes for a high goitre prevalence.
An estimated one billion people are exposed to the risk of goitre because of a deficiency of iodine, and most of them dwell in the tropical regions of the Third World. There are 400 million in Asia alone (excluding China), of whom 80 million are actually suffering from subclinical hypothyroidism. Schoolchildren living in iodine-deficient areas from a number of countries show impaired school performance and lower intelligence quotients in comparison with matched groups from areas which are not iodine deficient. The prevalence of goitre is higher amongst girls than boys. In northern India, a high degree of apathy, linked with reduced mental function, has been noted in populations living in iodine-deficient areas. This effect is also observed in domestic animals such as dogs. In 1978, in a northern Chinese village there were 1313 people with a goitre rate of 65% with 11.4% cretins, known locally as "the village of idiots". The economic development of the village was retarded -- for example, no truck driver or teacher was available. Girls from other villages did not want to marry and live in the village. After the introduction of iodized salt in 1978, the goitre rate dropped to 4% by 1982. No cretins were born during that period. The attitude of the people greatly changed, their economy improved and average income multiplied tenfold.