common type of goitre is endemic goitre, caused by iodine deficiency. Iodine is an essential nutrient that is required for the production of thyroid hormone. When iodine intake is low, thyroid hormone production is low, and in response the pituitary gland secretes greaterquantities of the hormone thyrotropin (thyroid-stimulating hormone.

iodine deficiency, condition in which iodine is insufficient or is not utilized properly. Iodine is an element that directly affects thyroid gland secretions, which themselves to a great extent control heart action, nerve response to stimuli, rate of body growth, and metabolism.

Iodine is essential for normal thyroid hormone production and can be obtained only from the diet. The recommended daily iodine intake is 150 micrograms daily for adults, 220 micrograms daily for pregnant women, and 290 micrograms daily for lactating women. Worldwide, iodine deficiency is the most common cause of thyroid disease. Iodine deficiency is most prevalent in persons living in mountainous areas, where the soil and therefore the food and water contain very small amounts of iodine. In contrast, the condition is least common in persons living in coastal areas, where the soil often contains large amounts of iodine and where iodine-rich seafood is likely to be consumed. It can be prevented by an adequate dietary intake of iodine, which is most often achieved by the addition of iodine to salt.
When iodine intake is low, thyroid hormone production decreases. This results in an increase in thyrotropin secretion by the pituitary gland. Increased thyrotropin secretion stimulates the thyroid to take up more of the iodine that is available, using it to produce thyroid hormone. In addition, thyrotropin stimulates the growth of thyroid cells. Thus, although the compensatory increase in secretion of the hormone acts to minimize the decrease in thyroid hormone production, it also causes enlargement of the thyroid gland, resulting in goitre. Many people with iodine deficiency have only very mild hypothyroidism, which is a decrease in thyroid hormone production that is characterized by symptoms of dry skin, hair loss, a puffy face, weakness, weight increase, fatigue, and mental sluggishness. In very young infants, even a minor degree of hypothyroidism is sufficient to cause intellectual disability. Severe iodine deficiency, particularly during gestation and in the first months following birth, can result in cretinism. Children and adolescents with iodine deficiency typically have diffuse goitre, which will decrease in size if iodine intake is increased. However, in adults the goitre becomes nodular and does not regress when iodine intake is increased.

Prevention of iodine deficiency is most simply accomplished by eating seafood regularly or by using iodized table salt. To overcome natural iodine deficits, government health officials in many countries worldwide have made dietary iodine additives mandatory.

Resource : Britannica.com