Improvement in hearing among otherwise normal schoolchildren in iodine-deficient areas of Guizhou, China, following use of iodized salt.

According to a survey in Guizhou province of China, the average hearing level of otherwise normal schoolchildren in an area of endemic iodine-deficient goitre and cretinism was significantly poorer than in a non-endemic control area. After iodine prophylaxis for three years, audiometric tests showed that the average hearing level had improved and approached that of the non-endemic controls. In addition, mean values for thyroid function tests were restored to within the normal range. It is suggested that the most likely cause of the poorer hearing level among the ostensibly normal schoolchildren in endemic areas is subclinical hypothyroidism due to prolonged severe iodine deficiency.