Iodine-supplementation trials.

Iodine deficiency as a major determinant of endemic goiter has been recognized for several decades. The evidence is also strong that iodine supplementation is effective in preventing both varieties of endemic cretinism, provided it is given before conception; early fetal and infant death may also be prevented. However, the reason for the variation in prevalence of the different types of cretinism is still a matter of conjecture. Iodine supplementation may improve motor and cognitive performance, but the evidence needs to be evaluated in light of the difficulty in transposing tests of intellectual and motor ability developed in one culture to another very different one.