Legal augmentation of iodine content in table salt from 10 to 20 mg KI/kg: documented effects a decade later.

In this brief review I have tried to gather all relevant data that have been published, concerning the long-term effects of the statutory requirement by Austrian authorities in 1990 to augment the iodine content of table salt from 10 mg KI/kg table salt to 20 mg KI/kg. Most of the available studies have a selection bias, studying persons referred to hospital for different reasons. Only studies on school children investigate more random samples of the population. However, in spite of the fact that iodine deficiency does not seem to be eradicated completely by this measure, some tendencies have become apparent. The positive tendencies are: (1) thyroid volume in school children has shrunk in comparison to (historical) data before 1990--leading to lack of goitre in this age group; (2) the expected rise in the incidence of thyrotoxicosis was only transient and not very pronounced--indeed thyrotoxicosis seems to have become rarer now than before; (3) the phenotype of thyroid cancer has changed towards the more benign variants. Negative trends described since 1990 are (1) a small increase in the overall incidence of thyroid cancer (possibly due to better diagnostic tools), and (2) a relative rise of autoimmune thyroid disease. All these tendencies await their substantiation by a nationwide survey that is based on strong epidemiological criteria.