[Is iodination of cooking salt still necessary? Current studies on iodine supply in Switzerland]

Salt with 3.75 mg iodide per kg was introduced in Switzerland stepwise in the individual cantons between 1922 and 1952. The iodide content was raised to 7.5 mg in 1962 and to 15 mg per kg in 1980. 92% of retail salt and 78% of all salt for human consumption (including salt used in industrial food processing) was iodized in 1989. Under this measure, prevalence of grade 1b or larger goiter dropped continuously to a present value of 1.3% in school-children and 0.3% in male army recruits. Endemic cretinism has disappeared completely. Urinary iodine has reached the desired range of 150 +/- 77 (SD) micrograms per g creatinine. The following facts prove that iodization of salt (and not other changes of food habits) have corrected the iodine deficiency in Switzerland: 1. Urinary iodine is highly correlated with urinary sodium. Backward extrapolation yields a theoretical urinary iodine of 30 micrograms per g creatinine in the absence of iodized salt, a value typical of severe deficiency. 2. Goiter prevalence declined later in those cantons which introduced iodized salt last. 3. Surrounding countries without iodized salt (France, Italy, Federal Republic of Germany, Spain) suffer from considerable iodine deficiency with areas of high goiter prevalence and even endemic cretinism. The new data underscore the absolute and continued need for iodized salt in Switzerland.