Salt
The amount of iodine and the specific iodine compound added to salt varies from country to country. In the United States, the Food and Drug Administration (FDA) recommends [21 CFR 101.9 (c)(8)(iv)] 150 micrograms of iodine per day for both men and women. US iodized salt contains 46–77 ppm (parts per million), whereas in the UK the iodine content of iodized salt is recommended to be 10–22 ppm.
Iodine deficiency
It is well known that micronutrient deficiencies change the development of intelligence and iodine is no exception. Lacking in iodine during human development causes a fall, in average, of 12 IQ points in China.