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.
Nuclear Regulation Authority
On 19 July 2013, the NRA updated its guidelines for the distribution and use of stabilized iodine tablets. Under the old rules designed in 2002 by the former regulator, the NSA, iodine tablets were recommended for those up to the age of 40. These former guidelines were based on studies done on the health of the atomic bomb survivors of Nagasaki and Hiroshima. Later studies however showed that although older people had less risk of developing cancer, the risk was not zero. Therefore, the age limit of 40 was abandoned. Because tablets were needed for approximately 4.8 million people who live within 30 kilometers of a nuclear reactor, implementation may take some time with only one pharmaceutical firm in Japan available for the production. Distribution would be started soon, and local governments were ordered to hold briefings for their residents. The NRA also warned that the use of iodine tablets could cause hypothyroidism, a slow-functioning thyroid gland.