Iodine in biology
The U.S. Food and Nutrition Board and Institute of Medicine recommended daily allowance of iodine ranges from 150 micrograms per day for adult humans to 290 micrograms per day for lactating mothers. However, the thyroid gland needs no more than 70 micrograms per day to synthesize the requisite daily amounts of T4 and T3. The higher recommended daily allowance levels of iodine seem necessary for optimal function of a number of other body systems, including lactating breasts, gastric mucosa, salivary glands, oral mucosa, arterial walls, thymus, epidermis, choroid plexus and cerebrospinal fluid, among others.
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.