Even with a shelter, there is a chance of exposure to radiation. There is no medicine to prevent radiation from damaging the human body cells. The thyroid gland is especially susceptible to radiation. Normally, your thyroid absorbs iodine, but it has a set level of iodine that it can store. Certain forms of iodine help your thyroid work right.
Most people can get enough iodide from iodized salt or fish in their regular diet.
During exposure to nuclear fallout, radioactive iodine can also be absorbed into the thyroid. Small amounts of radiation in the thyroid will eventually give a large radiation dose to other cells. This can result in loss of the thyroid functions, and even thyroid cancer. The effects of this exposure may not show up for many years. Eating and drinking fallout contaminated water and food increases the retention of radioactive iodine in the thyroid.