Iodine in biology damage). In areas where there is little iodine in the diet, typically remote inland areas and semi-arid equatorial climates where no marine foods are eaten, iodine deficiency also gives rise to hypothyroidism, the most serious symptoms of which are epidemic goitre (swelling of the thyroid gland), extreme fatigue, mental slowing, depression, weight gain, and low basal body temperatures. The addition of iodine to table salt (so-called iodized salt) has largely eliminated the most severe consequences of iodine deficiency in wealthier nations, but deficiency remains a serious public health problem in the developing world. Iodine deficiency is also a problem in
Isotopes of iodine other form of direct radiation). The protective effect of KI lasts approximately 24 hours, so must be dosed daily until a risk of significant exposure to radioiodines from fission products no longer exists. Iodine-131 (the most common radioiodine contaminant in fallout) also decays relatively rapidly with a half-life of eight days, so that 99.95% of the original radioiodine has vanished after three months. Isotopes of iodine There are 37 known isotopes of iodine (I) from I to I; all undergo radioactive decay except I, which is stable. Iodine is thus a monoisotopic element. Its longest-lived radioactive isotope, I, has a