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
Fluorine deficiency Fluorine deficiency Fluoride or fluorine deficiency is a disorder which may cause increased dental caries (or tooth decay, is the breakdown of dental tissues by the acidic products released by the "bacterial fermentation of dietary carbohydrates.") and possibly osteoporosis (a bone disorder which leads to a decrease in bone mass, and an increase in bone fragility), due to a lack of fluoride in the diet. In terms of dietary sources, fish and tea are considered natural sources of fluoride, as well as tap water that has been fluoridated. The extent to which the condition truly exists, and its relationship to