Iodine deficiency 15–20 mg of iodine in the human body which is primarily concentrated in thyroid tissue and hormones, but 30% of iodine is distributed in other tissues, including mammary glands, eyes, gastric mucosa, choroid plexus, arterial walls, the cervix, and salivary glands. In the cells of these tissues, iodide enters directly by sodium-iodide symporter (NIS). The diagnostic workup of a suspected iodine deficiency includes signs and symptoms as well as possible risk factors mentioned above. A 24-hour urine iodine collection is a useful medical test, as approximately 90% of ingested iodine is excreted in the urine. For the standardized 24-hour test,
Iodine demonstrated that these animals could survive after eating a 14000 mg/kg dose). Excess iodine can be more cytotoxic in the presence of selenium deficiency. Iodine supplementation in selenium-deficient populations is, in theory, problematic, partly for this reason. The toxicity derives from its oxidizing properties, through which it denaturates proteins (including enzymes). Elemental iodine is also a skin irritant, and direct contact with skin can cause damage and solid iodine crystals should be handled with care. Solutions with high elemental iodine concentration, such as tincture of iodine and Lugol's solution, are capable of causing tissue damage if used in prolonged cleaning