Iodine is essential for red and brown algae as well as all invertebrates. The heaviest known essential trace element for humans is iodine (source). Iodine is a member of the halogen family on the periodic table of elements.
A dietary deficiency of iodine is the single most significant cause of preventable brain damage and mental retardation.
A lack of iodine is one of the most common nutritional deficiencies in the world (source).
Mechanism of action
Iodine in combination with the amino acid tyrosine link together to manufacture thyroid hormones. Thyroxine (T4) is much more abundant. However, it is not as biologically active as triiodothyronine (T3). Thyroid hormone speeds up metabolism and increases basal metabolic rate, in addition to controlling the rate of oxygen utilisation and releasing energy from energy-producing nutrients.
When there is inadequate dietary intake, plasma levels of thyroid hormones are reduced and more thyroid stimulating hormones (TSH) is released from the pituitary gland (source). If an iodine deficiency is chronic, the thyroid gland enlarges as an attempt to soak up more iodine to increase thyroid hormones. The glandular response, the stage of disease, and the concentration of thyroid hormones increasing or decreasing is dependant on the amount of iodine present. According to epidemiological studies, the primary consequence of mild to moderate iodine deficiency is hyperthyroidism, which is intricate with symptoms such as cardiac arrhythmia, osteoporosis, and muscle wasting in the elderly (source).
Iodine is a protective antioxidant that can be oxidised to hypoiodite, a potent oxidant involved in the host defence against microorganisms (source).
The availability of iodine in foods is different depending on various regions of the world and their soil levels. Good sources for iodine include saltwater fish, seaweed, dairy products, and eggs.
Iodine can be lost during cooking, possibly as much as 70% (source). Thus, iodised salt should be added after cooking and not before or during.
Absorption of iodine is 100%. The current Recommended Daily Allowance for iodine is 110-150 mcg in adults. The levels are high for those pregnant (220 mcg) and lactating (290 mcg) respectfully (source). Supplementary dosages range between 1,000-10,000 mcg. Prolonged intake of 1,000 mcg may result in toxicosis.
Certain areas of Poland have been classified as being mild to moderately deficient in iodine. Iodine prophylaxis (a preventive protection measure aimed to avoid the health damage of individuals resulting from an accumulation of radioactive iodine in the thyroid in case of nuclear or radiation accident (source)) based only on iodised household table salt that contains 30 mg of potassium iodide per kg of salt has been highly effective (source). If iodised salt is left exposed to the air, that it will slowly lose its iodine content (source).
Many try and mimic the Japanese intake of iodine and depending on their source of information; it could be dangerous. The amount of iodine the Japanese consume daily from seaweeds has previously been estimated as high as 13.5 to 45 mg/day (source, source). Dr Lawrence Wilson suggests that the current RDA is too low and that the ideal dosage of iodine today is much higher, somewhere between 5 and 15 mg daily (source). However, a literature-based analysis estimates that the Japanese iodine intake-- mostly from seaweeds--averages 1,000-3,000 mcg per day or 1-3 mg/day (source). Thus it appears that a daily intake of 2,000 mcg (2 mg) is a safe dosage and non-toxic.
Urinary Iodine test has revived due to the interest and growing realisation of a widespread iodine deficiency (source).
TSH should not be above 3.5, while many physicians use 5 as the upper limit of "normal" (source).
Athletes may require additional iodine as it can be excreted through sweat. Dietary iodine stores could be depleted in an athlete undergoing a regular training regime (source). In one hour of playing soccer, athletes may excrete 52 mcg, and profuse sweating may cause an iodine deficiency. This may suggest that those who have a high workload (such as an athlete), or those which are heat stressed have an increased requirement of iodine (source).
Iodine significantly increased both basal and post-stimulation TSH (source)
Our modern environment is very high in iodine antagonists such as flourine, bromine and chlorine. We quite literally bathe and swim in it! Halogens compete with one another because they look similar at the atomic level and can replace each other (source, source).
Hair Tissue Mineral Analysis Notes:
Hair appears to be a valuable biological indicator tissue for assessing long-term iodine status.
Adequate iodine status corresponds with hair iodine uptake saturation (source).
Mercury and copper toxicity stimulate hormone synthesis. Thyroxine (T4) requires manganese, iodine, tyrosine, cyclic AMP, vitamin C, B-complex and other micronutrients.
Low hair potassium is associated with reduced sensitivity of the mitochondrial receptors to thyroid hormone (source).
Toxicity / Drug interactions:
Excessive intake of iodine will inhibit the synthesis of thyroid hormone which can result in goitre.
In infants, an enlarged thyroid gland may obstruct their airway. It has been shown that high intakes of iodine may contribute to autoimmune hypothyroidism and that Graves’ disease can manifest at a younger age (source). Foods from the Brassica family, such as broccoli, cabbage, and turnips impair utilisation of iodine and increase dietary intake requirements.
Excessive consumption of brominated vegetable oils will deplete iodine levels. It is commonly found in citrus flavoured soda (source).
Nodules are frequently associated with Graves disease in iodine-deficient areas, and the incidence of carcinoma is high in palpable cold nodules. Iodine should be limited for clients that have graves disease. However, they generally need nutrient.
It has been noted in literature that an excess of iodine can react with H202 to form free radicals that cause irreversible thyroid tissue damage (source).
Urinary iodine reflects intake while plasma-bound iodine or thyroxine reflects function.
Deficiency in dietary iodine can cause low thyroid hormone production, and excess can depress thyroid function as well as cause an overactive thyroid.