Although the body doesn’t demand high doses of iodine for daily function, there is some evidence for its use
For most individuals, dietary intake or supplemental iodine between the recommended dietary allowance and the upper daily limits is adequate. However, there are certain situations in which higher doses of iodine may be appropriate.
Treatment of iodine deficiency
High dosages of a 10% solution of potassium iodide have been safely and effectively used for the prevention of iodine deficiency in children between 7 and 13 years of age in a region where iodine deficiency is endemic. In this setting, dosages of 8.7 mg every 2 weeks or 29.7 mg every month were given. A single oral dose of 570 mg iodine has been shown to resolve the condition of iodine deficiency for up to 6 months without any undesirable effects or alteration of thyroid function tests. Intramuscular injections of iodine have also been used for the treatment of iodine deficiency, with a single dose of 480 mg of iodine resolving this condition for longer than 9 months.
High dosages of iodine have also been studied in the setting of radiation emergencies, due to their ability to reduce the uptake of radioactive iodine. Single doses of 50 mg or 100 mg of potassium iodide were observed to suppress thyroid uptake of radioactive iodine in radiation emergencies by 73.3% and 79.5% respectively at 24 hours.
The thyroid absorption of radioactive iodine is two times greater in individuals with insufficient levels of dietary iodine intake compared to euthyroid adults (having normal thyroid function) with iodine-sufficient diets.
Factors that affect the ability of potassium iodide to block radioactive iodine uptake include the typical dietary intake of iodine and time of administration relative to exposure to radioiodine. The thyroid absorption of radioactive iodine is two times greater in individuals with insufficient levels of dietary iodine intake compared to euthyroid adults (having normal thyroid function) with iodine-sufficient diets. With administration two or eight hours after exposure, the protective effects are 80 and 40% respectively with iodine-sufficient diets, but only 65 and 15% with iodine-deficient diets. Administration 16 hours after exposure will have little or no protective effect, thus, if a radiation emergency is anticipated, emergency kits should contain iodine support in a format intended for ingestion.
Breast and prostate disease
In addition to repletion therapies for iodine deficiency and protection in radiation emergencies, higher doses of iodine have been studied benign breast and prostate conditions including fibrocystic breast disease, cyclic mastalgia, and benign prostatic hyperplasia. Daily dosages of molecular iodine ranging from 1.5 to 6 mg were studied and compared to placebo for the treatment of cyclic mastalgia in euthyroid women for a period of six months. Dosages of 3 or 6 mg were associated with statistically significant improvements in pain, with more than 50% of women in the 6 mg group reporting a clinically significant reduction in overall pain. All dosages were associated with an acceptable safety profile and no dosage-related adverse events were observed.
In addition to repletion therapies for iodine deficiency and protection in radiation emergencies, higher doses of iodine have been studied benign breast and prostate conditions including fibrocystic breast disease, cyclic mastalgia, and benign prostatic hyperplasia.
Supplementation with Lugol’s solution at a dosage of 5 mg/day for a period of 8 months in men with Stage I or II benign prostatic hyperplasia was found to increased urine flow rate and reduce prostate-specific antigen values. High levels of iodine consumption in Japanese populations is associated with a low incidence of both benign and malignant breast and prostate disease, leading to suggestions that iodine intake be increased to at least 3 mg/day in individuals with high risk of such pathology due to the potential antioxidant and apoptotic effects in these tissues.
Potential adverse effects of high iodine intake
Because there are concerns for iodine-induced hypothyroidism or hyperthyroidism when routine daily iodine intake considerably exceeds the upper daily limits, high dose iodine supplementation should only be undertaken with the support of a physician who is aware of the potential adverse effects and performs appropriate labs to rule out risk factors such as thyroid autoimmunity.
Exposure to excess iodine through dietary intake or iodine repletion programs has, at times, been associated with a variety of thyroid dysfunctional states including thyroid autoimmunity, goiter, hypothyroidism, and hyperthyroidism. It is worthy to note however that excess intake of fluoride, chlorine, and bromide, which are molecularly similar to iodine, also is common from water and other sources. These elements have also been documented to have an impact on thyroid function, particularly when in excess.,, The possible contribution of these elements and many other compounds present in the environment were not investigated in these studies.
Exposure to excess iodine through dietary intake or iodine repletion programs has, at times, been associated with a variety of thyroid dysfunctional states including thyroid autoimmunity, goiter, hypothyroidism, and hyperthyroidism.
Iodine-induced goiter and hypothyroidism has been described in individuals in regions with high levels of iodine in their drinking water. In one study, the incidence of goiter was 3.69 times higher in children with urinary iodine >1500 mcg/L than children with urinary iodine levels of 100-199 mcg/L. A cross-sectional study of 2,147 adults in China with iodine intake from various sources (high water levels, adequate diet, or iodized salt supplementation) found that thyroid nodules were more likely to be found in individuals with urinary iodine excess and deficiency, subclinical hypothyroidism was most likely individuals with iodine excess, and subclinical and overt hyperthyroidism was found most often in the iodine deficient group.
A cross-sectional study of 1,085 individuals in Brazil after five years of excessive iodine supplementation (due to high table salt iodine levels) found urinary iodine levels to be elevated (>300 mcg/L) in greater than 45% of individuals. Chronic autoimmune thyroiditis was present in 16.9% of the studied population, affecting women approximately twice as much as men. Previous population studies prior to the higher levels of salt iodine fortification found population median urinary iodine levels of 106 mcg/L and a lower prevalence of chronic autoimmune thyroiditis at 9.4%.
High doses of iodine in excess of the upper daily limits are not recommended for individuals who are pregnant or breastfeeding, although iodine is necessary for the health of both the mother and growing fetus or infant at these times.
Overall, high intake of iodine has been observed to come with the risk of iodine-induced hypo- or hyperthyroidism, particularly in the setting of autoimmunity.,, Iodine-induced hypothyroidism often is transient, and may be a protective response of the body to prevent the production of too much thyroid hormone, which can be far more dangerous. The incidence of hyperthyroidism with iodine repletion in endemic goiter regions is low and is more common in individuals with nodular goiters. High doses of iodine in excess of the upper daily limits are not recommended for individuals who are pregnant or breastfeeding, although iodine is necessary for the health of both the mother and growing fetus or infant at these times.
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