Iodine - The Next Vitamin D ?

Iodine: the Next Vitamin D?

by Lara Pizzorno, MDiv, MA, LMT

Part I: Americans at High Risk for Iodine Insufficiency (*Note Link to Part II Here)

Abstract
Despite the widely held assumption that Americans are iodine-sufficient due to the availability of iodized salt, the U.S. population is actually at high risk for iodine insufficiency. Iodine intake has been decreasing in the U.S. since the early 70s as a result of changes in Americans' food and dietary habits, including the facts that iodized salt is infrequently used in restaurant and processed foods, and iodized salt sold for home use may provide far less than the amount of iodine listed on the container's label. The widespread dispersal of perchlorate, nitrate and thiocyanate (competitive inhibitors of iodide uptake) in the environment blocks absorption of the little iodine Americans do consume, further compounding the problem.

In adults, iodine is necessary not only for the production of thyroid hormones, thus affecting systemic metabolism, but is now recognized to play a protective role against fibrocystic breast disease and breast cancer. In addition, a relationship has been hypothesized between iodine deficiency and a number of other health issues including other malignancies, obesity, attention deficit hyperactivity disorder (ADHD), psychiatric disorders, and fibromyalgia.

Analogous to the case of vitamin D, a nutrient for which the 400 IU RDI, although capable of preventing rickets, has been proven inadequate for this pro-hormone's numerous other functions in the body, the iodine RDI for adults of 150 mcg/day (220 mcg/day for pregnant women), while sufficient to prevent goiter (and cretinism), is inadequate for the promotion of optimal fetal brain development or optimal health in adults. Intake of 3-6 mg/day, an amount commonly consumed in Japan without increased incidence of autoimmune thyroiditis or hypothyroidism, may be necessary to support not only thyroid hormone production, but iodine's important antioxidant functions in the breast and other tissues in which this trace mineral is concentrated.

Part I of this article discusses the numerous factors that place Americans at high risk for iodine insufficiency. Part II reviews iodine's roles in the body, the relationship of iodine insufficiency to the above mentioned pathologies, available options in laboratory assessments of iodine levels, optimal intake, preferential forms of supplementation, and cofactors necessary for optimal iodine utilization.

Introduction

Iodine deficiency, defined as urinary iodine excretion <100 1 ="/-" mg =" typical">10 mg/L, the federal maximum contaminant level. Two million families are estimated to drink water from private wells that fail to meet the federal drinking-water standard for nitrate. In urban areas, municipal wastewater-treatment discharges on surrounding farmland aggravate the problem.36 Hypertrophy of the thyroid gland has been noted at nitrate levels exceeding 50 mg/L. School children living in a community in Slovakia, where drinking-water wells contained high nitrate levels (>50 mg/L), were found to have enlarged thyroid glands and signs of subclinical thyroid disorder (thyroid hypoechogenicity37 [low intensity echoes] by ultrasound [seen in Hashimoto's thyroiditis and Graves disease], increased TSH levels, positive thyroperoxidase antibodies).38

Dietary thiocyanate also inhibits iodine uptake by the NIS. Brassica family vegetables contain compounds that can be converted to thiocyanates in the gut; however, cooking reduces the thiocyanate (and nitrate) content of vegetables, plus only about 50% of the thiocyanate produced in the gut is bioavailable. Cigarette smoking, however, is a significant source of thiocyanate in the body. Recent studies in the U.S. have found that thiocyanate concentrations in the breast milk of smokers were fourfold higher than those of non-smokers, and iodine content in the breast milk of smoking mothers was twofold reduced, likely due to the thiocyanate's competitive inhibition for NIS in the mammary gland. Thiocyanate has a half-life of approximately 6 days, compared to 8 and 5 hours for perchlorate and nitrate respectively.35
Lastly, research suggests a synergistic effect of perchlorate with thiocyanate resulting in significantly more damage to thyroid function than either compound alone in iodine-deficient individuals. Data from the 2001-2002 NHANES revealed that in women with urinary iodine levels <100 mcg/L, the association between perchlorate and decreased T4 was 66% greater than in non-smokers. These results suggest that thiocyanate in cigarette smoke interacts with perchlorate at commonly occurring perchlorate exposures to negatively impact thyroid function to a much greater degree in individuals with urinary iodine levels <100 mcg/L.39 Little or no data are available on the daily-required dose of dietary iodine to withstand inhibition of NIS iodine—uptake by perchlorate, nitrate and thiocyanate present in American's drinking water, food and exposure to cigarette smoke.35

Conclusion
The combination of changes in food production and American dietary habits have significantly decreased iodine consumption in the U.S. The majority of Americans may not even be meeting RDI recommendations for iodine, which given our unremitting, widespread, and increasing exposure to a variety of iodine uptake inhibitors, are likely insufficient for the promotion of optimal brain development or adult thyroid function.

In adults, iodine is necessary not only for the production of thyroid hormones, but has recently been recognized to play a protective role against fibrocystic breast disease and breast cancer. A relationship has also been suggested between iodine deficiency and a number of other health issues including other cancers, obesity, attention deficit hyperactivity disorder (ADHD), psychiatric disorders, and fibromyalgia.

Part II of this article will suggest revising the RDIs to levels that consider these factors and are based on our recently developed understanding of iodine's varied roles in the body and the relationship of iodine insufficiency to the above mentioned pathologies. Available options in laboratory assessments of iodine levels, preferential forms of iodine supplementation, and cofactors necessary for optimal iodine utilization will also be discussed.

Read Part II: Iodine: the Next Vitamin D? Not Just for Thyroid

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