Iodine is an essential element for human health and widely required in biological functions. Iodine is a central component of thyroid gland hormones but also plays an important role in the regulation and sensitivity of other hormones. Due mainly to soil depletion and inadequate diets, iodine deficiency is common in poor countries and is estimated to affect about one-third of the world’s population.
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Iodine and Thyroid Hormones
Iodine is especially important for the normal functioning of the thyroid gland. Iodine is the main element within thyroxine and triiodothyronine, thyroid hormones that regulate cellular metabolism and energy production. An overactive thyroid typically leads to weight loss, nervousness and higher body temperature, whereas an inactive thyroid leads to weight gain, severe fatigue and colder hands and feet, according to “Human Biochemistry and Disease.” In addition to thyroid hormones, iodine appears to be related to other hormones.
Iodine and Estrogen
According to Dr. David Brownstein, author of “Iodine: Why You Need It, Why You Can't Live Without It,” iodine can help maintain and correct the balance of estrogen, especially the estriol-form. After the thyroid gland, the ovaries have the second largest concentration of iodine in the body, which affects ovarian production of estrogens and changes in the estrogen receptors of breasts. As such, iodine deficiency results in increased estrogen production and increased sensitivity of estrogen receptors in the breast. Iodine therapy may be of benefit for helping control estrogen-dependent cancers, such as breast cancer. A study published in a 2005 edition of the “Journal of Nutrition” found that Japanese consumption of iodine-rich kelp may contribute to their lower incidence of hormone-dependent cancers.
According to the “Textbook of Medical Physiology,” essentially all hormone receptors are dependent on iodine to some extent, which increases the sensitivity of the receptor to the hormone it is related to. For example, iodine can increase the sensitivity of insulin receptors, which is of importance for diabetes, and it can increase the sensitivity of the receptors for neurotransmitters in the brain, such as serotonin and dopamine, which affect mood and cognition. Other hormones affected by iodine concentrations include testosterone, FSH, LH and cortisol.
Recommendations and Deficiency
The recommended daily intake for iodine is 150 mcg per day for both children and adults, according to “Advanced Nutrition: Macronutrients, Micronutrients, and Metabolism.” Taking too much iodine for many weeks or months can disrupt thyroid function and cause nausea. Iodine deficiency quickly leads to goiter, or inflammation of the thyroid, but not necessarily dysfunction. Long-term deficiency eventually results in hypothyroidism, or reduced output from the thyroid, but also changes in production and sensitivity for all hormones in the body. As such, iodine deficiency may be related to a wide-range of hormone-linked conditions, such as ovarian cysts, attention-deficit disorder, low IQ, senility, depression, breast and prostate cancers, diabetes and heart disease.