17.3: Iodine
- Page ID
- 58199
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)In anticipation of the fall-out of radioactive iodine from the 1986 Chernobyl nuclear accident, many people in countries downwind from the accident took iodine pills. They did this to protect the thyroid gland.
Thyroid cancer rates rose after the accident among children living in cities near Chernobyl.
The rationale behind their action was that iodine is an essential part of thyroid hormone, the hormone necessary for normal metabolism, and iodine is concentrated in the thyroid gland for the purpose of making this hormone. The iodine pills saturate the thyroid gland with iodine so that very little of the radioactive iodine would be taken up by the gland.
Simple Goiter—The Iodine Deficiency Disease
Iodine is required in the diet for the purpose of making thyroid hormone. Not enough iodine means not enough thyroid hormone, and this results in a condition called simple goiter, characterized by an enlargement of the thyroid gland. The thyroid gland enlarges in its attempt to make more hormone. Because the thyroid gland is located in the neck, the enlarged gland protrudes and enlarges the neck.
Until 1924, when iodized salt (iodine added to salt) was introduced, simple goiter—and an enlarged neck—was common in this country. During World War I, the neck sizes of the men drafted from all parts of the U.S. reflected the geographical distribution of goiter.
The effect of simple goiter depends on the extent of the iodine deficiency and also on when the deficiency occurs. A severe iodine deficiency during fetal life can interfere with normal physical and mental development, whereas a slightly enlarged thyroid gland may be the only noticeable effect of a mild iodine deficiency during adulthood. Intermediate symptoms of inadequate thyroid hormone include sluggish mental activity and weight gain, and “puffiness” due to abnormal retention of water in tissues.
Goiter, by definition, is simply an enlargement of the thyroid gland, located in the neck. The enlarged thyroid causes a protrusion in the neck.
Iodine deficiency is still a worldwide problem, especially in developing countries. Particularly poignant is the story of Jixian village in rural China.5 In 1978, iodine deficiency was so severe and so prevalent that most of the village suffered from symptoms of severe iodine deficiency, such as intellectual disability. Ironically, Jixian village means village of scholars. An intensive campaign to eradicate iodine deficiency was implemented, and by 1985, severe iodine deficiency was absent in children younger than age 7. The physically and mentally normal children helping their impaired parents became a common sight in the village.
Iodine in Food
The most consistent sources of dietary iodine are foods from the sea. As long ago as 3000 B.C., the Chinese used burnt sea sponge to treat simple goiter, even though they didn’t know what caused the disease. The treatment was effective because sea sponges contain iodine, and, as a mineral, iodine isn’t destroyed when the sponge is burned.
Inland, the iodine in food varies. Plants don’t need iodine to grow, so its presence in plants depends on the amount in the soil, water, and environment. Goiter was least common among those who lived next to the sea, not only because seafood is available there, but because the soil next to the sea is rich in iodine.
In the American diet, the main sources of iodine are iodized salt, seafood, and processed foods to which iodine compounds have been added.
Excess Iodine
Moderate excesses of iodine isn’t a problem for most people. However, even safe levels for healthy people can be a problem for those with autoimmune thyroid disease (common in older women in the U.S.) and some other conditions.
Ironically, large excesses of iodine can inhibit the production of thyroid hormone and cause goiter (another example of “too much or too little” as a problem). In Japan, for example, some people get goiter from regularly eating large amounts of iodine-rich seaweed. Moderate excesses of iodine are efficiently excreted in the urine.
Figure 17-5: Iodine deficiency is the primary cause of preventable brain damage and intellectual disability worldwide.