Iodine is an essential trace element for human health, which is vital to the function of the thyroid gland.
Thyroid hormones are iodinated thyronines, formed from enzymatic coupling of iodinated tyrosine residues within protein thyroglobulin.
Iodine is necessary for thyroid hormones: thyronine (T4) and triiodothyronine (T3), which are involved in growth and development.
Iodine is present in low amounts in soil, but is plentiful in oceans and in sea plants (seaweed).
Majority of iodine in the body is present in the thyroid gland.
The human thyroid gland must trap approximately 60 mcg of iodide daily against a steep gradient of the element to ensure an adequate supply of hormones.
Dietary iodine is primarily in the form of iodide or is converted to iodide in the GI tract by reduction. Iodide is completely and rapidly absorbed throughout all areas of the GI tract.
The terms iodine and iodide are frequently used interchangeably.
A moderate iodine deficiency may result in goiter (enlarged thyroid gland).
According to NHANES III (1988-1994) data, dietary
iodine intake has decreased dramatically in the past 20 years.1 In
addition, there was a 10-fold rise in iodine deficiency from NHANES I data,
with the highest incidence of deficiency occurring among female Caucasians
between the ages of 40-49.
Iodine’s major function in the body is its role in the formation of thyroid hormones. Thyroid hormones stimulate basal rate of
metabolism, oxygen consumption and heat production. They are necessary for
normal nervous system development and linear growth. Most organ systems are
directly or indirectly under the influence of thyroid hormones.
A deficiency in iodine leads to a fall in the production of thyroid hormones, and an increase in thyroid-stimulating hormone (TSH) from the pituitary gland. This can lead to an enlargement of the thyroid gland, or goiter.
In addition to goiter, an iodine deficiency may also have negative effects on growth and development, especially in the brain.
Substances called goitrogens occur naturally in foods and can also cause goiter by blocking absorption or utilization of iodine. Some foods that contain goitrogens are:
However, cooking inactivates these substances.
A severe iodine deficiency, particularly during gestation or early postnatal growth, results in cretinism. Cretinism is a syndrome characterized by both mental and physical retardation. Mental deficiency, quadriplegia, deaf mutism, a shuffling gait, shortened stature, and hypothyroidism (reduced thyroid activity) are caused by cretinism. In addition, a severe iodine deficiency may result in endemic myxedema in adults, which causes hypofunction of the thyroid gland and a slower metabolic rate, anemia, enlarged tongue, slow speech, puffiness of hands and face, problems with the skin and hair, drowsiness, and mental apathy.
A selenium deficiency exacerbates an iodine
deficiency because of the resulting decrease in enzyme activity that is
required for thyroid hormone synthesis.
There may be a trend of iodine deficiency in certain subsets of the population. Iodine deficiency in women of reproductive age is of particular concern, because mothers with severe iodine deficiency can develop goiter, which can potentially lead to children born with a reduced intellectual capacity.
Iodine is especially vital to the growth, mental development, and survival of infants. The main source of iodine for breastfeeding infants is from human milk.
Vegetarians who exclude animal products may be at
increased risk of iodine deficiency.
Caution with pregnancy or nursing, consult physician
Information on the relationship between substances and disease is provided for general information, in order to convey a balanced review of the scientific literature. In many cases the relationship between a substance and a disease is tentative and additional research is needed to confirm such a relationship.
Breast Cancer: Although further studies are needed, the role of iodine in benign breast disease may have beneficial effects. A paper reviewed 3 clinical studies to determine subjective and objective responses from patients with fibrocystic breast disease during iodine replacement.7 Overall, iodine supplementation reduced breast fibrosis, while at least a 65% objective improvement was noted with all types (protein-bound, sodium, molecular) of iodine treatment. Some side effects were significant, however pain relief was found among subjects receiving iodine replacement.
Mental Development: Recently it has been shown that micronutrient deficiencies (i.e. iodine, iron) can affect mental development and learning capacity of children.8 One study showed that fortification of a biscuit with iron, 60 mcg of iodine, and b-carotene resulted in a significant improvement in the micronutrient status of primary school children from a poor rural community.8 In addition, fortification significantly improved cognitive function with the digit span forward task (short-term memory). Micronutrient status of children should be frequently assessed, since prevalence of certain nutrient deficiencies (iodine, iron, vitamin A) has increased in children and pregnant women. 9
Vegetarian Diet: An
experimental diet study on 6 healthy adult volunteers was done on four separate
5-day diet periods. An assessment was done on isoenergetic normal, protein-rich,
and lactovegetarian diets containing no iodine food sources or foods fortified
with iodine. After diet assessment, an analysis was performed and found reduced
iodine intake and urinary iodine excretion in the lactovegetarian diet compared
to the other two diets. Results indicated that iodine supply is higher in
non-vegetarian diets than with vegetarian diets. In addition, those following
stricter forms of vegetarian practices (e.g. vegan, lactovegetarian) may be
limiting their dietary iodine intake.10
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