Specific tissues in the body utilize iodide and iodine. Adequate iodine status is essential for the production of normal levels of thyroid hormones and the integrity of thyroid and mammary glands, but iodine/iodide intake has decreased significantly over the past thirty years. Iodide, the reduced form of iodine, is highly concentrated in the thyroid gland where it is incorporated into thyroid hormones. Thyroid hormones regulate growth and metabolic rate, body heat and energy production, and neuronal and sexual development. Iodine is concentrated in the breasts where it is associated with protection against fibrocystic breast disease and cancer. Sub-clinical iodine/iodide deficiency has been associated with impaired mental function and loss of energy due to hypothyroidism.
The urinary iodine/iodide load test helps us determine if you are iodine deficient. You will be taking an oral dose of iodine/iodide (that will be sent to you), and you then collect your urine. The results of your test permits your doctor to obtain individualized results, and if you are iodine deficient your dosage can be precisely determined. The test is based on the concept that the body has specific and saturable mechanisms to take up iodine/iodide. When maximal retention is attained, the percentage of an iodine/iodide load that is retained decreases and the percentage urinary excretion increases.
The normal results should be that you excrete at least 80% of the iodine in a 24 hour period. Your report will graphically show you your results. See the sample report below.
Iodine status and metabolism is affected not only by iodine intake, which has decreased significantly, but also by intake and retention of goitrogenic halides (bromide and fluoride). Iodide uptake by specific cells is mediated by an energy-dependent
sodium/iodide symporter (NIS). Bromide and fluoride are non-essential, toxic halides that avidly compete with iodide for the NIS. Excessive intake of the antagonistic halides can accumulate in tissues, displace iodine and compromise the production of thyroid hormones and the integrity of the thyroid and mammary glands. Antagonistic bromide is abundant in commercially produced baked goods, soft drinks, pesticides, brominated chemicals and some medications. Primary sources of fluoride include fluoridated water, beverages, toothpaste, mouthwashes and some medications.
All animal life requires oxygen for sustenance, and
the human species is no exception. Oxygen drives the basic metabolic
processes that permit growth, development, reproduction, physical movement,
and constant body temperature. The complex of chemical interactions
necessary to sustain these processes is called metabolism, and the prime,
overall regulators of metabolism are the thyroid hormones.
The thyroid gland is located in the anterior part of
the neck in the midline. It consists of two lateral lobes lying on each side
of the thyroid cartilage (Adam's apple) and connected by a band of tissue
called the isthmus.
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It is one of the larger endocrine glands, and its
capacity to grow is phenomenal. Any enlargement of the thyroid, regardless
of cause, is called a goitre. The thyroid arises in the embryo from a
downward outpouching of the floor of the fetal pharynx, and a persisting
remnant of this migration is known as a thyroglossal duct.
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If viewed under a three-dimensional microscope, the resting thyroid is seen
as a collection of small, generally globular sacs, called follicles, filled
with the prohormone thyroglobulin. The cells lining these globules are
called follicular cells, and it is their function to synthesize thyroid
hormones as part of the prohormone thyroglobulin and either to secrete them
directly into the circulation or store them within the follicles. When the
individual's requirement for thyroid hormone increases, thyroglobulin is
split into its component parts, and the thyroid hormone thus released passes
through the follicular cells to enter the circulation. Nestled in the spaces
between the follicles are parafollicular cells. These, in essence, form a
separate endocrine organ. They have an entirely distinct embryological
origin, and they are not embedded in the substance of the thyroid gland, in
many species other than man (see the parathyroid glands: calcitonin.
The thyroid hormones are not proteins; rather, they
are modifications, called thyronines, of an amino acid, tyrosine. Thyroid
hormones are heavily laden with iodine. The major active thyroid hormones
are thyroxine (T4) and triiodothyronine (T3). Even though the thyroid gland
manufactures considerably more T4 than T3, T3 is roughly 2 1/2 times more
potent than T4. Indeed, in many ways, T4 serves as an additional,
circulating depot for T3 in that when T4 leaves the circulation and travels
through the cytoplasm to the nucleus of the target cell, its action at that
site is preceded or accompanied by its conversion to T3.
Most of the T4 and T3 secreted by the thyroid is bound to special proteins
(thyroxine-binding globulin [TBG] and prealbumins) in the serum, although
small amounts of these hormones travel freely in the serum and are readily
taken up by tissues to be replenished instantaneously from the T4 that had
been attached to the binding proteins.
Essentially all the cells in the body are target cells of thyroid hormones.
The major function of the thyroid hormones is to stimulate the synthesis of
protein once they have entered the cell nucleus. Another important function
is to stimulate the activity of the cell's mitochondria. These intracellular
organelles are the sites at which there is a controlled exchange of energy.
Some energy is conserved for the body's functionings, while the remainder is
dissipated as heat. The proportion of energy devoted to each of these
processes is controlled by the thyroid hormones. There are other
intracellular thyroid hormone functions that are not well understood, but it
is clear that thyroid hormones modulate protein, carbohydrate, fat, and
vitamin metabolism, as well as the generation of body heat. Thyroid hormones
also modify the activity of the autonomic nervous system.
| System or Event Affected |
Actions of T3/T4 |
| Basal Metabolism
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- increases basal metabolic rate
- increases body temp (calorigenesis)
- increases appetite
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Carbohydrate, lipid & protein
Metabolism
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- promotes glucose catabolism for energy
- stimulates protein synthesis
- increases lipolysis
- enhances cholesterol excretion in bile
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| Heart
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- promotes normal cardiac function
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| Nervous System
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- promotes normal neuronal development
in fetus and infant
- promotes normal neuronal function
in adult
- enhances effects of sympathetic
nervous system
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| Musculoskeletal
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- promotes normal body growth
and maturation of skeleton
- promotes normal function and development
of muscles
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| Reproductive
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- promotes normal female reproductive
ability and lactation
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