Iodine Metabolism

Gandham. Rajeev

The total body contains about 20 mg of iodine.

80% is present in the thyroid gland.

Muscles, salivary glands & ovaries also

contain some amount of iodine.

Sources:

Rich sources of iodine are sea foods, eggs,

dairy products, vegetables & iodized salts.

RDA:

150 - 200 µg/day

Metabolism

Iodine is absorbed from upper small intestine.

Iodine is transported in plasma by loosely

binding to plasma proteins.

Iodine absorption also occurs through skin &

lungs.

80% of body’s iodine is stored in the organic

form as iodothyroglobulin in thyroid gland.

Iodothyroglobulin contains thyroxine,

diiodotyrosine, & triiodothyronine.

About 2/3rd of iodine is excreted through urine.

Also excreted through bile, skin & saliva.

Plasma iodine: 4 – 10 mg/dl.

Most of this is present as protein bound iodine

(PBI).

It represents the iodine levels.

Functions

The most important function of iodine in the

body is in the synthesis of thyroid hormones,

triiodothyronine (T3) and tetraiodothyronine

(T4), which influence large number of

metabolic functions.

Disease states

Causes of iodine deficiency

Dietary deficiency & ingestion of goitrogens in

the diet.

A deficiency of iodine in children leads to

cretinism and in adults goitre.

The most common cause is dietary deficiency

Goiter

Abnormal increase in the size of the thyroid

gland is known as goiter.

Decreased synthesis of thyroid hormones & is

associated with elevated TSH.

Goiter is primarily due to a failure in the auto

regulation of T3 & T4 synthesis.

This may be caused by deficiency or excess of

iodide

Goitrogenic substances (goitrogens)

These are the substances that interfere with

the production of thyroid hormones.

Include thiocyanates, nitrates & perchlorates.

Drugs such as thiourea, thiouracil,

thiocarbamide etc.

Plant foods - cabbage, cauliflower contain

goitrogenic factors (mostly thiocyanates)

Simple endemic goiter

Due to iodine deficiency in the diet.

Mostly found in the geographical regions,

where the water & soil are low in iodine.

Consumption of iodized salt is advocated to

overcome the problem of endemic goiter.

In certain cases, administration of thyroid

hormone is also employed.

Hypothyroidism in children is associated with

physical & mental retardation, known as

critinism.

Critinism

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