Iodine

Question 1

What is a unique characterisic of iodine?

Answer 1

It is the heaviest element required for human nutrition (AW=127)

Question 2

What is iodine responsible for?

Answer 2

Responsible only for the synthesis of thyroid hormones

Question 3

What is the physiological significance of thyroid hormones?

Answer 3

Widespread therefore deficiency can be be fatal

Question 4

Prevalance of thyroid hormones deficiency

Answer 4

Still the largest public health problem in the world, particular for developing countries

Question 5

What is availability of iodine dependant on?

Answer 5

dependent on presence of Iodine in soil, which differs across the planet.

Question 6

How might iodine differ across soils?

Answer 6

Solubility of iodine in soil leads to variations in the bioavailability of dietary iodine since iodine is very soluble
* reduced when over-exposed to weathering (rain, snow and glaciation) and transport I back to the ocean.
* Iodine-poor regions include large mountainous ranges and heavily flooded area (Himalayas, Alps, Ganges river).
* Plants can contain up to 1.0 mg/kg dry weight of iodine but can be less than <0.01 mg/kg if grown in deficient areas.

Question 7

What are the best food sources of iodine?

Answer 7

foods arising from the sea

Question 8

What is the best reliable source of daily iodine?

Answer 8

iodized (fortified) table salt

Question 9

How has iodized salt impacted developed countries?

Answer 9

Rely more on processed foods so access to iodine fortified foods (salt, dairy foods, bread making etc).
* Has been the reason for almost eradicating deficiency in these countries.
* However, some recent changes to dietary habits maybe reducing Iodine intake (reducing salt intake).

Question 10

DRIs for iodine

Answer 10

Based on RDA
* AI for infants

Question 11

Food sources of iodine

Answer 11

• rich sources come from the sea
• variable sources which some might depend on soil
• fortified foods

Question 12

How is iodine absorbed?

Answer 12

Iodine rarely occurs as the element, but rather as a salt and is quickly and almost completely absorbed in the stomach and duodenum.

Question 13

Storage of iodine

Answer 13

15-20mg iodine is present in the body at any time, stored primarily in the thyroid gland (65%).
* Rest found in kidneys and other glands.
* Thyroid can concentrate Iodine 100-fold more than plasma levels.

Question 14

Excretion of iodine

Answer 14

Kidney is main site of excretion
* normal urinary levels 50ug/g of Iodine (expressed per creatinine) and approx. same concentration in plasma

Question 15

What kind of gland is the thyroid gland?

Answer 15

endocrine gland
* The thyroid hormones are released directly into the blood and travel to tissues and organs all over the body

Question 16

Where is iodine stored in the thyroid gland?

Answer 16

In the colloid of thyroid follicular cells as thyroglobulin (TG)
* Iodine goes into the cell and can be added to TG through enzyme reactions via thyroid peroxidase

Question 17

What protein is the thyroglobulin made up of?

Answer 17

tyrosine
* consists of two monomeric chains, each with 67 tyrosine residues.

Question 18

What is thyroglobulin

Answer 18

A protein made by the follicular cells and stored in the colloid of the thyroid gland which acts as a precursor to thyroid hormones.

Question 19

How can iodine be present on the TG?

Answer 19

• One Iodine molecule on the tyrosine = MIT (mono-iodotyrosine)
• Two Iodine molecules on the same tyrosine = DIT (di-iodotyrosine)

Question 20

What are the two hormones made by the thyroid?

Answer 20

• T3 → ACTIVE form → tri-iodothyronine
• T4 → INactive form → tetra-iodothyronine (thyroxine)

Question 21

How are T3 and T4 made?

Answer 21

A coupling reaction occurs that forms either T3 (DIT + MIT) or T4 (DIT + DIT) (bound to TG).

Question 22

How is T4 converted to T3?

Answer 22

T4 can be converted to T3 via microsomal enzymes that de-iodinate:
* Type 1 deiodinase - liver, kidney, thyroid
* Type 2 deiodinase - brain and adipose tissue, pituitary

Question 23

How are the thyroid hormones secreted from the colloid?

Answer 23

1. Thyroid stimulating hormone (TSH) is secreted from the pituitary and travels to thyriod through circulation
2. TSH binds to a G-coupled protein stimulating the second messenger system
3. The active protein kinase stimulates the apical side of the follicular cell to take up the TG-T3/T4 through endocytosis
4. the TG-T3/T4 is taken into cell and lysosome degrades the TG into the T3 and T4 components
5. T3 and T4 are released into circulation

Question 24

Role of T3

Answer 24

T3 enters cells and binds to nuclear receptors that activate the synthesis of genes and is responsible for regulating:
* Mitochondrial protein synthesis
* Lipid metabolism
* Carbohydrate metabolism
* Protein metabolism
* Ion transport
* Muscle contraction

Question 25

What happens with too much or too little T3?

Answer 25

* Too much: wired * Too little: sluggish

Question 26

What is the main role of T4 besides conversion to T3?

Answer 26

Secretion of T4 is involved in the negative feedback system which turns off the hypothalmus and anterior pituitary from releasing TRH and TSH respectively. * Without the negative feeedback too much TSH can be made

Question 27

What is the main disease of iodine deficiency?

Answer 27

Hypothyroidism of which primary cause is insufficient dietary intake of iodine to synthesis T4 so TSH secretion ↑ and the thyroid follicles enlarge resulting in a goiter * Minor cause can be consumption of excessive goitrogens (anti- thyroid substances/foods) such as cabbage, spinach, radish, soybeans, peanuts, peaches, strawberries (4% of cases)

Question 28

What are some recent dietary trends effecting iodine intake?

Answer 28

Plant-based foods * plant-based proteins * plant-based milk alternatives * vegetarian based diets

Question 29

How is iodine involved in radiation poisoning?

Answer 29

Uranium-235 decay can produce iodine-131which is volatile can be transmitted in the air and reside in the thyroid and cause cancer. Iodine supplementation can saturate the thyroid with non-radioactive iodide and reduce/minimize absorption of radioactive isoforms. * Generally iodine supplementation should take place 48 hours before or up to eight hours after radiation exposure.

Question 30

Other effective uses for iodine

Answer 30

* pink eye * foot sores * anti-bacterial surgical preparation * benign breast disease * breast pain * swelling and sores in mouth * lumps in the thyroid * Venous leg ulcers

Question 31

Iodine use for pink eye

Answer 31

eye drops containing iodine (povidone-iodine)

Question 32

Iodine use for foot sores

Answer 32

topical povidone-iodine

Question 33

Iodine use for surgical prep

Answer 33

povidone-iodine

Question 34

Use of iodine in benign breast disease

Answer 34

fibrocystic breast disease * molecular iodine, reduces fibrous breast tissue.

Question 35

Use of iodine in breast pain

Answer 35

mastalgia * 3000-6000 mg of molecular iodine for 5 months

Question 36

Iodine use for lumps in the thyroid

Answer 36

Taking iodine by mouth can improve lumps on the thyroid called thyroid nodules.

Question 37

Iodine use for venous leg ulcer

Answer 37

Leg sores caused by weak blood circulation * iodine reduces fibrosis