Iodine supplementation

Question 1

How much iodine is recommended daily?

Answer 1

150 ug/day

Question 2

What are good dietary sources of iodine?

Answer 2

• cows milk (non-organic) ~50-80 ug/portion
• yoghurt ~50-100 ug/portion
• white fish ~115 ug/portion

Question 3

Key facts about iodine: molecular weight, melting point, state on Earth, biogeochemistry

Answer 3

• Mw: 126
• Melts at 114 degrees C
• usually in oxidised (iodine) form on Earth due to being oxidised by ozone or UV
• Greatest levels found in seaside soils, clay-like

Question 4

Synthesis of thyroid hormones (included negative feedback loop, biochemistry)

Answer 4

• Thyroid hormone T4 is synthesised from the thyroid gland
• negative feedback loop: when low concentrations, hypothalamus releases thyrotropin releasing hormone to anterior pituitary gland which released thyroid stimulating hormone which activates the thyroid. In high levels the hypothalamus is inhibited
• Thyroglobin is synthesised on the ER in the thyroid gland and is exocytosed with L-tyrosine amino acids ‘sticking out’
• once exocytosed, iodine is added to tyrosine chains via iodination
• there is then conjugation between adjacent iodated tyrosines
• These are then endocytosed and proteolysis forms T4
• T4 leaves the cell via MCT channel and into periphery
• deiodinase in periphery then breaks down to T3 which acts as a transcription factor for protein synthesis genes and upregulation of energy metabolism

Question 5

Selenium deficiency: Keshan disease, Kashin-Beck disease, Se deficiency in TPN

Answer 5

• Keshan disease: observed in China. Deficiency increases susceptibility to Coxsackie B virus. Symptoms are an enlarged heart, arrhythmia, cardiac myopathy
• Kashin-Beck disease: associated with Se deficiency. Occurs in 0-20 year olds. Characterised by stiffness of joints, limb weakness: osteoarthritis
• Se deficiency in TPN: occurs when Se not added to bags properly. Causes cardiomyopathies, muscle pain, tenderness and reduced mobility

Question 6

How selenium deficiency is related to iodine deficiency (GLUTPx, deiodinase, thioredoxin reductase)

Answer 6

• Selenocysteine (‘21st amino acid’) coded by UGA and 3’stem loop structure which recruits SBP2 to bind and EFsec to be added to protein
• GLUTPx: uses selenocysteine in structure which is involved in T4 synthesis
• Deiodinase: Used for T3 synthesis
• thioredoxin reductase: antioxidant function which regulates NFkB and dampens inflammation
• all 3 enzymes are expressed in the thyroid in large quantities

Question 7

The different grades of goitre

Answer 7

• 0: nothing
• 1: palpable when neck raised
• 2: visible when neck in neutral position, and palpable

Question 8

Spectrum of iodine deficiency disorders: from foetus to adult

Answer 8

• foetus: risk of stillbirth, cretinism, squint, mute-deaf
• Neonate: hypothyroidism, goitre
• child: hypothyroidism, goitre, impaired mental function
• adult: hypothyroidism, goitre (which can cause breathing problems when asleep), impaired mental function

Question 9

Potential measures for iodine supplementation

Answer 9

• iodised oil
• iodised salt (needs to be kept in closed packets)
• iodised water
• fortifying crops

Question 10

Measuring iodine deficiency

Answer 10

• urine analysis
• old-fashioned method: Sandell-kathoff reaction between iodine and Cerium. Turns from yellow to colourless-> can be measured via spectroscopy

Question 11

What is the current status of iodine deficiency in the UK

Answer 11

• Schoolgirls study found 51% had a mild deficiency, 16% had moderate and 1% had severe