Iodine Flashcards
How much iodine does human body contains?
ultra-trace element (mineral NOT metal)
-contains 15-20 mg
70-80% found in thyroid
iodine (I-) form (anion)
Iodine RDA?
we cannot always say this food will have this many iodine because highly variable based on how much iodine from soil and food processing
human needs iodine (not vary hugely)
What are some sources of iodine?
food content variable based on soil and type of fertilizer used
- foods of ocean origin (vs. fresh water) contain higher levels of iodine
ex. seaweed, fish - Dairy products contain iodine via additives added to animal feed and use of iodine-containing disinfectants on cows, milking machines and storage containers (not always in there)
- iodized salt
How is iodine absorbed in the body?
Bound to amino acids in food
–>freed via digestion
in food as: free iodine (I-) or iodate (IO3-)
- absorb completely and rapidly from stomach (lesser in duodenum) >90%
- travels as free iodine in blood
- concentrates in thyroid gland by Na/I transporter (20x-50x conc. of plasma)
Where is iodine mainly absorbed?
stomach
>90% absorbed
What is the form that iodine travel in blood?
free iodine
What is the main function of iodine?
Synthesis of thyroid hormones:
- Thyroxine (T4) and Triiodothyronine (T3)
- T4 & T3 occupy on nuclear receptors–> gene expression
How is thyroid function regulated?
primarily regulated by thyroid-stimulating hormone (TSH)
TSH secreted by pituitary gland to control TH production and secretion
–>protecting body from hypothyroidism and hyperthyroidism
How is thyroid hormones transported in blood?
Protein bound:
thyroxine-binding globulin, albumin, transthyretin (prealbumin)
<0.1% not bound to a binding protein
What is the role of thyroid hormones in gene expression?
turn ON transcription of gene
-plasma protein w/ T4 and T3 travel to target cells these proteins
50x more T4 made than T3 –> bind to receptor on cell–> facilitated diffusion–> T4 converted to T3 (bioactive) in cells –>goes into nucleus and binds to nuclear protein receptor –> complex goes to regulatory region of gene
- ->promote transcription
- ->translation of new proteins
What is the role of thyroid hormones in gene expression?
- TH (T3, T4) circulate in blood bound to plasma proteins
- T4 and T3 enter cell where selenium-containing enzyme converts T4 –> T3
- T3 enters nucleus and binds to nuclear protein receptor
- T3-protein receptor complex binds to regulatory region of target gene
- Transcription of genes turned on–> increasing amount of mRNA made
- mRNA directs translation–> increasing synthesis of protein coded by target gene
- increase in the amount of protein–> cellular functions and body processes affected by this protein
What are some physiologic effects of thyroid hormones?
Adipose tissue: enhance lipolysis
Muscle: enhance contraction
Bone: promotes anabolism (growth and development)
CVS: increase heart rate
GI tract: stimulates nutrient digestion and absorption
Metabolism: stimulates metabolic rate and cellular oxygen consumption in metabolically active tissues (ex. muscle)
What are some interactions of iodine with other nutrients?
Impaired selenium status–> affects TH metabolism (via selenium-dependent iodothyronin-5’-deiodinases)
Iron, vit.A deficiencies may worsen effects of deficiency
- heme iron involved in TH synthesis (maybe attaching T3 to nuclear receptor)
- vit.A deficiency appears to reduce (not inhibiting) iodine uptake at thyroid gland and syn. of TH
Goitrogens interfere w/ iodine metabolism
-found in turnips, rutabaga, cabbage, cassava, and millet
-cooking reduces and not likely used enough to impact status in Ca.
-Cassava used as a dietary staple in some parts of the world
(Goitrogens: substance that affects iodine metabolism)
How is iodine being excreted?
Most in urine (kidneys dont have mech. to conserve)
- kidneys does not reabsorb
- feces (low)
-Sweat: potentially a problem in tropics (intake inadequate)
What are some factors affecting iodine RDA?
Geographical, ethnicity, cultural, religious reasons
iodine salts
biggest health concern: sodium
ex. hypertension patient can also be reducing iodine intake
-most salt in diet comes from processed package food (salt not iodized)
only salt for home use and store has to be iodized
What are some effects of iodine deficiency?
Reduces production of TH
-metabolic rate slows, weight gain (?)
Iodine deficiency and iodine deficiency disorders (IDD)
-Goiter (enlargement of thyroid in response to increased production of TSH)
-Cretinism: nuerological or hypothyroid
(deficient preg. women passed down to offspring)
-iodized salt, oil used for treatment
What is Goiter? (Iodine deficiency and iodine deficiency disorders (IDD))
enlargement or hyperplasia of the thyroid gland due to overstimulation by TSH
not permanent, reversible (several months-years)
What is Cretinism?
Iodine deficiency and iodine deficiency disorders (IDD)
iodine deficiency in fetus–> ID from mother
nuerological manifestations: cognitive, language, motor impairment
permanent, irreversible
iodine supp. may help mitigate
What is the toxicity of iodine?
UL = 1,100 microgram
based on thyroid dysfunction (elevated serum TSH)
How do we assess iodine status?
Urinary iodine excretion (recent dietary intake)
-due to variability–require duplicate measures
Thyroid size
Serum thyroid-stimulating hormone (TSH) conc.
WHO urinary iodine concentration recommended for nutritional sufficiency
<0.16 severe deficiency
> 2.37 excessive intake
What is the prevalence of iodine inadequacy?
mild iodine deficiency (3-79 yrs): just under 25%
-potential problem
UIC in non-preg. non-lac. women:
consume most dairy–>highest iodine level
No dairy–> marginally inadequate
–potential problem: babies may be endanger w/ hypothyroidism
is sea salt, which has not been iodized, a permitted ingredient of a food?
YES
sea salt which has not been iodized is permitted as an ingredient of a food
only salt for table or general household use to be iodized
-when salt/sea salt is sold for table/general household use–> must be iodized
more than 70 countries add iodine to salt
29-50% world’s pop. deficient
-mountain areas: most iodine -deficient
