Minor Minerals Flashcards
List the minor minerals
Iron
Iodine
Zinc
Copper
Manganese
Selenium
Chromium
Molybdenum
Fluoride
What are the forms or iron in food?
Heme iron (ferrous iron) = Fe2+, found in haemoglobin and myoglobin of animal flesh
Non-haem iron (ferric iron) = Fe3+, iron found in plant foods, grains, supplements (can also come in the ferrous form), some minor amounts in meat
Iron cookware can also contribute to iron intake (important source for populations in development countries, or when dietary iron sources are scares)
In humans: Fe2+ for absorption, Fe3+ for transport (non-reactive form)
What are some factors that interfere with and enhance the bioavailability of iron?
Plant sources, even in iron enriched products = Phytic acid, oxalic acid, polyphenols, excess fibre
Increase absorption: High demand Low stores Heme iron in food Meat protein factor Vitamin C intake Gastric acidity (HCl from protein intake)
Meat, fish, HCl (caused by protein intake) and ascorbic acid enhance non-haem iron absorption when consumed together => conversion to Fe2+ for adequate absorption
Describe the absorption, transport, storage and excretion of iron
Absorption:
- As Fe2+ in SI, mediated by carrier proteins (DMT-1 and HCP-1) - Efficiency depends on body's iron status (average 18%; range 14-40%) - HCl in stomach and vitamin C enhance absorption by conversion of Fe3+ to Fe2+ form - Ferrireductase: enzyme in the brush-border also converts Fe3+ to Fe2+ - Excessive intake of calcium, zinc, phosphorus, manganese may chelate iron and interfere with its absorption (combined supplements may not be great)
Storage/carrier proteins in the enterocyte:
- Ferritin: binds and stores iron in enterocytes (and other tissues) - Irons does not enter bloodstream if body iron stores are high - Ferritin prevents excess absorption => "mucosal block" - Ferroportin: transports iron out of enterocytes when supplies are low for release into the blood - Hepcidin: regulates how much iron is released into the circulation. Takes ferroprotin into lysosomes for degradation (tightly regulated)
Transport:
- Ferrodisae enzymes: Ferroxidase (hephaestin) in enterocytes and ceruloplasmin in the blood (both copper-dependent metalloenzymes) convert Fe2+ to Fe3+ - Transported as Fe3+ bound to transferrin - In tissue cells: uptake by endocytosis; lysosomes release the iron, and transferrin is recycled
Storage:
- In the liver, bone marrow, spleen, bound to ferritin or hemosiderin
Excretion:
- Only 20% excreted, via bile and faeces; 90% recycled
Describe the functions of iron
- Oxygen delivery
- Haemoglobin = found in RBC, transports O2 and CO2, 4xFe-containing haem groups which bind 1 oxygen each (quaternary)
- Myoglobin = found in skeletal and cardiac muscle, stores O2, 1xFe-containing haem group binds 1 oxygen (tertiary)
- Oxidation-reduction reactions
- => can be harmful in high concentration, as iron forms free radical compounds
- Immune function
- Required for lymphocytes and natural killer cells production
- Iron-containing metalloenzymes
- Energy metabolism
- Involved in the first steps of the CAC and as cofactors of cytochromes in the ETC
- Alcohol and drug metabolism
- Hepatic cytochrome p450 detoxification systems enzymes and catalase require iron as cofactors
- Neurotransmitter synthesis
- Cofactor in enzymes involved in synthesis of dopamine, epinephrine, norepinephrine, serotonin
What are the requirements for iron?
RDI, UL
More required for women during childbearing age, more in pregnancy
Describe the signs and symptoms of iron deficiency and/or toxicity if relevant
Deficiency:
Iron-deficiency anaemia= microcytic hypochromic anaemia (decreased haemoglobin); decreased haematocrit (% blood volume containing RBCs), decreased serum ferritin, transferrin receptor number on cells increases
Symptoms = shortness of breath, fatigue with usual tasks, compromised immunity, depression, spoon-shaped nails
Most common minor mineral deficiency worldwide
At risk = premature infants, children child-bearing age women, vegetarians and vegans, regular blood donors, gastric ulceration
If during growth and development = impaired cognitive development that may be irreversible
Symptoms may be few initially when diet is changed (e.g. limiting iron sources) => iron stores are being used up
Toxicity:
Nausea, vomiting, stomach irritation, impaired absorption or other minerals
Hemochromatosis = genetic disorder when the mucosal block (ferritin storage) does not function adequately
Ferroportin is not regulated: despite high iron level, more is exported to the blood and take to tissues
Iron deposits and overload in liver, heart
If not managed, leads to liver cirrhosis, heart failure, elevated oxidative stress markers
Management includes: regulate blood “letting”, dietary advice to reduce high iron containing foods, chelation therapy
Describe the absorption, transport, storage and excretion of iodine
Digestion:
- Iodine is either bound to AA or found free is iodate (IO3-) or iodide (I-). During digestion, bound iodine is released and converted to iodide. Iodate is reduced to iodide (by ascorbic acid, protein thiol groups, glutathione*) - *Glutathione from food, acting in the gut, but overall this glutathione is poorly absorbed
Absorption:
- Iodide is absorbed in the stomach and duodenum - Goitrogens decrease iodine absorption and inhibit iodine use by thyroid gland: found in raw vegetables such as turnips, cabbage, brussels sprouts, broccoli, potatoes and cassava, as well as peanuts, soy, peaches, strawberries - Cooking reduces goitrogen activity
Transport:
- Bound to thyroglobulin, taken to the thyroid gland - Sodium dependent active transport system traps iodine in thyroid gland for hormone synthesis
Storage: Muscle, thyroid gland, skin, bone
Excretion: Via kidney/urine
Describe the primary functions of iodine
Thyroid hormone production:
- Synthesis of thyroxine (T4) and tri-iodothyronine (T3) - T4 is the form of thyroid hormone in the circulation, T3 is the active hormone form - T4 converted to T3 in cells by the iodothyronine-deiodinases (DIOs): selenium dependent metalloenzymes
Thyroid hormone functions:
§ Basal energy expenditure (BMR)
§ Overall energy metabolism
§ Growth and development in the foetus and infant
□ Brain and nervous system development. Full organ growth and maturation
