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Lecture 13

NUTR 3210 Lecture 13: micronutrients part 4

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Department
Nutrition
Course Code
NUTR 3210
Professor
David Mutch

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56
Micronutrients 4 essential trace minerals
Iron
Iron is found in a lot of different foods at low levels
- Rich in liver, meats, and plant sources (e.g., leafy green vegetables, fruits, nuts)
In foods, iron can be found in one of two forms:
1. heme (within the porphyrin ring of hemoglobin and myoglobin) animals
2. non-heme plants
Only two states of iron are stable in the aqueous environment of the body and in food: Fe3+ (ferric) and
Fe2+- (ferrous)
Functions of iron in the body include:
1. oxygen transport (i.e., important for hemoglobin and myoglobin)
2. redox reactions is an active component of the electron transport chain (iron sulfur centers and cytochrome
heme proteins)
- Not necessarily not bad, but can promote radicals (context dependent)
3. iron metalloenzyme enzymes dont function if they dont have iron
RDA -> 8mg/d men, 18 mg/d women, 27 mg/d pregnancy
- Higher for women due to menses /since women lose iron
- Higher in pregnant women to cover the needs of the fetus
UL -> 45mg/d (this leads to hemosiderosis)
Different forms, different absorption
Between 10-18% of the iron ingested is absorbed
- How much is absorbed will depend on a
persons iron status
- /dont want an overload so its regulated
Non-heme iron
- HCl and proteases cleave non-heme iron from
food components in stomach releasing mostly
ferric (Fe3+) iron
- Stomach acid converts most Fe3+ into ferrous
iron (Fe2+)
- Any remaining Fe3+ is reduced by a reductase
in the small intestine into Fe2+
- Fe2+ is transported by divalent metal
transporter 1 (DMT1)
- /all ferric ions need to be changed to ferrous
ions in order to enter the cell
Heme iron
- Released from hemoglobin/myoglobin by
proteases in the stomach and small intestine
- Heme (porphyrin ring) is taken up in the small
intestine by heme carrier protein 1 (HCP1)
- Inside small intestinal cells, the heme
porphyrin ring is broken down by heme
oxygenase into Fe2+ and protoporphyrin
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57
Factors Influencing Iron Absorption
Chelators are small organic compounds that form a complex with a metal ion
- This can affect iron absorption /can regulate or affect absorption
- If the iron-chelate is soluble, then absorption is enhanced
- If the iron-chelate is insoluble, then absorption is inhibited /if someone has high absorption best to use
insoluble chelator
Examples of enhancers: vit C, and some evidence for specific soluble fibres (pectin)
- Vit C acts as a reducing agent for ferric ion
- /favourable state for absorption to change Fe3+ to Fe2+
Examples of inhibitors: polyphenols (in tea and coffee), oxalic acid (in spinach), and insoluble fibres
- Coffee just after a meal reduces iron absorption by ~50%
- Oxalic acid binds with iron (and other metals too), preventing its absorption
o /insoluble fibres increase time in the gut and increase competition,
Iron distribution and metabolism
Iron is transported in the blood in the ferric form bound to transferrin which is a carrier protein
Important that iron be bound by a carrier because unbound ferrous (Fe2+) iron has a high redox activity which can
readily lose an electron to produce free radicals (interacts with H2O2)
/In order to pass thru the small intestine iron ions need to be changed to ferrous ions
/in order to be transported in the blood it must be changed by ceruloplasmin to ferric ions to be bound to
transferrin
/when transferrin is unbound it will be recycled
/when there is too much iron can be accessibly stored as ferritin but when there is too much it will be stored as
hemosiderin which is less excessible
/too much hemosiderin will lead to too much accumulation in the body so we want to get out hemosiderin from
the body
/reduce Fe3+ to Fe2+ and then again to Fe3+ for it to be bound to transferrin, this is all done to prevent free ferrous
ions
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Description
Micronutrients 4 essential trace minerals Iron Ironisfound in a lot of different foodsat lowlevels - Rich in liver,meats,and plant sources(e.g.,leafy greenvegetables,fruits,nuts) Infoods,iron can be found in one of twoforms: 1.heme (within the porphyrin ring of hemoglobinand myoglobin) animals 2.non-heme plants Only twostates of iron are stable in the aqueousenvironment ofthe bodyand infood:Fe (ferric)and 2+- Fe (ferrous) Functions of iron in the body include: 1.oxygen transport (i.e.,important for hemoglobinand myoglobin) 2.redox reactions isan active component oftheelectrontransport chain(ironsulfur centersandcytochrome heme proteins) - Not necessarily not bad,but can promote radicals(contextdependent) 3.iron metalloenzyme (enzymes dont functioniftheydont haveiron) RDA ->8mg/d men,18 mg/d women,27 mg/d pregnancy - Higher for women due tomenses /since womenloseiron - Higher in pregnant women tocover theneedsofthe fetus UL->45mg/d (thisleads to hemosiderosis) Different forms, different absorption Between 10-18%of the iron ingested isabsorbed - How much isabsorbedwilldepend on a personsiron status - /dont want an overloadsoits regulated Non-heme iron - HCl and proteases cleave non-heme ironfrom food componentsin stomach releasing mostly 3+ ferric (Fe ) iron - Stomach acid convertsmost Fe intoferrous iron (Fe ) 3+ - Any remaining Fe isreducedby a reductase in the smallintestine intoFe 2+ - Fe istransported by divalent metal transporter 1 (DMT1) - /allferric ions need tobechanged toferrous ions in order toenter thecell Heme iron - Released from hemoglobin/myoglobin by proteases in the stomach and smallintestine - Heme (porphyrinring) istaken up inthe small intestine by heme carrier protein 1 (HCP1) - Inside smallintestinal cells,the heme porphyrin ring isbrokendown by heme oxygenase into Fe and protoporphyrin 56Factors Influencing Iron Absorption Chelatorsare smallorganic compoundsthatformacomplex withametalion - Thiscan affect iron absorption /can regulateoraffect absorption - If the iron-chelate issoluble,then absorptionisenhanced - If the iron-chelate isinsoluble,then absorptionisinhibited /ifsomeone hashighabsorptionbesttouse insoluble chelator Examplesof enhancers:vit C, and some evidencefor specificsolublefibres(pectin) - Vit C acts asa reducing agent for ferric ion - /favourable state for absorption tochangeFe toFe 2+ Examplesof inhibitors:polyphenols(in tea and coffee),oxalicacid(in spinach),and insolublefibres - Coffee just after a meal reduces iron absorptionby~50% - Oxalic acid bindswith iron (and othermetalstoo),preventingitsabsorption o /insoluble fibres increasetime inthegut and increase competition, Iron distribution and metabolism Iron is transported in the blood in the ferric form bound
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