Iron

Question 1

What are the chemical forms of iron?

Answer 1

Exists in several oxidation states

Only stable in the body’s aqueous environment and in foods as: Fe2+ ferrous iron and Fe3+ ferric iron

Iron also found in the body in the heme form

Question 2

What are the metabolic roles of iron?

Answer 2

Binding and transport of oxygen
Energy metabolism
Co-factors for various proteins
Antioxidant protection
Antimicrobial function

Question 3

What are the food sources of iron?

Answer 3

Heme iron (Fe2+ ferrous form): liver, red meat, seafood

Meats provide heme but they also contain non-heme iron

Non-heme iron (Fe3+ ferric form): Spinach, collards, broccoli and about 50% of the iron in animal foods

Question 4

Is iron-fortified in Canada?

Answer 4

It is mandatory for flour fortification of wheat flour in Canada
4.4 milligrams of iron

Question 5

How is heme iron digestion and absorption?

Answer 5

Hemoglobin/myoglobin - hydrolysis of heme from globin portion catalyzed by protease in stomach/small intestine

Heme remains soluble
- absorption intact in the duodenum and proximal jejunum
- carrier-mediated transport (hcp1) across brush border membrane
- in the enterocyte, the release of iron from heme in Fe2+ form
- 25% of heme iron from foods is absorbed

Question 6

How is non-heme iron digestion and absorption?

Answer 6

Non-heme iron bound to components of foods - hydrolysis of iron, mostly in form of Fe3+ catalyzed by hydrochloric acid (HCl) in stomach catalyzed by protease in stomach/small intestine

Fe3+ reduced to Fe2+ prior to absorption
- reduction partially achieved in stomach; mostly through various reductases in brush border membrane
- carrier-mediated transport with divalent mineral transporter 1 (DMT1) across the brush border membrane = regulatory step of iron absorption -> synthesis of DMT1 affected by iron status

Question 7

What are some enhancers the influence the absorption of iron?

Answer 7

Acids, eg. ascorbic, citric, lactic acid
Acidic pH
Meat, fish, poultry (MFP) factors
Chelators, eg., sugars (fructose and sorbitol)

Mechanism
- reduce iron to ferrous form
- maintain soluble complexes with iron to enhance absorption

Question 8

What are the inhibitors that influence the absorption of iron?

Answer 8

Polyphenols such as derivatives found in tea and coffee (can reduce absorption by up to 50%)

Oxalic acid found in spinach, chard, berries, chocolate, tea and others

Phytic acid sound in whole grains, legumes, lentils, nuts, and seeds

Some minerals, such as calcium, zinc, and manganese

Question 9

Dietary Reference Intakes

Answer 9

EAR, RDA
Have them for infants and toddlers
Pregnancy and lactation

Question 10

How do vegetarians meet their requirements?

Answer 10

Requirement for iron is 1.8 times higher for vegetarians

Question 11

What are the 3 possible fates of iron upon absorption into enterocytes?

Answer 11

1. used by intestinal cells in a functional capacity (e.g., cofactor)
2. stored in the storage protein ferritin (as Fe3+
3. transported across the basolateral membrane to enter circulation for transport to body tissues
   - carrier-mediated (via ferroportin)
   - coupled with the oxidation of ferrous iron (Fe2+) to ferric iron (Fe3+) copper-dependent reaction (hephaestin)
   - Fe3+ binds to transferring = transport protein in plasma -> distribution of serum transferrin Fe3+ via liver to tissues