21 - Iron

Question 1

What is a summary of the role of iron?

Answer 1

Iron is a co-factor for many proteins and is involved in many important cellular functions

Question 2

Iron overload?

Answer 2

Haemochromatosis. Common - 1/3 in NZ

Question 3

What are the MAJOR minerals?

Answer 3

Minerals present in over 5 grams (teaspoon)
Include calcium, phosphorus, magnesium, potassium, sulphur, sodium, chloride
We have a high requirement of calcium as it is needed for bone mineralisation which has a high turnover

Question 4

What are the trace minerals and how much of them do we need?

Answer 4

Minerals present in less than 5g
Iron, zinc, copper, iodine, selenium (NZ has low amounts of iodine and selenium in our soils but don’t commonly see primary deficiencies
Smaller amounts of trace minerals are needed as homostatic regulation is tighter

Question 5

Is iron a major or trace mineral?

Answer 5

trace

Question 6

What is the most common deficiency in the world?

Answer 6

IRON deficiency

Question 7

What are 6 functions of iron in the body?

Answer 7

In…

1. haemoglobin - blood protein has heme iron that enables O2 transport
2. myoglobin - O2 delivery to tissues
3. cytochromes - assists in electron transfer and storage of energy through redox reactions of iron (Fe2+>Fe3+)
4. ribonucleotide reductase - DNA production
5. succinate dehydrogenase - FA oxidation
6. collagen synthesis

Question 8

Since iron is so important why do we only need a trace amount in our diets?

Answer 8

It is very well and tightly regulated at the RBC level
RBCs have 2.5g of iron and only live for 120 days - they are broken down and remade and we recycle that iron it isn’t lost.

Question 9

How big are the body stores of iron

Answer 9

1g

Question 10

What is the daily intake of iron?

Answer 10

1-2mg and daily intake and daily loss of iron equal each other as we are constantly recycling the iron in our body

Question 11

What is the bioavailability of iron like?

Answer 11

LOW but variable depending on physiological factors i.e. during pregnancy and growth RBC production increases, and dietary factors

Question 12

What are the steps in iron recycling?

Answer 12

1. Bone marrow incorporates iron into the HB of RBCs and stores excess as ferritin
2. Carries O2 in blood
3. Lost in bleeding
4. Liver/spleen breakdown RBCs and recycle iron packaging it into transferrin and excess as ferritin
   > excess stores can damage liver (haemochromatosis)
5. LITTLE lost as sweat and urine
6. Transferrin transports iron in blood to BM to be packaged into RBCs or to muscle as myoglobin

Question 13

How is iron always found in the body and why is this beneficial?

Answer 13

bound to a protein - transferrin and ferritin acts as biomarkers for assessing iron status

Question 14

Where does most of the absorption of iron occur?

Answer 14

DUODENUM

Question 15

How is iron stored when we eat it?

Answer 15

At the duodenum excess iron is stored in mucosal cells/enterocytes as ferritin. Only if we need this iron somewhere in the body is it released to mucosal ferritin then to another transferrin which allows it to be transported through the blood.
If iron is NOT needed/is in excess then the enterocytes are just shed and the iron is lost (occurs every 2-3 days)

Question 16

Who may have iron absorption problems?

Answer 16

• surgery i.e. bilroth 1 or 2 for cancer and peptic ulcers
• issues with enterocyte integrity (celiacs)
• malabsorption
• SI removed

Question 17

Heme iron?

Answer 17

• ANIMAL sources
• absorb 25-30% from our diet
• heme iron is easily absorbed from the gut lumen into the enterocyte
• requires heme oxygenase to remove HB from iron
• stored in cell as ferritin
• not much can interfere with the absorption of heme iron

Question 18

Non-heme iron

Answer 18

• plants/veg/cereals/supplement/cereals
• iron salt (fe2+)
• more difficult to absorb as has to be reduced to Fe2+ from Fe3+ so has to be solubilized by enzymes on the membrane of the enterocyte and things in our diet
• is absorbed by a metal transport protein
• stored as ferritin along with heme after being converted BACK to Fe3+

Question 19

What is bioavailability of iron dependent on?

Answer 19

It is different depending on amount of non heme and heme we eat

Question 20

What is on the BL membrane on the enterocyte?

Answer 20

Regulatory proteins that allow iron to be taken up into the blood as transferrin
Hormone hepcydine secreted by the liver regulates iron movement into the blood

Question 21

what hormone from the liver regulates iron movement out of the cell and into the blood?

Answer 21

Hepcydine

Question 22

Describe how iron is tightly regulated

Answer 22

Always bound to a protein and stored if not needed - don’t have free iron floating around in body and is continuously recycled

Question 23

What happens to iron once it is released from intestinal cells?

Answer 23

Once it is in the blood as transferrin it is taken up by cells with a transferrin receptor. Binds and iron is released in to cells. When macrophages break down RBCs the iron is passed onto transferring and into the blood

Question 24

2 ways iron gets into blood?

Answer 24

Release from enterocytes via dietary intake

Breakdown of RBCs by macrophages

Question 25

Compare heme and non-heme iron

Answer 25

Heme - ONLY animal sources - don't consume much (10%) but is more readily absorbed (25%) Non-heme - plant and animal sources - ingest a lot (90%) BUT is not well absorbed (17%) as it has to be solubilized at the duodenum etc - vege/vegans need to consume lots as it isn't absorbed well

Question 26

Why is non-heme iron not absorbed as easily

Answer 26

- more steps required - reduced to Fe2+ and solubilised by membrane enzymes - absorbed by metal transport protein - converted back to Fe3+ to be stored as ferritin - regulatory proteins for release

Question 27

What 5 things ENHANCE non-heme absorption/make it more bioavailable at the enterocyte level?

Answer 27

- MFP (meat factor protein) - vitamin C (strongest enhancer) - HCl from stomach - helps solubilise and make more bioavailable - lactic acid - sugar

Question 28

What 6 things INHIBIT non-heme absorption/less bioavailable?

Answer 28

- fibre - oxalates (BIND non-heme iron - spinach, strawberries, rhubarb - calcium - phosphorus - tannin - polyphenols

Question 29

What 3 foods have the highest amounts of iron?

Answer 29

- spinach (but non-heme so not absorbed well at all) - red meat/steak - chicken

Question 30

Besides food what are other sources of iron?

Answer 30

- supplements with vit C | - contamination iron; contamination of cooking vessels into food. Intervention used in populations at risk of deficiency

Question 31

What needs to be provided with iron supplements to aid bioavailability

Answer 31

Vitamin c as it is non-heme

Question 32

What are the RDIs of iron?

Answer 32

very variable | The recommended intake of iron depends on the physiological ages and stages of growth

Question 33

What populations are at risk of iron deficiency/have increased requirements

Answer 33

- infants (not breastfeeding as breastmilk as iron that is absorbed well) - adolescence - menstruating females (blood loss) - NOT as high in men - pregnancy; have increased blood volume AND requirements for fetus

Question 34

Vulnerable groups

Answer 34

infants toddlers adolsents esp menstruating females pregnant women

Question 35

What are the 3 stages of iron deficiency?

Answer 35

1. Depleted iron STORES 2. Iron restricted erythropoiesis 3. Iron deficiency anaemia

Question 36

Depleted iron stores?

Answer 36

- 1st stage in iron deficiency - lower serum ferritin - 1/10 women have this but don't have a lot of symptoms, may be tired, hard to detect without a blood test of the biomarkers - biomarker: drop in serum ferritin

Question 37

Iron restricted erythropoiesis?

Answer 37

- stage 2 of iron deficiency - restriction of making new RBCs - once iron storage has become depleted there isn't enough iron to make RBCs so serum TRANSFERRIN that transports iron around the blood starts to drop - biomarker: drop in serum transferrin (saturation)

Question 38

Iron deficiency anaemia?

Answer 38

- 3rd stage in iron deficiency - don't make enough or adequate sized RBCs as iron too low so aren't carrying enough HB or oxygen - feel VERY tired and easily exhausted as not enough O2 - biomarker: drop in HB

Question 39

What does iron deficiency look like

Answer 39

microcytic anaemia - pale and small RBCs | Produces the SAME symptoms as folate/B12 deficiency

Question 40

What else can you measure to help diagnose iron deficiency ?

Answer 40

MCV will decrease

Question 41

What percentage of children 0-4 have iron deficiency world wide?

Answer 41

43% - very common | higher in developing countries

Question 42

What do they do in countries where iron deficiency is very prevalent?

Answer 42

interventions like the micro-nutrient sprinkle | education campaigns

Question 43

Do we have mandatory fortification of iron?

Answer 43

no it is mandatory. We only pick up iron deficiency by screening

Question 44

In what ethnicity groups of adolescents is iron deficiency more common?

Answer 44

Maori and pacific compared to NZ European (15%)

Question 45

iron is vital for .... and ...

Answer 45

growth and development young children and adolescents grow rapidly so need iron max amount of growth occurs in utero and in first few months of life - nutrition has a large impact in early stages of life especially important for brain development

Question 46

What are 4 problems that can occur for in infants due to iron deficiency? And what does this mean for clinical practice?

Answer 46

1. irreversible effects in cognition and brain development 2. myelination 3. neuron growth and differentiation 4. neurotransmitter regulation Means we need to screen and detect iron deficiency in early life before this irreversible problems occur

Question 47

Pregnant women and iron?

Answer 47

- VERY high requirements hard to get - NZ does NOT have mandatory supplementation despite this - only once diagnosed with deficiency under supervision - then given high doses of NON-heme iron which has side effects (GI/nausea/constipation) so compliance rate is low`

Question 48

3 chief functions of iron?

Answer 48

- HB - myoglobin - necessary for the utilisation of energy in metabolic pathways i.e. succinate hydrogenase to ox fat, cytochromes, ribonucleotide reductase, collagen