21 - Iron Flashcards
What is a summary of the role of iron?
Iron is a co-factor for many proteins and is involved in many important cellular functions
Iron overload?
Haemochromatosis. Common - 1/3 in NZ
What are the MAJOR minerals?
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
What are the trace minerals and how much of them do we need?
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
Is iron a major or trace mineral?
trace
What is the most common deficiency in the world?
IRON deficiency
What are 6 functions of iron in the body?
In…
- haemoglobin - blood protein has heme iron that enables O2 transport
- myoglobin - O2 delivery to tissues
- cytochromes - assists in electron transfer and storage of energy through redox reactions of iron (Fe2+>Fe3+)
- ribonucleotide reductase - DNA production
- succinate dehydrogenase - FA oxidation
- collagen synthesis
Since iron is so important why do we only need a trace amount in our diets?
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.
How big are the body stores of iron
1g
What is the daily intake of iron?
1-2mg and daily intake and daily loss of iron equal each other as we are constantly recycling the iron in our body
What is the bioavailability of iron like?
LOW but variable depending on physiological factors i.e. during pregnancy and growth RBC production increases, and dietary factors
What are the steps in iron recycling?
- Bone marrow incorporates iron into the HB of RBCs and stores excess as ferritin
- Carries O2 in blood
- Lost in bleeding
- Liver/spleen breakdown RBCs and recycle iron packaging it into transferrin and excess as ferritin
> excess stores can damage liver (haemochromatosis) - LITTLE lost as sweat and urine
- Transferrin transports iron in blood to BM to be packaged into RBCs or to muscle as myoglobin
How is iron always found in the body and why is this beneficial?
bound to a protein - transferrin and ferritin acts as biomarkers for assessing iron status
Where does most of the absorption of iron occur?
DUODENUM
How is iron stored when we eat it?
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)
Who may have iron absorption problems?
- surgery i.e. bilroth 1 or 2 for cancer and peptic ulcers
- issues with enterocyte integrity (celiacs)
- malabsorption
- SI removed
Heme iron?
- 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
Non-heme iron
- 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+
What is bioavailability of iron dependent on?
It is different depending on amount of non heme and heme we eat
What is on the BL membrane on the enterocyte?
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
what hormone from the liver regulates iron movement out of the cell and into the blood?
Hepcydine
Describe how iron is tightly regulated
Always bound to a protein and stored if not needed - don’t have free iron floating around in body and is continuously recycled
What happens to iron once it is released from intestinal cells?
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
2 ways iron gets into blood?
Release from enterocytes via dietary intake
Breakdown of RBCs by macrophages
Compare heme and non-heme iron
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
Why is non-heme iron not absorbed as easily
- 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
What 5 things ENHANCE non-heme absorption/make it more bioavailable at the enterocyte level?
- MFP (meat factor protein)
- vitamin C (strongest enhancer)
- HCl from stomach - helps solubilise and make more bioavailable
- lactic acid
- sugar
What 6 things INHIBIT non-heme absorption/less bioavailable?
- fibre
- oxalates (BIND non-heme iron - spinach, strawberries, rhubarb
- calcium
- phosphorus
- tannin
- polyphenols
What 3 foods have the highest amounts of iron?
- spinach (but non-heme so not absorbed well at all)
- red meat/steak
- chicken
Besides food what are other sources of iron?
- supplements with vit C
- contamination iron; contamination of cooking vessels into food. Intervention used in populations at risk of deficiency
What needs to be provided with iron supplements to aid bioavailability
Vitamin c as it is non-heme
What are the RDIs of iron?
very variable
The recommended intake of iron depends on the physiological ages and stages of growth
What populations are at risk of iron deficiency/have increased requirements
- 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
Vulnerable groups
infants
toddlers
adolsents esp menstruating females
pregnant women
What are the 3 stages of iron deficiency?
- Depleted iron STORES
- Iron restricted erythropoiesis
- Iron deficiency anaemia
Depleted iron stores?
- 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
Iron restricted erythropoiesis?
- 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)
Iron deficiency anaemia?
- 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
What does iron deficiency look like
microcytic anaemia - pale and small RBCs
Produces the SAME symptoms as folate/B12 deficiency
What else can you measure to help diagnose iron deficiency ?
MCV will decrease
What percentage of children 0-4 have iron deficiency world wide?
43% - very common
higher in developing countries
What do they do in countries where iron deficiency is very prevalent?
interventions like the micro-nutrient sprinkle
education campaigns
Do we have mandatory fortification of iron?
no it is mandatory. We only pick up iron deficiency by screening
In what ethnicity groups of adolescents is iron deficiency more common?
Maori and pacific compared to NZ European (15%)
iron is vital for …. and …
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
What are 4 problems that can occur for in infants due to iron deficiency? And what does this mean for clinical practice?
- irreversible effects in cognition and brain development
- myelination
- neuron growth and differentiation
- neurotransmitter regulation
Means we need to screen and detect iron deficiency in early life before this irreversible problems occur
Pregnant women and iron?
- 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`
3 chief functions of iron?
- HB
- myoglobin
- necessary for the utilisation of energy in metabolic pathways i.e. succinate hydrogenase to ox fat, cytochromes, ribonucleotide reductase, collagen
