Nutrition Lecture 10: Iron Flashcards
What are rich food sources of iron?
Meat, pate, some seafood, red kidney beans, fortified foods
What is bioavailability defined as?
The proportion of intake of a nutrient that is absorbed and utilized
What is iron bioavailability influenced by?
- Host-related factors
- Chemical form (haem vs non-haem Fe)
- Enhancers
- Inhibitors
What is the relationship between iron status and iron absorption?
Increased serum ferritin decreases absorption
What host-related factors affect iron absorption
- Pregnancy
- Recent iron intake
- Genetics
- Disease states
What is the absorption of Haem Fe?
25-30%
What is the absorption of Non-haem Fe?
5-15%
Haem vs non-haem iron
- Haem iron absorption is considerably higher
- bigger variability in non-haem iron
What form of iron does meat provide?
Meat doesn’t just provide Haem iron, it provides both
Generally, 90% of iron consumed is…
Non-haem
What are enhancers of iron absorption?
- Vitamin C (ascorbic acid?
- Meat, fish and poultry (not eggs and milk just flesh foods)
What are inhibitors of iron absorption?
- Phytate
- Tannins (tea and coffee)
- Oxalic acid
Where is iron absorption of Haem iron?
Mainly in duodenum
How is Haem iron absorbed?
- Haem split from globin
- Haem absorbed intact
- Ferrous iron released in enterocyte
- Joins common pool in enterocyte with NHFe
Where is iron absorption of non-haem?
Mainly in duodenum
How is non-haem iron absorbed?
- Lumen of the gut has a neutral pH, so will be in ferric 3+ form
- Duodenal cytochrome B reduces ferric form into ferrous form
- Then absorbed through the DMT1
What are the forms of iron in the body?
- Haemoglobin
- Myoglobin
- Enzyme Fe
- Storage Fe
What percent of body Fe is haemoglobin?
67%
What is the function of Haemoglobin?
Transports O2
What percent of body Fe is myoglobin?
4%
What is the function of myoglobin?
O2 storage in tissues
What percent of body Fe is enzyme Fe?
0.2%
What is the function of enzyme Fe?
- Energy metabolism
- Neurotransmitter formation
- Bacterial killing in leukocytes
What percent of body Fe is storage Fe?
27% - depends
Where is Fe stored in the body?
Liver, spleen, bone marrow
How is Fe involved in transport?
Transport Fe is in the form of transferrin (0.1% body Fe)
How is iron excretion controlled?
Its not, all of the control is happening at the absorption step
How is iron lost?
Epithelial cells and Fluids
What epithelial cells lose iron?
- Skin (0.2mg)
- Intestinal mucosal cells (0.1mg)
- Urinary tract cells (0.1mg)
What fluids lose iron?
- Blood in gut (0.4mg)
- Bile (0.2mg)
- MENSTRATION
Men vs Women iron losses per day
Men = 1mg/day
Women = 2mg/day
Why is reutilisation of iron so important?
To form all the erythrocytes needed you would need approximately 30mg per day BUT we only absorb about 1-2mg
Where does majority of iron reutilisation come from?
Old red blood cells in spleen and liver
What are the concequences of iron deficiency anemia?
- Decreased growth
- Behavioural disturbances
- Decreased cognitive function
- Fatigue
- Spoon-shaped nails
What are the consequences of the depletion of iron stores?
Can see same symptoms of anaemia - you are more at risk for anaemia
What groups are at risk of iron deficiency?
- Pre-term infants
- Infants
- Toddlers
- Menstruating women
- Pregnant women
- Blood donors
When is there are high requirement for iron?
- Growth
- Blood loss
- Pregnancy
What is recommended for people with anaemia?
Iron supplements or IV infusion
What is recommended for people with non-anaemic iron deficiency?
Diet, supplements
What is acute iron toxicity?
Unintentional overdose of iron tablets, Lethal oral dose = 200mg/kg
What is hereditary haemochromatosis?
A homozygous genetic condition that causes poor control of iron absorption
What mutation is present in people with hereditary haemochromatosis?
C282Y mutation on the HFE gene
In people with hereditary haemochromatosis, where does iron accumulate?
In liver, pancreas and heart
What is the EAR for iron?
Men = 6mg/day
Women = 8mg/day
What is the RDI for iron?
Men = 8mg/day
Women = 18mg/day
Why is RDI so high for women?
There is a big skew of women, because there is large variety in blood lost during menstruation between women
How does Heme iron enter the enterocyte?
- Comes in through heme transporter
- Is then acted on by the enzyme oxygenase to become non-heme iron
What transporter brings heme iron into the enterocyte?
Heme transporter
What enzyme converts heme iron into non-heme iron once inside the enterocyte?
Heme Oxygenase
What form does non-heme iron arrive at the enterocyte in?
In ferric form (Fe3+)
What enzyme transforms non-heme iron from ferric (Fe3+) to ferrous form (Fe2+)?
Duodenal cytochrome B - this is a reduction step
How is non-heme iron (once transformed into ferrous form) transported into the enterocyte?
Through DMT1
Once inside the enterocyte, what are the two options for iron?
- Stored as ferritin
- Transported out of the enterocyte
How is iron stored as ferritin inside the enterocyte?
In muscosal ferritin
What transporter transports iron out of the enterocyte (it is all in ferrous form)?
Ferroportin 1
What needs to happen to ferrous iron (Fe2+) once it is transported out of the enterocyte?
Needs to be oxidised back to ferric form (Fe3+) - as ferrous form is very reactive
How is ferrous iron (Fe2+) transformed back to ferric iron (Fe3+) outside the enterocyte?
By hephaestin
How is newly transformed Fe3+ iron, out of the enterocyte, transported around the body?
Bound to plasma transferrin
