Examining Micronutrients in the Diet: Iron Flashcards
What is iron?
Trace mineral = <100mg/day
Binds oxygen, nitrogen and sulfur
7 Guiding Questions
What is it?
Why is it important?
How much do we need?
How do we get it?
How is it absorbed?
How and where is it stored?
How do we use it and lose it?
Why is iron important?
Most common nutrient deficiency.
Critical for oxygen transport.
Hemoglobin and myoglobin is 66% of body’s iron.
Functions of Iron
Component of proteins and enzymes.
-cytochromes
Erythrocyte production requires iron.
How many heme groups make up iron?
Four heme groups.
Lots of hemoglobin molecules/groups inside a red blood cell.
How much iron do we need?
It depends on age, life-stage, gender, physical activity level, clinical conditions.
Upper Limit for Iron
Males and females 19-30 years old = 45 mg/day.
Was once the most common poison death in children <6 years due to pill bottles not being child proof at one point.
How do we get iron?
Animal sources = liver, clams, oysters, beef, shrimp, pork, ham.
Plant sources = fortified cereals, oatmeal, chickpeas, spinach, beans.
How is iron absorbed?
Transferrin is held inside enterocyte where it is released into small intestine and binds to iron molecules which in turn binds to cell proteins.
Cell protein takes transferrin-iron molecule to cell wall where it is engulfed and brought back into the enterocyte (endocytosis).
Once inside the cell, transferrin-iron bound to the receptor protein releases where it goes the side of the enterocyte that goes into the hepatic portal circulation.
-no definitive ways of how iron gets into the hepatic portal system.
Regulation of iron absorption (Transferrin)
Iron bound to transferrin is available for transport across the basolateral membrane.
Iron bound to ferritin is unavailable for absorption and is lost into the lumen when the cell desquamates.
-helps regulate how much iron is released into the body and helps get rid of excess iron
-storage/holding tank for iron
Factors influencing iron absorption…
1) Iron Source
2) Gastric Acid Production
3) Iron Status
4) Dietary Factors
1) Iron Source
Heme iron from flesh foods = 10-35% absorbed.
Non-heme iron from plants = 2-10% absorbed.
Cast-iron cooking can increase iron intake.
RDA for vegetarians are 1.8 times higher than for people who eat meat.
2) Gastric Acid Production
Gastric acid enhances iron absorption by…
-releasing iron from non-heme sources
-decreasing pH in the proximal duodenum which increases absorption
However gastric acid production decreases with age and antacids lower iron absorption (increases pH).
3) Iron Status
Iron status is inversely related to iron absorption.
Low iron status can increase absorption to 40%.
-iron deficiency
-menstruation
-pregnancy
4) Dietary Factors
More used for clinical conditions.
Non-heme iron absorption enhanced by vitamin C and meat protein factor (MPF) in heme iron sources.
Iron absorption reduces by phytates (legumes, rice, and whole grains), polyphenols (coffee and tea), soy protein, calcium (Zn, Mg too), and reduce stomach acids (antacids).
How and where is iron stored?
A small amount (<5g) stored in the body.
Stored in intestinal mucosa, liver, bone marrow, and spleen.
Regulation of iron absorption (hepcidin)
Hepcidin is secreted to regulate iron absorption from the liver.
More hepcidin = prevents iron absorption.
Most likely a connection between hepcidin and ferritin.
-hepcidin helps keep ferritin in check
Less hepcidin = increase iron absorption
Up-regulate and down-regulate hepcidin to maintain iron hemostasis.
Hemochromatosis is a genetic disorder where hepcidin is down-regulated and more iron is absorbed leading to damage to some structures.
Hepatitis C suppresses the body’s production of hepcidin.
How do we lose iron?
Feces
Blood (mesturation)
Sweat and blood
Loss of iron through feces…
Iron losses from duodenum.
Enterocytes shed iron every 3-6 days.
Protects us from toxicity.
Loss of iron through blood (mensturation)…
Women lose 15-30mg of iron.
Amenorrhea = cessation of menses due to strenuous activity, low body fat, and bone losses occur.
Loss of iron through sweat and blood…
Distance runners lose iron in sweat.
Iron losses in the blood from foot strike hemolysis and GI bleeding from sheering that occurs when running for long periods of time.
Checking Iron Status
Serum ferritin concentration.
Test before supplementation because excessive iron is toxic.
-liver disease, heart, and joint damage.
Ferritin is a Protein
Stores iron.
Release it in a controlled fashion.
Anemia (without blood)
Genetic disorders include sickle cell anemia and thalassemia.
Iron-deficiency anemia not the same as iron deficiency.
Iron-Deficiency Anemia
Small red blood cells with low hemoglobin.
Clinically classified if hemoglobin <12 g/dL
Iron Deficiency
Stage 1 = decreased iron stores, reduced ferritin level, no physical symptoms.
Stage 2 = decreased iron transport, reduced transferrin, reduced production of heme, physical symptoms include reduced work capacity.
Stage 3 = iron deficiency anemia, decreased production of normal red blood, reduce reproduction of heme, inadequate hemoglobin to transport oxygen, symptoms include pale skin, fatigue, reduced work performance, impaired immune and cognitive functions, etc.
Centrifuged Blood Sample
Produces three layers which include plasma, buffy coat, and hematocrit (red blood portion).
Someone with anemia will have lower hematocrit.
Endurance Athletes at Risk
Who follow restrictive diet.
Experience hematuria (blood in urine)
Menstruating
Training at altitude.
Bottom Line with Iron
Excess iron intake can be dangerous for children, and middle-aged, male, heavy red meat eaters.
Some populations may want to assess iron status include vegetarians, vegans, athletes, adolescent girls, and pregnant women.
