7.1 Trace Minerals Flashcards
1
Q
How many trace minerals are there and which is the most abundant?
A
- There are at least 12 known important trace minerals.
- Iron, zinc and flouride are the most abundant. Other trace minerals are present in mg or ug quantities only, but have essential roles.
2
Q
What states does iron exist in the body?
A
- Iron exists in 2 interchangeable ionic states in food and the human body Fe2+ (ferrous) and Fe3+ (ferric)
3
Q
What biological functions is iron involved in the body?
A
- Iron is a cofactor to enzymes involved in oxidation reduction reactions
- Involved in cellular energy production, in the TCA cycle, attached to some enzymes, and in electron carrier proteins for the electron transport chain (ETC)
- Most of the bodies iron is found in 2 particular proteins where it is involved in oxygen transport and storage (hemoglobin and myoglobin)
4
Q
What are the steps involved in iron absorption?
A
- Iron in food is absorbed and stored in intestinal wall cells, bound to mucosal ferritin (a protein)
- This transferrin caries the iron from intestinal mucosal cells into the blood
- Transferrin then transports iron to rest of the body
- Most iron ends up in bone marrow for RBC production
- Excess iron is stored in proteins (ferritin and haemosiderin). This is to protect the body from the damaging effects of free iron.
- Bodily iron status can be determined by blood ferritin levels
5
Q
Where is iron lost from in the body?
A
- The intestinal mucosal cells are rich in iron as the transport process from digested food to the blood is slow. Hence loss of these cells (intestinal lining cells) removes iron from the body
- When in excess stays in intestinal cells. They have turnover of few days only, lost in faeces so this is a loss of iron
6
Q
What is the iron storage protein?
A
Hemosiderin is an iron storage protein, when body iron levels become very high. Protects DNA cell lipids and protein form oxidation effect of free iron
7
Q
What are the factors affecting iron absorption?
A
- Main determinant of iron absorption is its dietary form
- Ferric form Fe3+ is poorly absorbed and is reduced to the ferrous form. Fe 2+ in the GI tract by vitamin C or another water soluble antioxidant
- Absorption of the protein bound heme iron is ~25% whereas non-heme is ~5% depending on dietary factors or body iron stores
8
Q
How does haem iron absorption compare to non-haeme iron absorption?
A
9
Q
What are the absorption enhancers for iron?
A
- People who have an iron deficiency become more efficient at absorbing both haem and non haem iron from foods.
- They are factors that can enhance the sensitive to iron absorption, particularly non-haem iron, such as vitamin C and meat, fish, poultry proteins
10
Q
What are the absorption inhibitors for non haem iron?
A
- Some dietary factors bind with non-haem iron, making it unavailable for absorption
- eg; phytates, oxalic acid, fibres, food EDTA, calcium, phosphorus (milk), tannic acid (wine), tea, coffee, nuts
11
Q
What are the causes of iron deficiency?
A
- Poor vitamin C intake
- Poor bioavailable intake (particularly vegans)
- Blood losses from ulcers, GI parasites, blood donation, injuries, menstrual cycle
12
Q
What are the stages of iron deficiency?
A
- Iron stores depleted (Ferritin)
- Transport iron decreases (Transferrin)
- Haemoglobin production falls
- Haemoglobin and haematocrit values measured in full blood examination (FBE) are late indicators of iron deficiency
- Result of iron deficiency is anaemia (small pale red blood cells)
13
Q
How does a normal and anaemic blood cell compare in appearance?
A
14
Q
What happens when there is anaemia?
A
- Severe depletion of iron stores resulting in lowered haemoglobin stores
- Formation of small, pale red blood cells incapable of carrying normal oxygen load from lungs to tissues
- Faltering energy metabolism, followed by fatigue, weakness, headaches, apathy and pallor
- Results in lack of motivation, apathy and restlessness
15
Q
What are the three ways that there can be iron overload?
A
- Body normally absorbs less iron when body stores are full
- Haemochromatosis, a genetic defect can lead to iron overload
- Due to dietary supplements, blood transfusions and rare metabolic disorders
- In haemosiderosis, large deposits of the protein haemosiderin storing excess iron occurs: Symptoms include; fatigue, headaches, irritability, enlarged liver, lethargy, skin pigmentation, joint disease, body hair loss. Condition exacerbated by alcohol consumption
16
Q
What does iron overload cause in the body?
A
- Iron overload can increase the risk of diabetes, heart disease, liver cancer
- Impair glucose metabolism and pancreases overloaded
17
Q
What are the food sources of iron?
A
- Main sources are meat, fish and poultry
- Wholegrains, cereals, legumes, tofu
- Vegetables in particular dark green
18
Q
What are the sources of iron not from food?
A
- Some intake can come from iron cookware and water supply
- Iron supplements but are not as well absorbed as food, best form is ferrous sulphate or iron chelate
- Vitamin C with iron supplements is of no value (already ferrous form)
- Vitamin C helps with absorption by converting insoluble ferric iron to absorbable ferrous iron.
19
Q
Where is zinc found in the body?
A
- Zinc is required as a cofactor for many enzymes. Generally found in conjunction with proteins in food
- All cells in the body contain zinc; most found in bone, prostate gland and eyes
- Muscles make up a large portion of the body zinc though not individually concentrated in zinc
20
Q
What body functions is zinc involved in?
A
- Not easily released into the blood so frequent or constant intake is required
- Involved in immune function, growth and development, essential to the eyes to convert retinol to retinal, for production of retinol binding protein (RBP) for transport and metabolism of vitamin A
- Also essential for taste, wound healing, sperm production and foetal development
21
Q
How does zinc absorption in the body occur?
A
- Mechanism is similar to iron but intestinal mucosa cells can take zinc back from blood as well as deliver it
- Binding protein is called metallothioein or zinc binding protein (ZBP). ZBP binds and stores dietary zinc
- Major portion of zinc is used in pancreas for production of digestive enzymes
- Bodies zinc stores are adjusted by reabsorption or non absorption in the GI tract.
22
Q
How does bioavailability of zinc compare across different foods?
A
- Bioavailability is 4 times higher from meat than fibre rich cereals
- Fibre and phytates in cereals bind zinc.
- Casein in cows milk binds zinc, human milk does not.
23
Q
How is zinc transported in the body?
A
- Major portion is transported in the blood by protein albumin
- Albumin concentration is major determinant of zinc absorption
- During pregnancy and starvation (PEM) there is a lower albumin levels.
• Hence lower zinc uptake
24
Q
What are the uses for zinc in the body?
A
25
Q
How does zinc interact with iron?
A
- Absorption, transport and an excess or a deficiency of one can greatly impact on another.
- Iron and zinc bind to transferrin in the intestinal mucosal cells, for transport into the blood.
- A dietary ratio greater than 2:1 (iron:zinc) impairs zinc absorption.
- Conversely high zinc intake can impair iron absorption.
26
Q
How does zinc loss in the body occur?
A
- As with iron, the body constantly loses zinc
- Skin and hair contribute to loss, as well as seminal fluid in males
27
Q
How can zinc deficiency arise and what does it lead to?
A
- Growing children need much dietary zinc for correct growth and sexual maturation.
- Middle- eastern diets were often low in zinc and high in fibre and phytates
- Zinc deficiency will result in impaired pancreatic and GI function
28
Q
What happens in zinc toxicity?
A
- Chronic intake slightly above RDA can lead to copper depletion and subsequent heart muscle degeneration.
- Acute very high doses (>2g/day) causes vomiting, diarrhoea, exhaustion and possible death.
29
Q
What foods are high in zinc?
A
- Highest in protein rich foods, particularly shellfish, meat, poultry, beans and dairy products.
- Poorly absorbed from cereal grains.
