Minerals and trace elements

Question 1

What is homeostasis?

Answer 1

Homeostatic mechanisms controls the mineral concentration in the body by regulation of: absorption, storage, excretion.

Question 2

Where in the body can you find calcium?

Answer 2

Skeleton (99%) mineralized tissues – hydroxyapatir (Ca10(PO4)6(OH)2) – structure, storage.

Blood, ECF, tissue (~1%) – muscular contraction, transmission of nerve signals, regulation of blood pressure, cofactor to digestive enzymes, blood clotting, the immune system.

Question 3

What are calciotropic hormones and what do they do?

Answer 3

Calciotropic hormones regulates the [Ca2+] in plasma
(1-2 at low [Ca2+)]
1. Parathyroid hormone (PTH)
2. 1,25-dihydroxycholecalciferol [1,25(OH)2D3]

3. Calcitonin – at high [Ca2+]

Question 4

Describe the calcium homeostasis.

Answer 4

From the intestine and kidney via [1,25(OH)2D3] the blood calcium is increased.

From bone, PTH & [1,25(OH)2D3] increase the blood calcium concentration.

Calcitonin decreases the blood concentration and moves the Ca to the bones and kidney.

Homeostatic regulation of serum calcium, showing the integration of hormon action at tissue levels. Th plasma calcium should be at 9-10.4 mg/ 100 ml. If not its regulated.

Question 5

How can calcium be taken up in the intestine?

Answer 5

Via 2 steps.

1. Transcellular – active uptake by mucosal Ca2+ transport protein – calbindin – duodenum, stimulated by vitamin D, saturable
2. Paracellular – passive uptake – all parts of the intestine, concentration dependent.

Question 6

How is calcium absorbed?

Answer 6

Depending of intake, physiologic status and vitamin D status (10-30% is absorbed from mixed diet) Usually good to spread out the intake over the day,

Question 7

What effects the calcium uptake?

Answer 7

Dietary factors:
+ lactose, insulin, low pH,

• phytate (fibrers), oxalic acid.

Question 8

What does calcium deficiency result in?

Answer 8

1. Long term inadequate intake/poor absorption
2. Calcium concentrations maintained at the expenses of skeletal mass
3. Reduced bone mass (osteoporosis)
4. Fractures

Question 9

Describe osteoporosis.

Answer 9

Osteoporosis (porous bones)
Affects the whole skeleton however, special concern are: spine, hip and wrist.
In the spine (vertebrae) – collapse of the spinal bones, back pain – due to pressure, curved back, deformation, loss of height, red. Pulmonary function, immobility, impact of quality of life.

Question 10

What are the major risk factors of osteoporosis and fractures?

Answer 10

low peak bone mass (PBM)/bone mineral density (BMD), genetic factors (particularly hip fracture), diet (adequate levels of calcium and vitamin D), sex hormones (oestrogen), smoking, increasing risk with age, physical inactivity, reduced muscle strength, high intake of alcohol (>4 units/day =40ml or 32 g of pure alcohol can double the risk), nutritional status (under weight/overweight), drugs (corticosteroids, neuroleptics, sedatives)- increased risk of hip fractures.

Question 11

What is the treatment for osteoporosis?

Answer 11

Stop/slow the rate of bone loss: “anti-resorptive” (bisphosphonates), vitamin D, calcitonin, osteoprtegerin (OPG) -> osteoclast cells
Increase formation of new bone mass – parathyroidea hormone (PTH) and fluoride.

Question 12

How can osteoporosis be prevented?

Answer 12

Bone strengthening – weight-bearing exercise (walking and stair climbing). Exercise that enhanced flexibility and balance – studies have shown that e.g. individuals who practice tai chi have 47% decrease in falls and 25% less hip fractures than those who do not. Strengthening of back muscles can reduce risk of fractures in the spine

Question 13

Where in the diet can calcium be found?

Answer 13

Dairy (~75%)

Other important sources are green vegetables, fish, shell-fish, rose hip, berries, nuts.

Question 14

How do you assess the calcium status?

Answer 14

Biochemical indicator, not available. Blood concentration not good indicator (due to homeostatic regulation). Measurements of MBC/BMD (bone mineral content/density) – DEXA

Question 15

What are some magnesium sources?

Answer 15

Magnesium sources: green vegetables, cereals, fish, meat & milk.

Question 16

What are some phosphorus sources?

Answer 16

milk, meat, fish, eggs, cereals & nuts.

Question 17

What is magnesium and phosphorous part of in the body?

Answer 17

In the skeleton, but also involved in several enzymatic steps
Balance regulated by vitamin D, PTH and calcitonin,

Question 18

How is iron distributed in the body?

Answer 18

Oxygen transport – haemoglobin (~60%) and myoglobin (~4-5%)
Iron transport – transferrin (<0.1%)
Tissue enzymes – cytochromes, catalase (~5-7%), (electron transports, immune system)
Storage – ferritin (~5-20%) and hemosiderin (10%)

Question 19

Describe the absorption and recycling of iron

Answer 19

The metabolism of iron. There is a main internal loop with a continuous re-utilization of iron and an external loop represented by iron losses from the body and absorption from the diet.

The internal loop.
Plasma: transferrin iron -> bone marrow: red blood cells precursors -> Circulating red blood cells -> spleen: reticulo-endothelial macrophages -> plasma.

Question 20

What is caused by iron deficiency?

Answer 20

Anameia.

The iron stores is depleted or theres signs of low formation of red blood cell.

A normal iron level consist of: storage iron (ferritin), haemoglobin, serum iron and enzyme iron.

Deficiency/depletion: the storage iron is depleted.

Early anaemia: decrease in transported Fe.

Server anaemia: insufficient prod. of red blood cells.

Question 21

How can iron status be measured and what are some issues regarding iron level measurement?

Answer 21

Serum ferritin (can give high values during infections/infl. Despite deficiency)
Serum iron [S-Fe] – low at iron deficiency
Total iron binding capacity [TIBC] – conc. Of transferrin in plasma, high at iron deficiency
Serum transferrin receptor [S-TfR] (not affected by infection/infl. Status) -increases at iron deficiency
Hemoglobin – shows hemoglobin content in bone marrow. (will not show if there is a deficiency due to losses in iron storage)

Using only hemoglobin measurement will not give enough information for anaemia when having deficiency. The storage is gone but the haemoglobin is still at the same level.

Question 22

What are some symptoms of iron deficiency and anaemia?

Answer 22

Symptoms of moderate to severe iron deficiency and anaemia include: general fatigue, weakness, pale skin, shortness of breath, dizziness, strange cravings for non-food items: such as dirt, ice, clay, tingling or a crawling feeling in the legs, swelling or soreness in the tongue.

Question 23

Were in the diet can iron be found

Answer 23

animal origin: 40% heme 60% nonheme, plant origin: 100% nonheme, total intake from all food 10%heme and 90% nonheme.

Good sources of heme iron: chicken liver, clams, beef liver, beef, turkey leg, tuna, eggs, shrimp, leg of lamb.

Good sources of nonheme iron: cooked soybeans, pumpkin seeds, quino, tomato paste, white beans, cooked spinach, lentils.

Question 24

What are some dietary factors known to influence the uptake of nonheme iron?

Answer 24

Enhancers: meat, fish, shell-fish, ascorbic acid

Inhibitors: phytate(fibres), polyphenols(from tea and coffee), soy protein, calcium?

Question 25

What is the result of excess iron?

Answer 25

Hemosiderosis medical term for iron overload. Hemochromatosis – the most commonly diagnosed iron overload disease (genetic). Resulting in excessive iron absorption in the intestine -> organ damage and organ failure.

Question 26

Why is zinc important?

Answer 26

Zinc dependent enzymes are involved in the metabolism of carbohydrates, protein, lipids and vitamins. Zinc containing DNA-binding proteins belong to a class of proteins called transcription factors, stabilization of cell membranes, important for the immune system, growth, reproduction.

Question 27

Describe absorption and storage of zinc.

Answer 27

The absorption is affected by the dietary composition (can be enhanced by certain organic acids, amino acid and milk) and the individual zinc status. + animal protein (most likely due to an increased solubility), - phytate (the ratio pytate:Zn is important, protein counteracts the negative effect). It is generally assumed that the body has no specific zinc reserve, but zinc can probably be mobilized from the muscles and bones at extreme conditions.

Question 28

Symptoms of zinc deficiency?

Answer 28

Growth restriction/poor growth (delayed bone maturation), impaired immune function and susceptibility to infection, poor wound healing, hair losses.

Question 29

What are some dietary sources of zinc?

Answer 29

Red meat, mussels, dairy products, whole grain cereals, nuts and seeds.

Question 30

Discuss some risk factors with zinc excess and zinc toxicity.

Answer 30

Zinc may accumulate in acute kidney injury, those with haemochromatosis may absorb larger amount of zinc. Various pesticides contain zinc salt. Compounds used to make paints, rubber and dyes may also contain zinc.

Symptoms
Zinc toxicity may be acute or chronic. Acute toxicity (ingesting more than 200 mg/day of zinc) can cause: abdominal pain, nausea, vomiting and diarrhoea, other reported effects – these include gastric irritation, headache, irritability, letharagy, anaemia and dizziness.

Prolonged intake of zinc ranging from 50-150 mg/day can lead to:
Disturbance of copper metabolism, causing low copper status, reduced iron function, red blood cell microcytosis and reduced immune function. It can also lead to reduced levels of high-density lipoproteins and so it has been suggested that excessive zinc intake may be atherogenic. Excess zinc can also affect cardiac function and can impair the pancreatic enzymes amylase and lipase.