The Trace Elements

Question 1

How does charge affect bioavailability of minerals?

Answer 1

• absorption of minerals with the same charge may depend on the relative amounts in a meal

Question 2

Amounts of minerals in food maybe depend on…

Answer 2

Where the food was grown

Question 3

Dietary components may enhance or inhibit…

Answer 3

Absorption

Question 4

How is iron absorbed in the diet?

Answer 4

• iron is absorbed from the diet in the heme (animal source) or nonheme (plant sources) form
• charge important in iron absorption; Fe2+ (heme or ferrous form) is more soluble and more easily absorbed than the Fe3+ (nonheme or ferric) form
• consumption of nonheme iron with acids (especially vitamin C) and meats aids absorption

Question 5

Where is iron found in the diet?

Answer 5

• clams, chili beans, beef liver, eggs, liver, kidney beans, lentils, spinach
• protein sources
• milk is a poor source of iron

Question 6

What is the process of iron absorption, transport, and storage?

Answer 6

• heme or ferrous (2+) nonheme iron is absorbed, then converted to the ferric form (3+) by a copper-containing protein in mucosal cells
• some iron is stored in mucosal cells by binding to ferritin, but this is excreted when the cell dies
• transferrin is the protein that carries iron in blood; iron is stored in the liver, bone marrow, myoglobin, and spleen, ferritin-bound

Question 7

What is the function of iron?

Answer 7

• a component of myoglobin and hemoglobin
• part of proteins in the CAC and ETC along with transport for O2 and CO2
• part of catalase, drug-metabolizing enzymes (cytochrome P450), and has immune functions as well

Question 8

Where is iron depleted from first?

Answer 8

• iron stores, then plasma, then RBCs

Question 9

The only way we lose iron is through..

Answer 9

Bleeding (menstruation and pregnancy)

Question 10

What mineral is most likely to be deficient?

Answer 10

• iron

- up to 80% of world’s population is deficient

Question 11

What group is most likely to be iron deficient?

Answer 11

• women and children are most often deficient – women due to menstruation and children due to the increased needs during growth

Question 12

What is microcytic hypochromic?

Answer 12

Small, pale cells because heme group is deficient in RBCs

Question 13

What is iron toxicity?

Answer 13

• iron can be toxic acutely (it’s a common cause of poisoning in children), or built up gradually to cause iron overload
• too much iron encourages ROS

Question 14

Normal hematocrit values?

Answer 14

Men: 0.420 - 0.520
Women: 0.370 - 0.460

Question 15

Normal hemoglobin?

Answer 15

Men: 140 g/L
Women: 123-157 g/L

Question 16

What is hemochromatosis?

Answer 16

• condition where you absorb too much iron
• common genetic defect in the Caucasian population, but it often goes undetected by health care providers
• iron overload can cause oxidative damage leading to chronic diseases and premature death

Question 17

Serum vs. plasma?

Answer 17

• serum is similar to plasma but without clotting factors and platelets

Question 18

How is hemochromatosis treated?

Answer 18

• patients should be advised to watch iron intake, do not take supplements containing iron and have blood checked regularly for ferritin

Question 19

What is the prevalence of inadequate zinc intake?

Answer 19

• high across all age groups, especially older men

Question 20

Where is zinc found?

Answer 20

• zinc is available in meats and vegetables, but is less easily absorbed from plants due to binding by phytates (present in plant foods)

Question 21

How is zinc absorbed?

Answer 21

• zinc homeostasis is controlled in the GI tract - there are protein transport systems for intake and export from the mucosal cells; metallothionein controls the transfer into the blood
• will hold onto zinc in high levels
• metallothionein also binds copper, so high zinc levels can inhibit copper absorption

Question 22

What are zinc fingers?

Answer 22

• common DNA binding motif on proteins, allow the regulation of DNA transcription
• these “fingers” enable binding of proteins to regulatory regions of DNA via cross-linking
• some vitamins, and hormones such as estrogen, testosterone and thyroid hormones bind to zinc finger proteins to regulate gene expression

Question 23

How is copper absorbed?

Answer 23

• copper absorption is affected by high intakes of other minerals (iron, manganese and molybdenum), most notably zinc
• metallothionein, which is induced by high zinc intake, has greater affinity for copper than zinc and can prevent copper’s entrance into the bloodstream
• phytates in foods can actually increase copper absorption by binding zinc
• deficiency uncommon, only seen with TPN

Question 24

What is the role of mineral antioxidants?

Answer 24

• many trace elements function as as antioxidants
• act in different areas to neutralize ROS
• ex. vit E in cell membrane

Question 25

What is manganese?

Answer 25

• Mn is part of superoxide dismutase in mitochondria; also required for enzymes for amino acid, carbohydrate and cholesterol metabolism
• when intake is low manganese absorption increases, absorption decreases when intake is high
• elimination occurs through bile

Question 26

What is selenium?

Answer 26

• Se is part of glutathione peroxidase, it spares vitamin E by reducing the production of free radicals
• deficiency can cause muscle weakness and discomfort, also poor heart function as seen in Keshan disease
• in countries where the food is grown and eaten locally soil content has an impact on the intakes of minerals; in China areas with low selenium are correlated with Keshan disease, areas with high levels showed fingernail changes and hair loss

Question 27

What is iodine?

Answer 27

• iodine is a component of thyroid hormones thyroxine (T4) and triiodothyronine (T3)

Question 28

What is the function of thyroid hormones?

Answer 28

• these hormones regulate protein synthesis, basal metabolic rate, and growth and development by controlling gene expression
• a selenium-containing enzyme converts T4 to T3 in the cell for receptor protein binding to control gene expression
• T3 can enter nucleus

Question 29

How are thyroid hormones regulated?

Answer 29

• thyroid hormone levels are controlled by release of thyroid-stimulating hormone (TSH) from pituitary gland when blood levels are low
• with TSH, the thyroid gland takes up iodine and synthesizes hormones, which feeds back and turns off TSH
• thyroid hormones cannot be produced in absence of iodine; deficiency of iodine results in reduction of metabolic rate with fatigue and weight gain

Question 30

What occurs with iodine deficiency?

Answer 30

• goiter is the result of iodine deficiency, the thyroid gland is enlarged due to continued stimulation of the gland by TSH
• thyroid hormones are needed for growth; stillbirth or spontaneous abortion may occur in pregnancy, cretinism in live births
• goitrogens can cause deficiency, but this is unusual in Canada due to fortification (salt)
• cassava contains goitrogens (turnip and cabbage)

Question 31

What is fluoride?

Answer 31

• fluoride deficiency results in greater numbers of dental cavities
• fluoride has an affinity for calcium, it is associated with calcified tissues
• water is fluoridated for the prevention of cavities, but there is concern about toxicity due to high intakes of fluoride (ingestion of toothpaste)
• too much fluoride can result in pitting and staining of the teeth called “fluorosis”