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Foundations In Human Nutrition > Micronutrients: Calcium, Magnesium and Iron > Flashcards

Micronutrients: Calcium, Magnesium and Iron Flashcards

1
Q

Name major dietary sources of calcium

A

Milk (including low fat)

Yoghurt

Cheese (most)

Custard, Ice cream

Milk substitutes if fortifies (not organic)

Cereals (white flour if fortified)

Fish with small bones that are eaten, e.g. sardines, white bait

Soya beans

Eggs

Water (unfiltered)

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2
Q

What factors need to be considered when advising sources of calcium

A

Saturated fat intake if advising dairy sources

Non-dairy sources if intolerant to milk

Absorption varies

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3
Q

Explain absorption of calcium

A

Site: mostly jejunum and ileum (some duodenum and colon)

Active transcellular - efficiency of absorption regulated by Vitamin D metabolites

Passive paracellular diffusion

Approximately 30 - 705 dietary Ca absorbed

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4
Q

Name the 2 things that calcium is augmented by and 2 inhibitors of calcium

A

Augmented by:

Lactose

Casein Phospholipids

Inhibited by:

Oxalic acid (forms insoluble compound)

Phytic acid (less potent but higher concentration in lumen)

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5
Q

Explain the nutritional biochemistry of calcium

A

Di-valent cation

Atomic weight = 40

40mg Ca 2+ = 1 mmol Ca 2+

99% of Ca in body exists in bones as hydroxyapatite

Ca10(OH)2(PO4)6

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6
Q

Explain the metabolic role of calcium

A

Bone mineralisation

Blood clotting

Cell signalling

Blood pressure and cardiovascular health

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7
Q

Explain the role of calcium in bone mineralisation

A

Bone weight ~ 60% calcium-rich minerals

Deposited at a rate of ~ 150 mg/day during adolescence

Continual deposition and resorption throughout life ~ 400mg/day exchange with plasma during adulthood

If resorption > deposition = loss of bone minerals and detrimental bone health

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8
Q

Explain the role of calcium in blood clotting

A

In bleeding, blood clot from protein fibrin

Fibrin is formed by a series of cascade reaction involving clotting factors

Ca 2+ plays a role in the activation of intrinsic and extrinsic factor X

Alters blood levels will compromise coagulation

Less than 2.5 mmol/L - reduces clot formation (e.g. risk of continued bleeding)

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9
Q

Explain the role of calcium in cell signalling

A

Cell membranes relatively impermeable to Ca 2+ (Ca 2+ channels)

Ca 2+ in intracellular fluid is low

Sequestered by endoplasmic reticulum (ER)

Release of Ca 2+ by ER lead to cell division, cell motility, contraction, secretion and endocytosis

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10
Q

Explain the role of calcium in regulating blood pressure and cardiovascular risk

A

High intakes of Ca 2+ may be protective

Balance advice to increase with low saturated fat intake

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11
Q

Explain the consequence of calcium deficiency

A

Obligatory losses of Ca 2+ in faeces and urine

If Ca 2+ is not replaced, plasma levels maintained by bone resorption

Prolonged = loss of bone mass

Eventually, osteoporosis

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12
Q

Explain consequences of excess calcium

A

Toxicity = rare

High intake may impair absorption of other minerals (habitual milk drinkers)

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13
Q

Explain requirements from Calcium

A

UK DRVs are lower than USA

RNI 700 mg (men and women 19-50 years)

Actual intake 1000mg (men and women 19-50 years)

Assumes 30% absorption

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14
Q

Explain some factors that promote bone loss and bone maa

A

Positive bone mass:

Weight bearing exercises

Calcium rich diet

Sunshine (Vitamin D)

Resistance exercises

Gender

Bone loss:

Smoking

Alcohol

Menopause

Sedentary lifestyle

Medications especially steroids

Poor calcium intake

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15
Q

Explain public health issues around Calcium

A

Osteoporosis and bone health

Increasing problems especially with ageing population and low levels of activity

Essential to optimise peak bone mass in adolescence

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16
Q

Explain some major dietary sources of Magnesium

A

Green vegetables

Cereals

Legumes

Animal products (not dairy)

17
Q

Explain average intake of magnesium

A

320mg/d for males, 230 mg//d for females - evidence of low intakes of Mg for children ages 11 tp 18 years, adults ages 19 to 64 years and adults 65 years and over

18
Q

Explain absorption of Magnesium

A

Mainly in the small intestine by facilitated diffusion or simple diffusion

40 - 60% of dietary intake absorbed

Excretion via kidneys

Kidneys are very efficient at conserving Mg when intake is low

19
Q

Explain the nutritional biochemistry of Magnesium

A

Di-valent cation

Atomic weight = 24.3

24.3 Mg 2+ = 1 mmol Mg 2+

60-65% of Mg in body exists in bone, 27% in muscles, 7% in other cells, 1% in ECF

20
Q

Explain metabolic rate of Magnesium

A

Intracellular Mg is involved in energy metabolism acting as a cofactor for enzymes requiring ATP

Intracellular Mg is involved in DNA and RNA synthesis - essential for all phosphate-transferring systems

Similar effect to Ca on the excitability of muscle and nerve cells

Involvement with PTH secretion, Vitamin D metabolism and bone function

21
Q

Explain Magnesium deficiency

A

Interrelation between Ca, K and Na - hypomagnesaemia can precipitate hypocalcaemia (MG involved in PTH)

Hypomagnesaemia may cause neuromuscular excitability, increasing cardiac arrhythmias and cardiac arrest

Mg deficiency associated with decreased bone growth, osteopenia and fragile bones

22
Q

Explain the risk of excess Magnesium

A

Hypermagnesemia is uncommon and unlikely from diet alone of normal renal function

Mg supps have been used in pregnancy induced increased BP

Oral Mg supps may prevent constipation (Epsom salts)

23
Q

Explain requirements for Magnesium

A

10.9 mmol/d females (265mg)

12.3 mmol/d males (299mg)

24
Q

Explain major dietary sources of Iron

A

Meat

Cereals

Pulses

Vegetables

Fruit

Egg

Dairy produce

25
Q

What is the percentage of absorption of iron in haem and non-haem

A

Haem: 20-30%

Non-haem: 0.7-23%

26
Q

Explain absorption of Iron

A

No mechanism for excreting Iron

Absorption regulates body iron - if depleted, more absorbed

Duodenum/proximal small intestine

27
Q

Explain dietary implications of foods that contain Iron

A

Promoters:

Meat

Ascorbic
acid

Citric acid

Spices

Inhibitors:

Phytates

Polyphenols

Tannins

Calcium

28
Q

Explain the nutritional biochemistry of Iron

A

Body content = 50mg/mg ~ average man 3.5g

29
Q

Explain the chemical process of Fe 2+ and Fe3+

A

Fe 2+ to Fe 3+ = Oxidation

Fe 3+ to Fe 2+ = Reduction

30
Q

Explain the metabolic role of Iron

A

Oxygen transport

Iron containing enzymes

Immune function

Pro-oxidant activity

31
Q

Explain the role of Iron in Oxygen transport

A

Haemoglobin molecule

Contains 4 haems, each contains one Fe atom

32
Q

Explain what are iron containing enzymes

A

Energy production via oxidative phosphorylation

Cytochromes 9electron carriers) in mitochondria - one Fe atom

Other energy metabolism enzymes e.g. succinate dehydrogenase, NADH dehydrogenase

Catalase, peroxides

33
Q

Explain the role of Iron in immune function

A

Regulator of immune function

Iron is pre-requisite for micro-organism growth

If Iron is within ferritin and transferrin molecules, not available for growth

Also, role in lymphocyte proliferation

34
Q

Name the 2 types of iron-deficiency anaemia

A

Microcytic

Hypochromic

35
Q

Explain the consequences of iron deficiency

A

Tiredness, breathlessness, irritability, poor concentration

Reduced work performance

4-13% of maternal deaths in pregnancy/childbirth

Preterm labour, low birth-weight, infant mortality

School children - reduced motor activity, social inattention, poor school performance

36
Q

Explain consequences of excess Iron

A

Acute e.g. excessive FeSO4

  • Overrides GI tract regulation
  • Free radicals generated
  • Nauseas, vomiting, stomach pain, constipation
  • Metabolic acidosis
  • Cardiovascular collapse

Chronic, e.g, haemochromatosis

  • Gene defect
  • GI tract regulation impaired leading to excessive absorption

Gradual deposition of Fe in soft tissue (liver, heart, pancreases)

Organs damaged by free radicals

Cirrhosis, diabetes, cardiovascular disease, cancer

Treated by regular phlebotomy

Liver biopsy

  • Iron deposited in macrophages

Iron deposited in biliary epithelium

Chronic, e.g. from iron contamination

  • Cooking pots
  • Beer brewed in iron containers
37
Q

Explain dietary requirements for Iron

A

Haem ~ 15% dietary iron but ~ 30% absorbed iron

UK DRVs are lower than USA

RNI Men between 19-50: 8.7mg

RNI Women between 19-50: 14.8

Women requirements are higher than males because 10% of women with high menstrual losses will require more iron

Foundations In Human Nutrition (17 decks)

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