Micronutrients: Calcium, Magnesium and Iron Flashcards
Name major dietary sources of calcium
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)
What factors need to be considered when advising sources of calcium
Saturated fat intake if advising dairy sources
Non-dairy sources if intolerant to milk
Absorption varies
Explain absorption of calcium
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
Name the 2 things that calcium is augmented by and 2 inhibitors of calcium
Augmented by:
Lactose
Casein Phospholipids
Inhibited by:
Oxalic acid (forms insoluble compound)
Phytic acid (less potent but higher concentration in lumen)
Explain the nutritional biochemistry of calcium
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
Explain the metabolic role of calcium
Bone mineralisation
Blood clotting
Cell signalling
Blood pressure and cardiovascular health
Explain the role of calcium in bone mineralisation
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
Explain the role of calcium in blood clotting
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)
Explain the role of calcium in cell signalling
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
Explain the role of calcium in regulating blood pressure and cardiovascular risk
High intakes of Ca 2+ may be protective
Balance advice to increase with low saturated fat intake
Explain the consequence of calcium deficiency
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
Explain consequences of excess calcium
Toxicity = rare
High intake may impair absorption of other minerals (habitual milk drinkers)
Explain requirements from Calcium
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
Explain some factors that promote bone loss and bone maa
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
Explain public health issues around Calcium
Osteoporosis and bone health
Increasing problems especially with ageing population and low levels of activity
Essential to optimise peak bone mass in adolescence
Explain some major dietary sources of Magnesium
Green vegetables
Cereals
Legumes
Animal products (not dairy)
Explain average intake of magnesium
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
Explain absorption of Magnesium
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
Explain the nutritional biochemistry of Magnesium
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
Explain metabolic rate of Magnesium
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
Explain Magnesium deficiency
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
Explain the risk of excess Magnesium
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)
Explain requirements for Magnesium
10.9 mmol/d females (265mg)
12.3 mmol/d males (299mg)
Explain major dietary sources of Iron
Meat
Cereals
Pulses
Vegetables
Fruit
Egg
Dairy produce
