Magnesium

Question 1

RDA=

Answer 1

400mg (M)
310mg(F)

Question 2

do canadians meet the RDA for Mg

Answer 2

No

Question 3

What was the EAR set for

Answer 3

maintain Mg balance

Question 4

T or F: Mg found in only 3 food groups

Answer 4

FALSE: Mg is found in all 4 food groups (F&V, grains, dairy and alt, meat and alt)

Question 5

good food sources of Mg

Answer 5

green leafy veg, nuts, legumes, whole grains

Question 6

why are dark green leafy veg especially good sources of Mg

Answer 6

lots of chloroplasts which produce energy by photosynthesis (Mg is used in over 300 mitochondrial reactions/ energy pathways in chloro)

Question 7

what does refining whole grains do to Mg

Answer 7

refining whole grains reduces Mg by over 75%

Question 8

3 steps of Mg digestion and absorption

Answer 8

1. Mg crosses BBM of enterocyte through Mg channel TRPM6 *Ca is TRYPV6, different
2. Mg may be absorbed between cells/ paracellular diffusion, influenced by electron chemical gradient and solvent drag
3. Mg pumped out of cell across BLM by Na-dependent ATPase

Question 9

inhibitors of Mg absorption

Answer 9

phytic acid
fibers
unabsorbed fatty acids
divalent cations compete

Question 10

two systems of absorption:

Answer 10

1. ACTIVE CARRIER-MEDIATED: (saturable) operates when Mg intake is LOW
2. PASSIVE DIFFUSION: (conc dependent) Mg intake is HIGH

Question 11

percent of dietary Mg typically absorbed?

Answer 11

30-60%

Question 12

Mg Transport %’s in blood

Answer 12

50-55% free Mg+2 ion
20-30% bound to protein (albumin or globulin)
5-15% complexed with anions

Question 13

how do kidneys control Mg losses

Answer 13

in response to plasma concentrations. increase Mg = increase excretion rate of Mg

Question 14

how do bones control Mg

Answer 14

bones provide a reservoir of Mg, plasma conc can be maintained at the expense of bone mineral breakdown

Question 15

how much of body’s Mg is in bones

Answer 15

50-60%

Question 16

what hormones influence Mg balance

Answer 16

PTH (parathyroid hormone)

increase PTH = low Mg levels = decrease excretion of Mg = PTH stimulates Mg reabsorption = more Mg released from bones

high Mg levels = inhibit PTH

Question 17

2 Mg Functions (function 1)

Answer 17

1. Bone mineralization (several forms of Mg)
   - on bone surface so that Mg is readily available for blood exchange
   - a part of crystal lattice that contributes to structural strength and integrity of bones

Question 18

2 Mg Functions (function 2)

Answer 18

2. Enzymatic reactions
   - Mg required for over 300 enzyme reactions
   - structural cofactor (energy, DNA and protein synthesis) needed for proper functioning
   - allosteric activator (change in enzyme conformation/structure) increase affinity and rate

Question 19

clinical signs of hypomagnesemia & causes

Answer 19

• low Mg
• insomnia, muscle tremors, leg cramps
• excessive alcohol, malabsorptive disorders (Crohn’s), poorly managed diabetes, metabolic diseases

Question 20

clinical signs of hypermagnesemia & causes

Answer 20

• high Mg, less common
• lethargy, muscle weakness, respiratory distress
• impaired renal function

Question 21

nutritional signs of chronic Mg deficiency

Answer 21

many conditions:
hypertension, cardiac arhythmias, CVD, T2D, migraines
supplementation trials inconsistent - eat whole foods and variety

Question 22

Mg and Ca absorption

Answer 22

• compete for channels
• high Mg inhibits Ca absorption
  BOTH increased absorption by 1,25D

Question 23

Mg and Ca plasma levels

Answer 23

• when plasma levels are low both signal increase PTH = increase reabsorption in kidneys and bone stores release minerals into blood

Question 24

Mg and Ca intracellular interactions

Answer 24

• compete
• Mg acts to decrease intracellular Ca and competes for binding sites
  -intracellularly Mg and Ca are tightly controlled (muscle contractions, nerves, enzymes)

Question 25

Mg and Ca in cardiac and smooth muscle

Answer 25

- compete - Mg inhibit contraction/antagonist, relax muscle - Ca causes contraction

Question 26

Mg and Ca in intestine

Answer 26

- compete for cation channel too much Ca might decrease Mg absorption

Question 27

Mg and Ca in kidneys

Answer 27

separate processes- no interactions BUT both effected by PTH

Question 28

Mg interactions with other nutrients

Answer 28

inhibit phosphorus absorption influence ICF and ECF potassium balance excretion: urine, depends on plasma conc feces, mostly unabsorbed skin, sweat

Question 29

RDA specifics: 19-30 years

Answer 29

Men: 400mg women and lactation: 310mg pregnancy: 350mg

Question 30

RDA specifics: 31 years and older

Answer 30

Men: 420mg Women and lactation: 320mg Pregnancy: 360mg

Question 31

Mg deficiency common in ...

Answer 31

hospitalized pts bc lack of appetite/food unappealing

Question 32

Mg deficiency in general population

Answer 32

plasma conc may appear normal at expense of tissue conc/health

Question 33

hypomagnesemia metabolic effects

Answer 33

decreased conc of: PTH, Ca, K, Vit D symptoms: muscular, CV

Question 34

factors that contribute to deficiency

Answer 34

inadequate intake excess alcohol use malabsorptive disorders medications uncontrolled diabetes or metabolic syndrome CV disease develops more quickly if Mg deficiency

Question 35

Why is UL for Mg an exception?

Answer 35

based on acute intake, not chronic

Question 36

UL of Mg

Answer 36

350mg from NON FOOD sources (medications, supplements)

Question 37

example of acute Mg intake

Answer 37

drug such as milk of magnesia (500mg/tbsp Mg(OH)2 ) or antacids

Question 38

which forms of Mg are cathartic? Symptoms?

Answer 38

Mg(OH)2 and MgSO4 increased GI transit over 350mg Mg causes diarrhea, nausea, dehydration

Question 39

hypermagnesemia conc and effects

Answer 39

over 4.9mg/dL impaired renal function, produce neuromuscular/cardiopulmonary effects very high blood levels can result in muscular paralysis, cardiac/respiratory failure

Question 40

Mg assessment of nutriture

Answer 40

serum concentrations: low specificity and sensitivity (NOT ACCURATE bc body can maintain serum conc by using tissues or bones) Measure renal excretion: alone or as part of Mg retention (load) test -dose Mg - measure excretion of Mg = what's absorbed

Question 41

why is Mg deficiency a problem for Canadians

Answer 41

enzyme functions and bone health symptoms: CV, metabolic, neurological, general well-being