Dietary Calcium

Question 1

Ca functions

Answer 1

-Ca hydroxyapatite: bone, teeth (99%)
-Metabolically active extracellular Ca (1%)
signal transmission (most common)
tertiary structure: activate catalytic and mechanical properties
Clotting, nerve impulse transmission/relaxation, mediation of hormones, growth factors

Question 2

Decreases Serum Ca

Answer 2

increase PTH: increase bone resoption of Ca, decrease Ca excretion, increase phosphate excretion

increase Vit D hydroxylation in kidney: increased Ca intestinal abs, decreased excretion in urine

Question 3

increased serum Ca

Answer 3

-increases Calcitonin (deposition of Ca into bone)
decreased PTH
decreased Ca reabsorption in ascending loop of henle

Question 4

active absorption of Ca

Answer 4

• 3 steps:
  1. apical membrane absorption (TRPV6 protein in duodenum)
  2. Ca in enterocyte transported to basolateral membrane (Calbindin)
  3. out of enterocyte into blood: ATP dependent Ca export; PMCA

*Vit D regulated

Question 5

Gene regulation by Vit D

Answer 5

1,25 OH Vit D3 serves as gene transcription regulater

• if cell expresses Vit D receptor, VDR dimerezes with RXR and bind to Vit D response element (VDRE)
• • serves as upregulator of gene trancription

Question 6

Genes regulated by VDRE

Answer 6

basolateral memb import:
TRPV6 and TRPV5
Cytosolic trans:
Ca BP-9K
CaBP9K and 28K

Apical membrane export:
PMCA 1b
PMCA 1b

Top: duod
bottom:distal nephron

Question 7

Ca absorption and habitual intake

Answer 7

-Ca upregulates absorption percentage with lower intake of Ca to compensate

Question 8

Ca absorption enhanced by

Answer 8

Vit D: synthesis of Ca-transport proteins in proximal small intestine

Increased phsyiologic demand (preg/adolescence)

lactose
gastric acidity
dietary protein

Question 9

Ca absorption impaired by

Answer 9

Vit D deficiency
Steatorrhea (fat malabsorption): unabsorbed FA binds Ca2+, forming Ca based “soaps”

Gastric alkalinity
oxalic acid (spinach)
phytic acid
caffeine (increase urine Ca)
dietary protein (increase urine Ca)

Question 10

Ca hydroxyapatite stronger/increased in cortical or trabecular?

Answer 10

cortical

Question 11

Bone formation and resorption

Answer 11

• PTH and 1,25 vit D increase bone resorption by activating osteoclasts
• formation: osteoblasts form a matrix to replace resorbed bone with new bone

Question 12

Avg health adult absorbs how much Ca

Answer 12

25%
Fetus: 80% in 3rd tri
May decrease in elderly (decreased Vit D, decreased gastric acidity)

Question 13

Why is preterm infant at risk

Answer 13

• hard to match high level of Ca transfer that would occur in utero (330 mg/d at 35 weeks)
• can get osteomalacia of prematurity (deficits of bone mineralizaiton)

Question 14

Ca supplementation in young children

Answer 14

-increase in skeletal size and mineralization, but fail to show consistently that BMC is retained over the long term

Question 15

When is 30-50% of bone mass accrued?

Answer 15

• adolescents (calcium absorption and retention highest in early puberty; slower bone mineralization throughout adolescence)
• peak bone mass at 30 y
• menopause: decrease

Question 16

During pregnancy and lactation, what requirement of Ca increases?

Answer 16

-physiological but not dietary requirements increase.

Pregnancy: Ca abs increases to meet fetal demand

Lactation: PTH increases and bone mass lost, but recovered post weaning

Question 17

Ca supplements

Answer 17

Calcium carbonate (best absorbed with meals)
Calcium citrate (best absorbed between meals)
43% of americans take Ca supplements

Question 18

Can Ca supplements be harmful?

Answer 18

• increased risk of MI ~30%
• Dietary Ca not associated w/ increased risk
• too much supplementation esp for those who do not need it may be harmful

Question 19

Ca needs not being met in which pops? high risk groups?

Answer 19

• adolescent girls
• older men and women

High risk groups?
premature infants
adolescents
peri-menopausal women
[bariatric surgery pts]

Question 20

Osteoporosis

Answer 20

• reduction in bone mass associated w/ impairment in bone structure; increased fracture risk
• loss of height and distorted body shape

25% of women over 50 develop osteoporosis
Fractures often lead to institutionalization

Question 21

Non-nutritional factors assoc with bone mineral density

Answer 21

• genetics (70-80% of peak bone mass driven by genetics)
• initial bone mineral density
• hypogonadism (esp decreased estrogen)
• age
• meds (esp corticosteroids): glucocorticoids, chronic illness, magnitude of steroid use
• behaviors/lifestyle (tobacco, alcohol; opposite (positive) effect with weight bearing exercise

Question 22

Nutritional Factors assoc with BMD

Answer 22

-lifetime Ca intake
-Vit D
-caffeine
-protein
-sodium intake (increased Ca in urine)
Vegetarian diet (decreased Ca in urine)

Question 23

Other minerals

Answer 23

phosphorous
Mg (can give hypoparathyroid)
Vit C (collagen)
Vit K (cofactor with osteocalcin)

Question 24

ideal diet for bone health

Answer 24

DASH
-fruit/veg
low fat dairy
whole grains
poultry, fish, nuts

Limit:
red meat
sweets, sugar
total and unsat fat

(decreased turnover of bone)

Question 25

Prevention strategies to optimize bone density

Answer 25

• achieve peak bone mass when possible (childhood and esp adolescence)
• dietary focus: Ca, Vit D, Vit K, protein, decreased Na
• Maintain ovulation/regular menses
• weight bearing exercise
• avoid: smoking/alc/steroids
  supplement: judiciously when necessary