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Flashcards in Dietary Calcium Deck (25):
1

Ca functions

-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

2

Decreases Serum Ca

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

3

increased serum Ca

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

4

active absorption of Ca

-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

5

Gene regulation by Vit D

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

6

Genes regulated by VDRE

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

7

Ca absorption and habitual intake

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

8

Ca absorption enhanced by

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

Increased phsyiologic demand (preg/adolescence)

----
lactose
gastric acidity
dietary protein

9

Ca absorption impaired by

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)

10

Ca hydroxyapatite stronger/increased in cortical or trabecular?

cortical

11

Bone formation and resorption

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

12

Avg health adult absorbs how much Ca

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

13

Why is preterm infant at risk

-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)

14

Ca supplementation in young children

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

15

When is 30-50% of bone mass accrued?

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

16

During pregnancy and lactation, what requirement of Ca increases?

-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

17

Ca supplements

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

18

Can Ca supplements be harmful?

-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

19

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

-adolescent girls
-older men and women

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

20

Osteoporosis

-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

21

Non-nutritional factors assoc with bone mineral density

-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

22

Nutritional Factors assoc with BMD

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

23

Other minerals

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

24

ideal diet for bone health

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

Limit:
red meat
sweets, sugar
total and unsat fat

(decreased turnover of bone)

25

Prevention strategies to optimize bone density

-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