Micronutrients (Ca,Vit D) and bone health Flashcards
describe bioavailability of minerals
varies with need (different than vit)
what are binders
combines chemically with minerals which prevents their absorption and carries them out of the body with other wastes
describe nutrient interactions of minerals
sodium and calcium
phosphorus and magnesium
presence/absence of a vit/min can affect another’s absorption, metabolism and excretion
high sodium intakes cause both sodium and calcium to be excreted
P binds with Mg in GI tract. High P = limited Mg absoprtion
example of binders
phytates and oxalatates
definition of bioavailability
rate and extent to which a nutrient is absorbed and used
difference between major and trace minerals
major minerals are present in the body in larger amounts. Also needs to be consumed in larger amounts
examples of trace minerals
Iron zinc copper manganese iodine selenium
6 major minerals
calcium phosphorus potassium sulfur sodium chloride magnesium (in decreasing order)
define vitamin
essential organic nutrients required in small amounts
different forms of a vitamin can have different functions and precursors
function as coenzymes
susceptible to degradation in food
what are fat soluble vitamins
D,E,A,K
what are water soluble vitamins
Vit Bs, C
5 B vitamins?
thiamin, niacin, riboflavin, pantothenic acid, pyridoxine
role of B vits?
Thiamin: pyruvate decarboxylation niacin: NAD NADP Riboflavin: FAD FMN Pantothenic acid: CO! in acetyl coa pyridoxine: transamination rxns
2 coenzyme functions?
hormonal (A and D) and antioxidant (C and E)
function of vit A as reinoic acid (hormonal function)
as retinoic acid: cell differentiation
hormonal function of vit D as calcitriol
calcium availability
2 types of bone tissues
cortical (outside bone)
trabecular (inside bone. more metabolically active)
bone composition?
65%mineral crystals: strength and structural support
35% collagen: flexibility
role of mineral crystals:
strength and structural support
role of collagen in bone?
flexibility
bone mineral density corresponds to….
bone strength
describe cortical bone
compact bone
very dense
part of outer walls of larger bones and main tissue of small bones
80% of mineral structure
describe trabecular bone
lacy architecture
end of long bones
vertebrae
responds readily to hormones
20% of mineral structure
3 steps in bone turnover are:
- bone growth
- bone modeling
- bone remodeling
describe bone growth in bone turnover
determines bone size
begins in the womb
continues until early adulthood
describe bone modelling in bone turnover
determines bone shape
begins in womb
continues until early adulthood
describe bone remodelling in bone turnover
maintains integrity of bone
replaces old bone with new bone to maintain mineral balance
involves bone resorption and formation
occurs predominantly during adulthood
what is bone resorption
when surface of bones is broken down
bone resorption when young vs old?
young: high formation. low resorption
old: less osteoclasts which takes away more bone than putting in. (high resorption low formation)
define osteoclasts ( in bone resorption)
cells that erode the surface of bones
what is bone formation
new bone in resorption pit
osteoblasts?
cells that produce the collagen-containing component of bone
describe process of osteoporosis
trabecular thins until completely lost
less matrix = less bone strength and mass
results in compressed vertebrae (pain and less mobility)
bones become susceptible to fractures
prevalence of osteoporosis
1 in 4 women
1 in 8 men
describe type 1 osteoporosis
“postmenopausal osteoporosis”
50-70 years old
loss of trabecular bone
fracture sites: wrist and spine (falling forward or on bum)
gender incidence 6 women to 1 man
primary cause: rapid loss of estrogen in women after menopause. loss of testosterone in men from old age
describe type 2 osteoporosis
“senile osteoporosis”
70 years and older
loss of trabecular and cortical bone
fracture sites: hip (falling sideways or straight back)
gender incidence: 2 women to 1 man
causes: reduced calcium absorption, increased bone mineral loss, increased risk of falling
describe difference between primary causes of type 1 and type 2 osteoporosis
type 1: rapid loss of estrogen (W) and testosterone (M)
type 2: reduced Ca absorption. increased bone mineral loss. increased risk of falling
what type of disease is osteoporosis
pediatric disease
lifetime risk of sustaining a hip fracture in W and M?
15% W
5% M
prevention of osteoporosis
focus on maximizing peak bone mass (get strongest bones possible when developing in children and teens)
insure maximal skeletal density which prolongs the time it takes for bone density to fall below the fracture threshold
what age is peak bone mass reached
how can you have the strongest bones possible?
30 years
have high vit D and calcium to maximize bone growth when growing (before reaching peak bone mass)
why can men reach higher peak bone mass
testosterone
what period does steep bone mass decline occur in women?
menopause
describe loss in bone mass graph in women
peak bone mass at age 30
gradually lose bone mass until menopause
during menopause: steep loss of bone mass
after menopause: gradual decrease
most important factor in bone density?
physical activity: working muscles pull on bone which causes more trabecular bone grow denser
must combine cardio and resistance
want to offset bone loss in older people and stimulate growth in children
risk factors for osteoporosis
old age
low bmi (= low bone density because higher bmi means more work for bones = high bone density)
excess alcohol consumption
sedentary lifestyle
female
inadequate calcium and vit D
how does BMI affect bone density
high bmi = high bone density because need higher mass to carry more weight
how does excess alcohol consumption affect bone density
high alcohol = high urinary Ca excretion
may be toxic to osteoblasts
how doe ssmoking affect bone density
earlier menopause. lower postmenopausal estrogen levels, decreased blood flow to bone
osteoporosis prevention/treatment:
nutrition
physical activity
no smoking, less alcohol
osteoporosis vs osteopenia
osteopenia: bone mineral density 1-2.5 SD below the mean established for a young normal population
T score: 1-2.5
(precursor to osteoporosis. bone mineral density is lower than normal)
osteoporosis: bone mineral density less than 2.5 SD
T score: less than 2.5
What is the T score?
compares to healthy population
what are the 2 methods of bone assessment?
Dual energy x-ray absorptiometry (DXA): measures bone density with a full body scan and low level xray. Recommended for postmenopausal women
Quantitative ultrasound: uses sound waves. measures bone denstiy at heel, wrist, kneecap. recommended for screening
what are calcium functions in acute health?
muscle contractions, nerve function, blood clotting, immune function
Ca as an ion in solution
calcium functions in chronic health?
mineral of bones and teeth (99%), maintain bone turnover
Ca as a mineral in bone
what is the most abundant mineral in the body?
calcium
what happens when the extracellular fluid contains too little calcium?
parathyroid glands release parathyroid hormone
kidneys reabsorb Ca
Ca levels increase
Describe acute calcium regulation
increase/decrease of blood Ca is caused by regulation problems (Not diet problems)
blood Ca must be maintained (can cause tetany/rigor - uncontrolled muscle contraction). low blood calcium does not reflect lack of calcium, but is caused by a lack of vit D or abnormal secretion of regulatory hormones
describe chronic calcium regulation
caused by low Ca intake from diet
causes stunting in children and osteoporosis
how does blood calcium change with diet?
adequate vs inadequate?
with adequate Ca intake, blood calcium remains normal and bones deposit Ca. Result is strong, dense bones
with Ca deficiency, blood Ca remains normal but bones give up Ca to the blood (because Ca bank is in the bones). Result is weak, osteoporotic/osteopenic bones (or lack of growth in children)
someone can be Ca deficient for years, but not notice because blood Ca remains the same. But they will notice later on when older because they are susceptible to fractures
What does calcitonin do?
inhibits activation of vit D when levels are high
function of parathyroid hormone?
stimulates activation of vit D when levels are too low
describe what happens when blood calcium rises
- rising blood signals thyroid gland to secrete calcitonin
- calcitonin prevents calcium reabsorption in kidneys
- calcium absorption in intestines is limited
- inhibits osteoclast cells from breaking down bone. Release of calcium into blood is prevented
- calcitonin is inhibited once blood Ca levels are low enough
describe when blood Ca falls
- parathyroid glands secrete parathyroid hormone
- PTH stimulates activation of vit D
- vit D and PTH stimulates Ca reabsorption in kidneys
- vit D enhances Ca absorption in intestine
- vit D and PTH stimulates osteoclast cells to break down more bone = more Ca is released into the blood
- blood Ca rises = inhibits PTH secretion
current DRI-RDA for Ca in adults (19-70)?
1000mg/d
why are recommendations of Ca so variable?
need more Ca in teens and children for growth.
Need more Ca in 70 and older to maintain bone
RDA of 9-13 and 14-18 years?
1300mg/d
RDA of 70 or older?
1200mg/d
RDA in pregnancy/lactation mothers?
no increase (1000mg)
why don’t pregnant women need more Ca?
they have increased absorption and decreased excretion (body regulated)
small amounts are taken by bones if not enough Ca in diet
What is the UL of Ca?
2500mg/d (except for infants and babies 0-12months. Not determinable.)
what are serving sizes based on?
amount of Ca from milk
how much Ca absorption in adults, children, pregnant mothers?
30% adults
50%children and pregnant
what increases Ca absorption?
anabolic hormones gastric acid (meal) vit D low phospahte intake lactose (in infants only)
what decreases Ca absorption
ageing lack of stomach acid vit D deficiency high phosphate intake high insoluble fibre diet phytates, oxalates high protein intake
What are some foods that have Ca more than 50% absorbed?
less than 5% absorbed?
50: cauliflower, kale, broccoli, bok choy, brussels sprouts
5: spinach, swiss chard, rhubarb
Define bioavailability
degree to which the particular nutrient from a food source can be utilized
What influences urinary Ca excretion?
Ca intake Age caffeine dietary Na Dietary protein (excretion of sulphate from sulphur amino acids)
describe use of Ca supplements
should never be used to displace Ca from diet
useful for people who are lactose intolerant, milk allergy, vegan. (at risk for inadequate Ca intake)
what is the Ca UL?
2500mg
what happens past the Ca UL?
compromised Fe status (Ca inhibits absorption)
kidney stones
vit D toxicity
What is another name for vit D?
cholecalciferol
sources of vit D?
fatty fish, egg yolk, liver, fortified milk
describe synthesis of vit d
from cholesterol
10-15 mins of summer sunlight
decreases with age, dark skin, latitude, winter
—-
steps:
1. 7-dehydrocholesterol in the skin (precursor made from cholesterol) becomes previt D3 from UV rays
2. becomes vit D3 (inactive)
3. foods also become inactive vit D3
4. in the liver: inactive vit D3 is hydroxylated into 25-hydroxy vit D3
5. in the kidneys: becomes 1,25-dihydroxy vit D3 (active form)
functions of vit d
required for Ca absorption (calbindin)
regulates blood Ca levels
stimulates osteoclasts
necessary for bone calcification
immunity and cell differentiation
actions of vit D in intestine, kidney, bone?
intestine: increase Ca absorption from diet
kidney: decrease Ca excretion in urine
bone: increase Ca release from bone
how does vit D act as a hormone?
travels in blood
activated in and acts on liver and kidneys
increases Ca availability
how does vit D act as a vitamin?
- it’s essential in the diet (has a specific function and absence causes deficiency)
- we can’t synthesize as much as we need
- activated to a hormone
what is the RDA of vit D?
15 ug/d (600 IU)
assumes adequate sun exposure
increases with age (20ug/d for over 70 years)
what is the RDA for over 70 years?
20ug/d
sources of vit D?
most foods have little vit D
fatty fish are best sources
vit D is best obtained from fortified foods
what happens with too much vit D consumption?
results in hypercalcemia and calcification of soft tissues
can’t be caused by too much sun exposure. but can occur from excess supplements/fishoils
vit D UL?
100micrograms/d (4000 IU)
vit D deficiency?
osteomalacia and rickets
- osteomalacia occurs with less than 2.5 ug/day.
decreased Ca absorption
bone matrix is lost = bone pain = hip fracture risk - Rickets.
vit D deficiency in children = bones don’t grow properly.
results in stunting, softening of bone, bowed legs, teeth problems.
prevalence decreased due to milk fortification
what are the roles of phosphorous in the body?
importance in the body?
found in all body cells as a major buffer system (phosphoric acid and salts).
Part of DNA and RNA. Thus necessary for all growth
roles:
- assists in energy metabolism.
- many enzymes and b vits are active only when phosphate is attached
- ATP uses phosphate groups
- lipids use phosphorus as part of their structures (ie. phospholipids which are important components in cell membranes)
- proteins (ie. casein in milk. has phophoproteins)
what does phosphorous for with Ca?
what happens with high intake of P?
P + Ca forms hydroxyapatite mineral of bone
high intake decreases Ca absorption
role of magnesium in the body?
- bone structure and regulation of mineralization
- vit D metabolism
- blood clotting
- muscle contraction (Ca promotes, Mg inhibits)
- acts on soft tissue cells (part of protein making machinery)
- necessary for energy metabolism (ATP synthesis) and enzyme systems
what is the role of Ca and Mg in muscle contractions and blood clotting?
Ca promotes
Mg inhibits
interaction of Ca and Mg regulates blood pressure and lung function
Vit K role?
co-enzyme synthsize bone protein
deficiency of vit K
cannot bind to minerals
role of vit A
bone remodelling, osteoclast activity
role of vit C
cofactor for collagen synthesis
