Calcium, Vitamin D and Bone Health Flashcards
What are bones made of? What are the different parts role?
- 65% mineral crystals (strength and structural support)
- 35% collagen (flexibility)
What does bone mineral density correspond to?
Bone strength
Name the 2 types of bone tissues.
1) Cortical bone (compact bone, 80% of mineral structure)
2) Trabecular bone (lacy bone, 20%)
Describe the cortical bone.
Very dense; part of outer walls of larger bones and main
tissue of small bones
Describe the trabecular bone.
Lacy architecture; ends of long bones, vertebrae, responses readily to hormones
Describe the 3 steps in bone turnover.
1) Bone growth
2) Bone modeling
3) Bone remodeling
Which step in bone turnover determines bone size?
Bone growth
Which step in bone turnover determines bone shape?
Bone modeling
Which step of bone turnover occurs primarily in adulthood and replaces old bone with new bone?
Bone remodeling
Define resorption. What is it associated with?
surface of bones is broken down
- Osteoclasts
Define osteoclasts.
cells that erode the surface of bones
Define formation. What is it associated with?
formation of new bone in resorption pit
- Osteoblasts
Define osteoblasts.
cells that produce the collagen- containing component of bone
What does osteoporosis cause?
- Compressed vertabrae (pain, less mobility)
- Bones susceptible to fractures
What is the prevalence of osteoporosis in Canada?
- 1 in 4 women
- 1 in 8 men
What is the acute care cost for osteoporosis?
20 billion annually
What is another name for type 1 osteoporosis? Type 2?
Type 1: Postmenopausal
Type 2: senile
What is the age of onset of type 1 osteoporosis? Type 2?
Type 1: 50-70 years old
Type 2: 70 years and older
Where are the fracture sites for type 1 osteoporosis? Type 2?
Type 1: wrist and spine
Type 2: hip
Compare the gender incidence of type 1 and type 2 osteoporosis.
Type 1: 6 women to 1 man
Type 2: 2 women to 1 man
What are the primary causes of type 1 osteoporosis?
Rapid loss of estrogen in women following menopause; loss of testosterone in men with advancing age
What are the primary causes of type 2 osteoporosis?
Reduced calcium absorption, increased bone mineral loss, increased propensity to fall
What is the lifetime risk of sustaining a hip fracture in women? Men?
Women: 15%
Men: 5%
What happens to most patients after a hip fracture?
Most are unable to walk unassisted
How should we prevent osteoporosis?
Focus should be placed on maximizing peak bone mass.
Why is insuring maximal skeletal density healthful?
will prolong the time it takes for bone density to fall below the fracture threshold in response to age-related bone losses
Why is physical activity good for bone density? Who does it affect the most?
- Working muscles pull on bone, causing more trabeculae
and bones grow denser - Bones of active people are denser and stronger than sedentary people (weight training)
- Older women and children
Name some risk factors for osteoporosis.
- Older age
- Low BMI
- Heritage
- Cigarette smoking and alcohol
- Sedentary lifestyle
- Female gender
- Maternal history of osteoporosis
- Estrogen deficiency (women), testosterone deficiency (men)
- Lifetime diet inadequate in calcium and vitamin D
Name some protective factors for osteoporosis.
- Younger age
- High BMI
- African American heritage
- Regular weight-bearing exercise
Why does smoking affect osteoporosis?
- Associated with leanness
- Earlier menopause
- Lower postmenopausal
estrogen levels
Why does alcohol affect osteoporosis?
- Can increase urinary calcium excretion
- Associated with lower dairy food intakes
- May be toxic to osteoblasts
What is the treatment for osteoporosis?
- Anti-resorptive agents inhibit osteoclasts (hormone replacements, calcitonin, biphosphonates)
- Anabolic agents to stimulate osteoblasts (PTH)
Define osteopenia.
- Bone mineral density 1–2.5 SD below the mean established for a young normal population
- (T Score: – 1 to – 2.5)
Define osteoporosis.
- Bone mineral density > 2.5 SD below the mean established for a young normal population
- (T Score: >- 2.5)
Name 2 ways to carry-out a bone assessment.
- DEXA (dual energy X-ray absorptiometry)
- Quantitive ultrasound
Who are the players in the bone growth team?
- Protein - collagen
- minerals - Ca, P, Mg, F
Who are the coaches in the bone growth team?
- Vitamin D, parathyroid hormone
- Calcitonin
Who are the assistants/scouts in the bone growth team?
Vitamins A, C, K
Name the 2 types of calcium functions.
- Acute Health
- Chronic Health
Name the functions of calcium in acute health.
Ca as an ion in solution
- muscle contraction
- nervefunction
- bloodclotting
- immunefunction
Name the functions of calcium in chronic health.
Ca as a mineral in bone
- Mineral of bones and teeth - 99% of calcium
- Maintain bone turnover
How is acute calcium regulated?
- Blood Ca MUST be maintained
- excess/lack of blood Ca is a problem of regulation NOT DIET!!!
How is chronic calcium regulated?
low dietary Ca - robs the “bone RRSP” i.e. decreases bone mineralization
What happens when bone mineralization decreases?
- Stunting in children
- Osteoporosis
What is the RDA for calcium for 9-18 year olds, 19 to 70 year olds and 70 or older?
9-18: 1300 mg/day
18-70: 1000 mg/day
70+: 1200 mg/day
Do pregnant women need more calcium?
No increase
What is the tolerable upper intake level for calcium? Why life cycle does it not apply to? Why?
2500 mg/day EXCEPT infants (0-12 months) for whom this value was not determinable
Compare calcium absorption in adults vs childhood, pregnancy and lactation.
Adults: 30%
Childhood, pregnancy, lactation: 50%
Name factors that increase calcium absorption.
- anabolic hormones
- gastric acid (meal)
- vitamin D
- low phosphate intake
- Lactose (in infants only)
Name factors that decrease calcium absorption.
- ageing
- lack of stomach acid
- vitamin D deficiency
- high phosphate intake
- high insoluble fibre diet
- phytates, oxalates
- high protein intake
Name sources of calcium that are well absorbed.
Cauliflower, watercress, brussels sprouts, rutabaga, kale, mustard greens, bok choy, broccoli, turnip greens
Define bioavailibility.
degree to which the particular nutrient from a food source can be utilized
Does the presence of calcium within a food insure that the food is a good source of calcium?
No
Name 3 types of substances that bind to Ca and reduce absorption.
- Insoluble fiber: binds cations
- Phytates: legumes, nuts, and cereals
- Oxalates: spinach, beets, celery, eggplant, okra, berries, nuts, tea, cocoa
What is urinary calcium excretion influenced by?
- Calcium
- Age
- Caffeine
- Dietary sodium
- Dietary protein
What should individuals with hypercalciuria be advised?
To restrict sodium intakes to minimize urinary calcium
Why does dietary protein influence calcium excretion?
Excretion of sulphate from sulphur amino acids
Calcium supplements are useful for who?
Lactose intolerance, milk allergy, vegans
Which calcium supplement is well absorbed? How much?
- Calcium citrate, gluconate, malate, carbonate etc
- 30%
Why are multivitamins not a great calcium supplement?
Mineral interactions decrease absorption
What is the UL for calcium?
2500 mg
Name 2 consequences of calcium toxicity.
- Compromised Iron Status (and other minerals) Ca inhibits absorption
- Kidney stones
How can supplements increase the exposure to contaminants?
If supplements are from bone meal or dolomite
Name sources of vitamin D from the diet.
Fatty fish
egg yolks
liver
milk - fortified
What is vitamin D synthesized from?
From cholesterol
How do you get vitamin D?
10-15 minutes of summer sunlight (UVB rays)
Vitamin D synthesis decreases as a consequence of what?
with age, dark skin, latitude, winter
D3 cholecalciferol is in what kind of foods?
Animal foods
D2 ergocalciferol is in what kind of foods?
Plant foods
Vitamin D synthesis occurs in 3 organs, name them in order.
- Skin
- Liver
- Kidneys
Name 5 functions of vitamin D.
- Required for calcium absorption (calbindin)
- Regulates blood calcium levels
- Stimulates osteoclasts
- Necessary for bone calcification
- New functions: immunity and cell differentiation
How does vitamin D affect calcium in the intestine?
Increase Ca absorption from diet
How does vitamin D affect calcium in the kidneys?
Decrease Ca excretion in the urine
How does vitamin D affect calcium in the bones?
increase Ca release from bone
Rising blood calcium signals the thyroid gland to release what?
Calcitonin
Falling blood calcium signals the parathyroid gland to secrete what?
Parathyroid hormone
What role does calcitonin play in infants and young children?
against the dangers of rising blood calcium that can occur when regular feedings of milk deliver large quantities of calcium to a small body.
Is vitamin D a hormone or a vitamin?
Both
How does vitamin D act as a hormone?
- Travels in the blood
- Activated in the liver and kidneys
- Acts on intestine, kidney, bones
- To increase Ca availability for bone mineralization and remodelling
How does vitamin D act as a vitamin?
- Essential for the diet (specific function and absence results in deficiency)
- We can’t synthesize as much as we need
- Vitamin is activated to a hormone
What does the RDA of vitamin D assume in Canada?
assume that a person’s sun exposure is inadequate
What latitudes receive inadequate sun in the winter?
> 40° N or > 40 °S
What is the RDA for vitamin D in ug/d and in IU?
15 ug/d and 600 IU
How does the RDA for vitamin D change with age?
Increases with age (20 ug/d for >70 years old)
What are the best sources of vitamin D? How is most obtained?
- Fatty fish (salmon, sardines) best sources
- obtained from fortified foods such as milk and margarine
How do vegetarians receive vitamin D?
from the sun, fortified plant-based milks or supplements
Can you consume too much vitamin D from skin synthesis?
Skin synthesis (sun exposure) cannot cause excess vitamin D formation
How can vitamin D toxicity occur? What happens?
- excess supplements or fish oils
- hypercalcemia and calcification of soft tissues, potentially fatal
What is the UL for vitamin D in ug/d? In IU?
100 μg/d and 4000 IU
Does sunscreen affect vitamin D intake?
Yes
Define osteomalacia.
- Vitamin D deficiency in adults
- Decreased CA absorption
- Bone matrix is decreased (defective mineralization)
- Softening of bone (bone pain, hip fracture)
Define rickets.
- Vitamin D deficiency in children
- Growing bones don’t mineralize properly (softening of bone, bowed legs, stunting, teeth probs)
When does osteomalacia occur?
when vitamin D intake is less than 2.5 ug/day
What forms the hydroxyapatite mineral of bone?
Phosphorus and calcium
How does phosphorus affect Ca absorption?
High intake decreases Ca absorption
What are the functions of magnesium?
- Bone structure and regulation of mineralization, vitamin
D metabolism - ATP synthesis
- Blood clotting, muscle contraction (Ca promotes, Mg inhibits)
Which vitamin is a coenzyme to synthesize bone protein?
Vitamin K
What happens during vitamin K deficiency?
Cannot bind minerals
How is vitamin A related to bones?
Bone remodelling, osteoclast activity
How is vitamin C related to bones?
Cofactor for collagen synthesis (organic matrix)
