Bone Health Flashcards
What are the first and second most abundant minerals in the body?
Calcium (1st) and phosphorus (2nd)
What enhances the absorption of calcium?
-mostly absorbed in duodenum where it is transiently acidic; increased solubility
- Calcium absorption depends on active vitamin D present in intestinal cells
- estrogen enhances synthesis of active vitamin D > increased Calcium absorption
- absorption proportional to needs: pregnancy ~50% absorbed; children ~50% absorbed to meet growth needs
- younger people absorb better than the elderly
- lactose enhances Calcium absorption
- % absorbed inversely proportional to intake (i.e., higher intake, lower % absorbed)
What decreases absorption of calcium?
Food Constituents
- high fibre diets ~50+ g/day
- phytic acid in whole grains and legumes and oxalic acid in vegetables (e.g., spinach, rhubarb) -very high fat intake – can lead to steatorrhea (fat in stool)
- vitamin D deficiency
- polyphenols (tea, coffee)
- *Supplement Use**
- high Magnesium, Phosphorus, Zinc or Iron intakes (supplement use) with a low Calcium intake -% absorbed inversely proportional to intake: choose Calcium supplements ≤500 mg/dose
- *Menopause** – lower estrogen
- *Old Age** – decreased stomach acidity, decreased efficiency of absorption
What are the roles of calcium & phosphorus relating to bone health & maintenance?
- dietary Calcium and Phosphorus are essential for bone formation and maintenance
- Ca2+ and Phosphate salts form HYDROXYAPATITE crystals, (a common type of bone crystal), deposited onto the PRO collagen matrix of bone (osteoid); provides strength and rigidity to bones -substitutions in the hydroxyapatite crystal can form other mineral crystals also found in bone
Mg2+, Sr2+, Na+, K+ can replace Ca2+ CO32-, HPO42- can replace PO43-
F- can replace OH
What are the roles of Vitamin D in regards to bone health & maintenance of blood calcium?
- regulates blood calcium and bone metabolism (see Calcium Balance notes above)
- calcitriol acts at 3 sites – intestines, bone, kidneys
- at low blood calcium levels, calcitriol causes increased calcium blood levels
What are the other roles of calcium?
- *Nerve Transmission and Muscle Contraction**
- Sodium-Potassium ATPase pump in nerve cell membrane allows flow of ions (Na+, K+) across the membrane to generate an action potential
- ions flowing into nerve cell permit release of neurotransmitters, substances which allow nerve cells to communicate with each other (e.g., acetylcholine, dopamine, serotonin, antidiuretic hormone) -action potential travels along nerve fibre and stimulates muscle cell
- Calcium flows into muscle cell causing contraction
- when Calcium exits muscle cell, relaxation occurs
- when cellular Calcium falls below normal levels in muscle cells, TETANY (spasmodic relaxation) can occur
- when cellular Calcium rises above normal level, RIGOUR can occur and the muscles can’t relax after contracting
- *Blood Clotting**
- Calcium is essential in blood clotting process leading to the formation of fibrin and a clot
- *Hypertension**
- an inverse relationship appears to exist between dietary Calcium and hypertension
- see a preventive effect at ~1000 mg Calcium/day
- DASH (Dietary Approaches to Stop Hypertension) diet – low fat, high fibre, ~3 g sodium/day
What are the other roles of phosphorus?
- *Fluid Balance**
- major intracellular anionic electrolyte; helps to maintain proper electrical and fluid balance
Blood and Tissue Phosphorus
~15% of all body Phosphorus
-the phosphorus salt, phosphate, is found free in cells and the bloodstream and acts as a BUFFER -Phosphorus functions inside cells as part of:
i. ) very high energy phosphate bonds (ATP)
ii. ) phospholipids in cell membranes and lipoproteins to transport fat-soluble nutrients in the body
iii. ) many enzyme reactions – many B-vitamins become active when a phosphate group is added
(coenzymes needed in energy metabolism)
iv.) DNA & RNA –essential for growth)
What are the other roles of Vitamin D?
- *Regulation of Blood Calcium & Bone Mineralization**
- acts at 3 sites: intestine, bone, kidneys to increase absorption/retention of calcium in the body
- *Immune Function**
- calcitriol is associated with maturation of immune cells
What factors affect risk of osteoporosis?
Age/gender/hormones
Genetics/race
Physical activity
Body weight
Smoking & alcohol
Calcium nutrition and associated nutrients
What is PEAK BONE MASS?
- PEAK BONE MASS - mostly accumulates during teen years, but continues until about 25-30 years of age with adequate Calcium intake and other nutrients, including: Phosphorus, Magnesium, Zinc and Fluoride
- different bones reach PBM at different ages
- as we age, osteoblasts (bone-building cells) become less active and osteoclasts (bone breakdown cells) continue to function, therefore, over time our bones naturally lose density and strength
What is osteoporosis?
- a naturally occurring degenerative bone disease characterized by decreased bone density, increased bone fragility, and increased risk of fractures, usually in the hip, spine and/or wrist
- “silent disease” -a pediatric disease waiting until old age to manifest itself
- building peak bone mass early in life (i.e., through teen and early adult years) can reduce risk of debilitating effects from osteoporosis later in life
Discuss phosphorus deficiency.
Deficiency unlikely; may see neuromuscular, skeletal, hematological, and renal malfunctioning
Discuss vitamin D deficiency in children.
Children–RICKETS disease
- inadequate intake of vitamin D > poor mineralization and shaping of bones, bowed legs, malformed ribs (rachitic rosary)
- infants born with ~9 month stores depending on maternal diet
- breastmilk low in vitamin D
- children at risk, especially when vitamin D intake is low and there is little exposure to the sun -prevalence increasing in Canada
Discuss vitamin D deficiency in adults.
OSTEOMALACIA (“soft bones”) disease
- osteoid = protein matrix secreted by osteoblasts into which minerals are deposited to form bone -osteoid doesn’t mineralize properly and accumulates, making bone soft and not rigid
- see progressive weakness with increasing pain in lower back and legs
Causes:
i. ) kidney, liver, intestinal diseases: decreased absorption of vitamin D; inefficient conversion to active form in liver &/or kidneys
ii. ) low intakes of vitamin D and little exposure to sun
iii. ) closely spaced, repeated pregnancies
Treatment: dietary intake and/or synthesis through careful exposure of skin to the sun
What are the components of bone?
- bones contain nerves, cartilage, connective tissue in addition to mineral crystals in a protein (collagen) matrix known as osteoid
- RBC, WBC, and platelets manufactured in bone marrow (centre of bone structure)
