KIN275 Introduction to Nutrition (Module 11) - Bone Building Nutrients PDF

KIN275 Introduction to Nutrition Module 11 Bone Building Nutrients Julia Totosy de Zepetnek, PhD Module 11 Learning Objectives 1. Discuss bone cell types & bone growth 2. List the major physiological functions of the bone building nutrients (calcium, phosphorus, magnesium, fluoride) Discuss osteopor...

KIN275 Introduction to Nutrition Module 11 Bone Building Nutrients Julia Totosy de Zepetnek, PhD Module 11 Learning Objectives 1. Discuss bone cell types & bone growth 2. List the major physiological functions of the bone building nutrients (calcium, phosphorus, magnesium, fluoride) Discuss osteoporosis Bone Matrix Inorganic component: 2/3 of bone mass – Ca3(PO4)2 (calcium phosphate) interacts with Ca(OH)2 (calcium hydroxide) to form crystals of Ca10(PO4)6(OH)2 (hydroxyapatite) – As crystals form, they incorporate other calcium salts, e.g. CaCO3 (calcium carbonate), and other ions, e.g. sodium, magnesium, fluoride, phosphate, vit D & K Organic component: 1/3 of bone mass – Mainly collagen fibers (90-95%) – Several materials secreted by osteoblasts (bone cell) Bone Matrix Inorganic: 2/3 bone mass o Hydroxyapatite Organic: 1/3 bone mass o Several materials secreted by osteoblasts; mainly collagen fibers (90-95%) Collagen fibers provide organic framework for hydroxyapatite crystal formation Four types of cells found within bone matrix/tissue Bone Tissue Cells Differentiate between the main function of the 4 bone tissue cell types Osteoblasts Osteocytes Osteogenic cells Osteoclasts Responsible for forming new bone and is found in the growing portion of the bone Differentiated from osteoblasts into osteocytes and maintain bone tissue Undifferentiated Perform bone highly mitotic cells resorption that divide and develop into osteoblasts Types of Bone Compact bone --> parallel osteons – a.k.a. dense bone, cortical bone – Protect, support, resist stress – Sturdy protective layer that surrounds medullary cavity Spongy bone --> trabeculae – a.k.a. cancellous, trabecular bone – Support and storage of marrow – Open network of struts and plates that resembles latticework Bone Remodeling 1/5 skeleton recycled and replaced each year (differs regionally and locally) Bone Remodeling Bone Remodeling Replaces matrix, leave bone unchanged; or Change shape, internal architecture, mineral content Wolff’s Law: bone will grow or remodel in response to forces/demands placed on it During childhood and teenage years, bone formation exceeds bone resorption o Bones become larger, heavier, denser Building Bone Childhood and adolescence are most critical periods of skeletal mineralization Amount bone accrued during growing years is an important risk factor for fractures later in life Although family history, genetic heritability, sex, and race are the main factors that affect peak bone mass, diet and physical activity are responsible for up to 25% of peak bone mass Saskatchewan Pediatric Bone Mineral Accrual Study Peak bone mass usually reached between 20 and 30y – Earlier in females (related to timing of pubertal growth and closure of epiphyses) After achieving the peak bone mass, ongoing bone remodeling usually leads to cortical and trabecular bone loss over time in both sexes – Loss is varied in weightbearing and non-weightbearing bones Goal: accrue as much bone as possible to achieve the highest peak bone mass possible… this will keep you above the fracture zone longer Peak Bone Mass & Bone Loss Module 11 Learning Objectives 1. Discuss bone cell types & bone growth 2. List the major physiological functions of the bone building nutrients (calcium, phosphorus, magnesium, fluoride) Discuss osteoporosis Bone Building Nutrients § Vitamins A, D, K, C § Calcium (Ca) § Phosphorus (P) § Magnesium (Mg) § Fluoride (F) Certain nutrients, when taken in excess, may have a negative effect on bone: vitamin A, sodium, oxalates, caffeine, alcohol – Vitamin A helps produce bone cells needed for growth [required for bone remodeling] – Too much Vitamin A also results in bone loss and increased risk fracture When deficient in certain nutrients, may have a negative impact on bone quality: vitamin D, vitamin K, omega-3, calcium, phosphorus, magnesium, fluoride ll a c Re Major vs. Trace Minerals Not due to relative importance – only named for amounts in diet and amounts stored in body Major minerals Trace minerals Needed in the diet in amounts greater than 100 mg/day, or Present in the body in amounts greater than 0.01% of body mass Required in the diet in amounts of 100 mg/day or less, or Present in the body in amounts of 0.01% of body mass or less Bone Building Minerals Bone Building Nutrients § Vitamins A, D, K, C § Calcium (Ca) § Phosphorus (P) § Magnesium (Mg) § Fluoride [F] Accounts for 98% of the body’s mineral content by weight – 99% of the calcium, 60% of the magnesium and 85% of the phosphate are located in bone matrix Calcium and phosphate combine to form calcium phosphate that makes up the hard bone matrix of bones and teeth; magnesium helps strengthen it Calcium (Ca) Calcium Many roles of Calcium… Involved in: – Blood clotting – Nerve impulse transmission – Blood pressure regulation Activates (binds) calmodulin (cell messenger that reduces BP) – Hormone regulation (PTH, calcitonin) More in a moment! Calcium Most abundant mineral in the body Necessary for bones/teeth 99% of Ca is in bones & teeth as hydroxyapatite Ca10(PO4)6(OH)2 or fluoroapatite Ca5(PO4)3F – (difference is in no. of P groups; fluoride adds strength to teeth) Calcium Calcium & Bone Skeleton contains 1100-1500g Ca – Massive amount of Ca in bone – 1 cm3 of bone contains more Ca than that circulating in blood Amount in blood is crucial Very tightly controlled in the blood (+/- 10%) – ↑ 30% --> neurons / muscle cells unresponsive – ↓ 30% --> convulsions – ↓ 50% --> death Calcium Hormones and Bone Tissue Regulate blood Ca levels Calcium Calcium Calcium Calcium Summary: Hormones & Blood Ca Bone cell action is under the control of hormones & other bone cells Parathyroid hormone (PTH) – Secreted from parathyroid gland – Stimulates osteoclast/blast activity; increases [blood Ca2+] Calcitriol (active form of Vitamin D3) – Produced in the kidneys – a.k.a 1,25 dihydroxyvitamin D3 – Essential for normal calcium and phosphate ion absorption in digestive tract Calcitonin – Secreted from parafollicular cells (C cells) in thyroid gland – Inhibits osteoclast activity; promotes Ca2+ loss by kidneys; decreases [blood Ca2+] Homeostatic control of calcium (and phosphate) levels in body fluids Calcium Calcium Dairy products ~70% of daily Ca Calcium Calcium Bioavailability Dairy products: 30% bioavailable Supplements: ~30% (depends on dose, form, if taken with meal) – Carbonate, citrate Poorly absorbed from “inhibitors”: – Phytic acid (raw beans, seeds, nuts, grains, soy isolates) – Oxalic acid (spinach, dried beans) Calcium RDAs take into account limited absorption of Ca2+ E.g., RDA of 1000mg assumes ~25-30% absorption Calcium Calcium Absorption Absorption increases with intake (e.g. lot’s of Ca in diet, absorption will increase to certain degree) Different preset absorptive efficiencies – Pregnancy/lactating: absorb more – Non-pregnant: ~30% absorbed; pregnant: ~50% If intake decreases, absorptive efficiency increases – BUT not enough to counter ongoing insufficient intake Calcium Factors Influencing Absorption Vitamin D status Calcium Factors Influencing Absorption Vitamin D status Intestinal transit time – Quick transit time --> less absorption Life cycle stage – breastfed infants absorb by passive diffusion – lose important stomach acids that help in breakdown as you age – loss of estrogen for postmenopausal women Calcium-Nutrient interactions Calcium Calcium Osteoporosis Calcium Deficiency (Osteoporosis) Skeletal disorder characterized by low bone strength predisposing a person to increased risk of fracture Osteoporosis Osteoporosis Osteoporosis Calcium Deficiency (Osteoporosis) Skeletal disorder characterized by low bone strength predisposing a person to increased risk of fracture 1/2 to 2/3 fractures in US attributed to low Ca2+ Diagnosing Osteoporosis: Densitometry Osteoporosis Measures how many grams of calcium and other bone minerals are packed into a segment of bone Osteoporosis Diagnosing Osteoporosis: Densitometry T-score >-2.5 – Differs from that of an average healthy 30 y old adults Z-score >-2 – Differs from that of someone your age, body mass, race, etc. Hip aBMD (g/cm2) Lumbar Spine aBMD (g/cm2) Wrist aBMD (g/cm2) 48 Osteoporosis Aging Chronic use of systemic glucocorticoids Female gender Secondary causes+ Fracture Risk Lifestyle factors* Rheumatoid arthritis Low BMI Low BMD Prior fracture Parental history of facture Osteoporosis Fracture Risk Osteoporosis Fracture risk assessment: FRAX Fracture prediction is enhanced when clinical risk factors are combined with BMD 10 year fracture risk Uses numerous risk factors associated with fracture http://www.shef.ac.uk/FRAX/ Osteoporosis Prevention of Osteoporosis Maximize development of peak bone mass during growth – Achieved btw 20-30 yrs – 60-80% genetic – 20-40% influenced by: Ca intake, activity, anorexia nervosa, substance abuse Strong musculature Minimize loss with age – Weight-bearing exercises – Maximize dietary Ca and vitamin D Calcium Calcium Supplementation Commonly recommended by physicians for adult women showing increased bone loss – Supplement in doses of 500mg or less Calcium carbonate: contains most elemental calcium by weight (40% vs. 21% in calcium citrate) Take with meals; don’t consume inhibitors at the same time – E.g. iron supplements, sodium Calcium Drink Milk? Summary: Calcium and Bone Health Hormonal control of blood calcium via PTH and calcitonin No blood test for Ca nutritional status (if deficient it is resorbed from skeleton to keep circulating levels normal – compromising bone health) Ca absorption declines with age Deficiency contributes to osteoporosis, and increases risk of fracture Calcium Excess Calcium Intake (hypercalcemia) Primarily from nutrient supplements Kidney Stones Hypercalcemia & renal insufficiency Symptoms: – Loss of muscle tone – Constipation – Large urine output – Nausea --> confusion --> coma --> death Calcium Phosphorus (P) Phosphorus nd 2 most abundant mineral in body 1% of body mass Phosphorus Many roles of phosphorus… Component of water soluble head of phospholipids (structure of cell membranes) Major constituent of genetic material (DNA, RNA) Essential for energy metabolism – High-energy bonds of ATP – Creatine phosphate Relaying signals to interior of cells (mediates hormone actions) Acts as a buffer (regulates pH in cytosol of all cells) Phosphorus Also … bone health! Hydroxy- and fluorapatite (along w/ calcium); provides rigidity to bones When blood phosphorus is low, active vitamin D is synthesized – Increases absorption of P and Ca from intestine – Increases release of P and Ca from bone When blood phosphorus is high, more lost from urine 80-85% is in bone The rest: cells, fluids outside cells (incl. blood) Phosphorus Remember? 63 Phosphorus Average intake of adults aged 18 to 74 yrs: Men = 1504 mg/day Women = 1124 mg/day Phosphorus Phosphorus Absorption Adults: 60-70% absorbed from typical diet – No evidence that absorption is affected by am’t in diet Location of absorption: small intestine Mechanisms: mostly passive diffusion; some active transport facilitated by vitamin D – Controlled by: vitamin D & phosphate transporters Blood levels loosely regulated & decline with age Phosphorus Deficiency Dietary deficiency unknown b/c recycled & widespread availability in foods However… – Some medications bind P and may lead to a deficiency – Alcoholism Symptoms: – Muscle weakness, anemia, bone pain, rickets (children), osteomalacia (adults), confusion Phosphorus Toxicity (hyperphosphatemia) UL: adults 19-80yrs 4 g/day Average intake of : Men = 1504 mg/day Women = 1124 mg/day Excess intake phosphorus may reduce Ca absorption (less problematic with adequate calcium intake) Concern re: high P intake b/c increased intake of colas/soft drinks – High intakes of polyphosphates may interfere with absorption of iron, copper, zinc Phosphorus Magnesium (Mg) Magnesium Many roles of magnesium … Enzyme cofactor (nucleotide synthesis, Na & K transport); involved in >300 enzymatic processes in cells Needed for metabolism of CHO, PRO, FAT – Used in glycolysis and energy generation Helps regulate BP (with Ca) Needed for activity of Na-K ATPase pump (active transport of Na and K across membranes) – Proper functioning of nerves, muscles (incl. heart) Important for DNA & RNA synthesis Magnesium Also … bone health! 50-60% of Mg in the body is in bone Essential for maintenance of bone structure Regulates Ca homeostasis Needed for action of vitamin D and many hormones, including PTH Magnesium Absorption Absorbed quickly; intestinal absorption inversely proportional to amount ingested – With average intake: ~50-60% absorbed – High intake: ~15-35% absorbed Controlled by: vitamin D & other hormones Bioavailability: ~50% – Inhibitors: high fibre, phosphate, or zinc intake Magnesium Magnesium Magnesium Deficiency Rare Associated with: – GI disorders – Malabsorption syndromes (Chron’s, Celiac) – Diabetes (excess urination) – Alcoholism Symptoms: – Nausea, muscle weakness & cramping, irritability, changes in BP & HR Toxicity UL: 350 mg/day from non-food sources over age 9 – Related to supplemental Mg intake ONLY Symptoms: – Diarrhea, hypotension, nausea, vomiting, flushing, cardiac complications, coma, death Magnesium Fluoride (F) Fluoride Functions: teeth and bones Not considered essential (not required for growth or to sustain life) BUT helps mineralize teeth and bones (95% located in calcified tissue [bones, teeth]) o Dental erosion can lead to tooth decay (dental caries); fluoride remineralizes tooth surface Children (10y); fluoride buildup in bones: join stiffness & bone pain Acute excess: nausea, vomiting, diarrhea, abdominal pain, excess salivation, convulsions, sensory disturbances (at 5 mg/kg body mass) Chronic excess: crippling skeletal fluorosis & osteoporosis What do you think? Should Regina fluoridate our water? How are Canadians Doing? (2004 CCHS-Nutrition) Health Canada considers prevalence of inadequate intake to be low when females) – Bone accrual fasted during growing years; important risk factor for fracture later in life Peak bone mass typically btw 20 and 30y Crash Course: Skeletal System Overview Summary: Calcium Adequate absorption depends on adequate levels of vitamin D; absorption varies with life stage (highest during pregnancy and infancy) Most is in bone – Deficiency can reduce bone mass and increase risk of osteoporosis – Toxicity: formation of kidney stones, interfere with absorption of other minerals Blood levels regulated by PTH (stimulates release Ca from bone, ↓ Ca excretion by kidney, activates Vit D) and calcitonin (blocks Ca release from bone) Other functions: essential for cell communication, nerve transmission, muscle contraction, blood clotting, BP regulation Summary: Phosphorus More widely distributed in diet than Ca Most found in bones & teeth 60-70% in typical diet is absorbed – Vitamin D aids in some absorption (active transport) Other functions: component of phospholipids, ATP, DNA, buffer that helps prevent changes in pH Summary: Magnesium ~50% in typical diet is absorbed – % absorbed ↓ as intake increases – active Vit D can enhance absorption Important for bone health & needed as cofactor for numerous reactions throughout body – Energy metabolism: enzyme activator and stabilizer for ATP – Maintains membrane potentials (essential for nerve and muscle conductivity) Summary: Fluoride Important for health of teeth and bones (protects against dental caries and can stimulate new bone formation) AI based on prevention of dental caries – Infants & children living in non-fluoridated water areas do not easily meet AI UL derived using data on risk of skeletal fluorsis END Bone Building Nutrients! Next: Review for Final Exam & Guest Lecture