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Week 9 - Bone Health.doc

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NUTR 1010
Andrea Buchholz

Week 9: Bone Health Bones -Bones are dynamic, living organs -Have many important roles in the body -Important to maintain healthy bones Functions of bones Structure and Support Metabolic Processes • Structural support for organs • Storage reservoir for and body segments minerals • Protects vital organs • Production of blood cells in bone marrow • Muscle support for movement Bone Structure -65% minerals Provides hardness (calcium and phosphorus) -35% organic substances Provide strength and flexibility (collagen: a fibrous protein) -Minerals form tiny crystals (hydroxyapatite), which cluster around collagen fibers Nutrients Involved in Bone Health -Major Roles: Calcium, vitamin D, and phosphorus -Minor Roles: Magnesium, vitamin K, vitamin A, and fluoride Bone Development Growth: -Determines bone size -Begins in womb -Continues until early childhood Modeling: -Determines bone shape -Longitudinal growth -Continues until early adulthood Remodeling: -Maintains bone integrity -Recycling -Bone resorption and formation -Adulthood Process of Bone Remodeling • Bone Resorption o Osteoclasts break down bone o Secretes enzymes and acids to erode bone surface o Minerals released into blood stream • Bone Formation o Formation of bone by osteoblasts o Build collagen matrix Peak Bone Mass -Highest amount attained during the years of normal bone growth rd -Achieved by the 3 decade of life -Important for osteoporosis prevention Influenced by: -Genetics -Nutrition -Physical Activity -Disease -Drugs Assessing Bone Health • Dual energy x-ray absorptiometry o Measures bone mineral density (BMD) o Bone mineral content (g)/bone area (cm2) = BMD (g/cm2) o Monitors changes in BMD o Determines risk of osteoporosis o Comparison of BMD values o T-score BMD Values in Adults Compares your BMD to average peak BMD of a 30-year-old healthy adult of similar gender and race. Osteopenia Osteoporosis -Most prevalent bone disease in North America -Low bone mass and deterioration of bone tissue -Bone is porous and thinner compared to a healthy individual -Bone is weak = decreased ability to bear weight -Increased bone fragility -Increased fracture risk Risk Factors of Osteoporosis -Modifiable: nutrient deficiencies, sedentary lifestyles, smoking, low body weight, alcohol abuse, repeated falls, hormone deficiencies, medications -Non-Modifiable: age, gender, ethnicity, fracture history, and family history Age as a Risk Factor • Risk increases as we age o BMD decreases gradually with age o Imbalance in bone remodeling o Resorption occurs ore rapidly than formation Gender as a risk factor • Women higher risk than men o Lower peak bone mass o Longer life expectancy o Hormonal changes o Estrogen promotes bone formation o Low estrogen levels, as occurs during menopause, causes increased bone resorption and decreases bone formation Calcium -Most abundant mineral in our body (makes up 2% of our body weight) -99% of Ca in our body found in bones and teeth (part of the structure of bones (hydroxyapatite crystals), providing strength and rigidity -Ca Bank, helping maintain blood Ca levels What about the other 1% of Ca in our body? • This 1% acts as an electrolyte; it is the active form of calcium (found in blood, soft tissues) • What does this mean? o Helps transmit nerve impulses o Helps muscles contract (contraction occurs when Ca flows into muscle cells) o Initiates blood clotting o Helps maintain healthy blood pressure o Our body controls blood Ca VERY TIGHTLY Normal blood Ca: 2.20-2.58 mmol/L • If blood Ca exceeds 2.58: o Hypercalcemia: loss of appetite, nausea, fatigue, muscle weakness, restlessness, confusion, Ca deposit in soft tissues • To avoid high blood levels, Ca is: o Deposited from blood into bones o Excreted by kidneys (more Ca lost in urine) o Decreased absorption from GI tract • The end result is a decrease in blood Ca back to normal With an adequate intake of calcium-rich food, blood calcium remains normal. With a dietary deficiency, blood calcium still remains normal. BECAUSE: Ca is released from bones Take away message: Blood calcium levels stay the same regardless of intake. How much Ca should we consume? -RDA for 19 to 50 year old adults is 1000 mg/d How much Ca are Canadians actually consuming? -Women: 793 mg/d -Men: 931 mg/d Sources of Calcium -Milk and milk products -Milk Alternatives and fortified foods (e.g., calcium fortified orange juice, soy milk) -Fish eaten with bones -Tofu (set in calcium) -Some nuts (almonds) and seeds (sesame) -Dark green veggies (kale, bok choy, broccoli) Bioavailability -The degree to which our bodies can absorb and use any given nutrient -Bioavailability of Ca is ~30% for many adults o I.e., most of us absorb and use ~30% of the Ca we consume o But, this value changes because: -Age: e.g., infants, children can absorb >60% of Ca -Requirements: e.g., pregnant women can absorb ~50% of Ca -Dietary factors: Phytates (e.g., in whole grains), oxalates (e.g., in spinach), tannins (in tea) decrease Ca absorption -How much we consume: i.e., when diet is high in Ca, absorption decreases; when diet is poor in Ca, absorption increases -Source of Ca Best source of calcium = Kale You need 3 cups of cooked broccoli (6 servings) to get as much calcium as 1 cup of milk Getting the most out of the Ca in your diet • Spread Ca intake throughout the day o Our bodies can absorb only so much Ca in one sitting • Phytates, oxylates, and tannins decrease absorption • Avoid taking zinc, iron, or magnesium supplements when eating a source of Ca o Competition for absorption Note for vegans and other dairy-free people • Good dairy-free sources o Milk alternatives (soy, rice, or almond milk) o High calcium leafy greens (kale, bok choy) o Tofu (set in calcium) o Almonds • Choose several of these foods daily What happens if we consume too much Ca? • E
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