Chapter 11 Nutrients Involved in Bone Health The Composition of Bone Provides Strength and Flexibility Bones need to be both strong and flexible o 65 of bone tissue is made of minerals that provides hardness o 35 is a mixture of organic substances that provide strength durability and flexibility Collagen fibrous protein Hydroxyapatite tiny crystals that cluster around the collagen fibers o Enables bones to bear weight while responding to demands form movement Cortical bone compact bone is very dense o 80 of the skeleton o The outer surface of bones Trabecular bone o 20 of the skeleton o Inside and the ends of long bones o Spongy bone o Have a faster turnover rate than cortical bone Bone Growth and Modeling Determine the Size and Shape of our Bones Bone growth the size of bone increases o Most girls reach their adult height by 14 and boys 17 Bone modeling the process by which the shape of bones is determined o Can still increase in thickness if they are stressed by repetitive exercise such as weight training or by being overweight or obese Bone Remodeling Maintains a Balance Between Breakdown and Repair Bone density compactness of bones Peak bone density the point at which bones are strongest o Lower peak density include later pubertal age in boys and late onset of menstruation in girls inadequate calcium intake low body weight and physical inactivity during the pubertal years o Before 30 we have peaked bone mass Remodeling bone recycling Resorption bone is broken down Osteoclasts erode the bone surface Osteoblasts bone builders new bone is formed o Synthesize new bone matrix by laying down the collagen containing organic component of bone o In young healthy adults the processes of bone resorption and formation are equal o Around 40 bone resorption begins to occur more rapidly than bone formation Results in an overall loss in bone density o High peak bone mass through proper nutrition and exercise Stronger skeleton How Do We Assess Bone Health Dual energy x ray absorptiometry DEXA measures bone density o Compared to the average peak bone density of a 30 year old healthy adult o T score asses the risk of fracture and determine whether or not the person has osteoporosis o Recommended for post menopausal women A Profile of Nutrients That Maintain Bone Health Calcium Functions o Provide structure to the bones and teeth o Stored in the hydroxyapatite crystals o Alkaline basic Assisting with acid base balance o Can t survive for long if our blood calcium level rises above or falls below a very narrow range o Critical for the normal transmission of nerve impulses o Assists in muscle contraction Stimulated by calcium flowing into the muscle cell muscles relax when calcium is pumped back outside o Secretion of parathyroid hormone low blood calcium levels o Secretion of calcitonin high blood calcium levels o Maintenance of healthy blood pressure the initiation of blood clotting and the regulation of various hormones and enzymes o 19 50 years 1 000 mg o Over 50 1 200 mg o UL 2 500 mg o Bioavailability the degree to which the body can absorb and utilize any given nutrient Depends in part on a person s age and his or her need for calcium RDI o Dietary factors can also affect the absorption of calcium Binding factors such as phytates and oxalates Vitamin d Food sources o Skim milk low fat cheeses and non fat yogurt o Green leafy vegetables o Calcium fortified juices soymilk rice milk and tofu processed with calcium o Canned fish with bones Toxicity o Usually excreted in feces o Toxicity from supplements can lead to health problems Hypercalcemia blood calcium levels reach abnormally high concentrations Can be caused by cancer and by overproduction of pth Symptoms fatigue loss of appetite constipation and mental confusion coma and death Calcium deposits in the soft tissue Deficiency o No short term symptoms o Long term Hypocalcemia abnormally low level of calcium in the blood Cause kidney disease vitamin d deficiency and diseases that inhibit the production of pth Symptoms muscles spasms and convulsions Vitamin D Fat soluble excess amounts are stored in the liver and adipose tissue The body can synthesize using energy from exposure to sunlight Considered a hormone because it is made in one part of the body yet regulates various activities in other parts of the body Functions o Regulate blood calcium levels Regulates the absorption of calcium and phosphorus from the small intestine o Works with pth to stimulate osteoclasts to break down bone when calcium is needed elsewhere in the body o Calcification of the bone RDI o Synthesized during the time of day when the sun s rays are strongest o Darker skin reduces the penetration of sunlight o 65 decrease in their capacity to synthesize vitamin d from the sun o Obesity is associated with lower levels of circulation vitamin d o 19 50 5mg o 50 70 10 mg o 70 15 mg o UL 50 mg o Current research says that the current AI is not sufficient Food sources o Two forms of vitamin d Ergocalciferol Vitamin d 2 Plant foods May also be used in vitamin d supplements Cholecaciferol Vitamin D 3 Animal foods and synthesize from the sun o Fortified milk o Cod liver oil fatty fish and certain fortified cereals Toxicity Deficiency o Hypercalcemia o Loss of bone mass o Malabsportion of fat o In children rickets o In adults osteomalacia Vitamin K Fat soluble stored primarily in the liver Phylloquinone primary dietary form of vitamin k o Found in plants Menaquinone produced by bacteria in the large intestine o Animal form Functions o Coagulation of blood o Two bone proteins Gla proteins Osteocalcin Matrix gla protein Secreted by osteoblasts Located in the protein matrix of bone and is also found in cartilage blood vessel walls and other soft tissues RDI o 120 90 mg o No UL Food sources Toxicity o None Deficiency o Green leafy vegetables o Reduced ability to form blood clots leading to excessive bleeding o Rare in humans More likely for malabsorption of fat IE celiac disease crohn s disease and cystic firbrosis Long term use of antibiotics Newborns are usually given a shot of vitamin k at birth Phosphorus Major intracellular negatively charged electrolyte Functions o Critical role in bone formation o 85 stored in bones Food sources o Milk meats and eggs o Found in many processed foods as a food additive Smoothness binding and moisture retention Acid is added to soft drinks Toxicity Deficiency o Rare Magnesium o From vitamin d supplements or too many phosphorus containing anti
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