© 2011 pearson education, inc. 11 nutrients involved in bone health

© 2011 Pearson Education, Inc.

11Nutrients Involved

in Bone Health


Bones

• Bones are living organs that contain • Bone tissue• Nerves• Cartilage• Connective tissue

• Blood vessels supply nutrients to bone to support its activities


Bones

• Bone provides strength and flexibility• Contains about 65% minerals, providing the

hardness of bone• Contains 35% organic structures for strength,

durability, and flexibility• Collagen: fibrous protein in bone tissue• Hydroxyapatite: mineral crystals around collagen

designed to bear weight


Bone Tissues

• Cortical bone (compact bone) 80% of the skeleton Outer surface of bone

• Trabecular bone (spongy bone) 20% of the skeleton Inside of bones (scaffolding) Supports outer cortical bone Faster turnover rate (sensitive to hormonal

changes and nutritional deficiencies)


Bone Development

• Bone growth: increase in bone size• Complete by age 14 in girls; age 17 in boys

• Bone modeling: shaping of bone• Complete by early adulthood

• Exercise and overweight increase thickness • Bone remodeling: recycling of bone tissue


Bone Development

• Bone density: compactness of bones• Peak bone density: when bones are

strongest• Factors associated with a lower peak bone

density: • Late pubertal age in boys• Late onset of menstruation in girls• Inadequate calcium intake• Low body weight• Physical inactivity during the pubertal years


Bone Remodeling

• Resorption: surface of bones is broken down by osteoclasts (cells that erode the surface of bones)

• New bone matrix formed by osteoblasts (bone builders)• Synthesize new bone matrix by laying down

collagen-containing component of bone


Bone Remodeling

• Bone resorption and formation are equal in young, healthy adults

• Resorption exceeds new bone formation after age 40: density begins to decrease

• High peak bone mass through proper nutrition and exercise: stronger skeleton • Protective against osteoporosis


Bone Health

• Dual energy x-ray absorptiometry (DXA)• Measures bone density • Results are compared with average peak bone

density of 30-year-old healthy adult• T-score is used to assess a person’s risk for

fracture and diagnose osteoporosis• Recommended for postmenopausal women


Nutrients for Bone Health

• Calcium is the most recognized nutrient associated with bone health

• Also essential for bone health: • Vitamins D and K• Phosphorus• Magnesium• Fluoride


Calcium

• Calcium absorption • Is enhanced in an acid environment• Requires 1,25-dihydroxyvitamin D

Calcium Metabolism


Functions of Calcium

• Provides structure for bones and teeth• Assists with acid−base balance• Transmission of nerve impulses• Assists in muscle contraction• Maintains healthy blood pressure• Initiates blood clotting• Regulates hormones and enzymes


Calcium Intake

• Adequate Intake (AI) varies with age and gender: 1,000 mg to 1,300 mg/day

• Upper Limit (UL): 2,500 mg• Bioavailability: body’s ability to absorb and

utilize calcium depends on• Individual’s age and calcium need • Dietary calcium and vitamin D• Binding factors (phytates, oxalates) in foods


Sources of Calcium

• Excellent sources include milk products • Skim milk, low-fat cheese, nonfat yogurt

• Other good sources include • Green leafy vegetables (kale, collard greens,

broccoli, and cabbage are low in oxalates)• Fortified foods (orange juice, soy milk)• Fish with edible bones (sardines, salmon)


Excess Dietary Calcium

• Excess dietary calcium is excreted in feces• Mineral imbalances from supplements• Hypercalcemia (high blood calcium)• Cause: cancer or parathyroid hormone (PTH)

overproduction• Symptoms: fatigue, appetite loss, constipation,

mental confusion, calcium deposits in soft tissues


Calcium Deficiency

• Osteoporosis from long-term calcium deficiency

• Hypocalcemia (low blood calcium) • Causes: kidney disease, vitamin D deficiency, or

diseases that inhibit the production of PTH • Symptoms: muscle spasms and convulsions


Vitamin D

• Fat-soluble vitamin• Excess is stored in liver, adipose tissue• Can be synthesized by the body from

exposure to UV rays from the sun• Considered a hormone: synthesized in one

location and regulates activities in other parts of the body


Functions of Vitamin D

• Regulates blood calcium levels (regulates calcium and phosphorus absorption from the small intestine)

• Stimulates osteoclasts when calcium is needed elsewhere in the body

• Required for bone calcification

Activation of Vitamin D


Vitamin D Adequacy

• AI: assume sun exposure is inadequate• Inadequate sun in the winter (latitude of more

than 40°N or more than 40°S)• Darker skin (more melanin pigment) reduces

the penetration of sunlight• People >65 years: decreased capacity to

synthesize vitamin D from the sun • Obesity: lower circulating vitamin D levels


Vitamin D Adequacy

• AI: 5 to 15 µg/day depending on age• UL: 50 µg/day for all age groups • Controversy: recent evidence suggests that

the current AI is not sufficient to maintain optimal bone health and reduce the risks for diseases such as cancer


Sources of Vitamin D

• Ergocalciferol (D2)—plants, supplements

• Cholecalciferol (D3)—animal foods, sun

• Most foods naturally contain little vitamin D• Mostly obtained from fortified foods (e.g., milk)• High amounts: cod liver oil, fatty fish (salmon,

mackerel, and sardines)• Vegetarians not consuming milk products receive

vitamin D from the sun, fortified soy or cereal products, or supplements


Vitamin D

• What happens if you consume too much?• Results in hypercalcemia

• What if you don’t consume enough?• Loss of bone mass: from fat malabsorption• Rickets (children), osteomalacia (adults)• Medications alter vitamin D metabolism and

activity: glucocorticoids, phenobarbital


Vitamin K

• Fat-soluble vitamin stored in the liver• Phylloquinone—plant form of vitamin K• Menaquinone—animal form of vitamin K

produced by bacteria in the large intestine• Functions of vitamin K• Blood coagulation• Bone metabolism


Vitamin K

• “Gla” protein production• Osteocalcin: secreted by osteoblasts (bone

remodeling)• Matrix Gla protein: in protein matrix of bone,

cartilage, blood vessel walls, soft tissues


Vitamin K

• Recommended intake• AI values are 120 µg/day for men and 90 µg/day

for women

• Sources of vitamin K• Synthesized by bacteria in the large intestine• Green leafy vegetables, vegetable oils


Vitamin K

• What if you consume too much?• No known side effects from large quantities

• What if you don’t consume enough?• Reduced blood clotting, excessive bleeding• Fat malabsorption (celiac disease, Crohn’s

disease, and cystic fibrosis) • Long-term use of antibiotics can lead to deficiency• Injection of vitamin K at birth for newborns


Phosphorus

• Phosphorus (as phosphate) is the major intracellular negatively charged electrolyte

• Functions of phosphorus• Critical in bone formation• Required for proper fluid balance• Component of ATP, DNA, membranes


Sources of Phosphorus

• High in protein-containing foods such as milk, meats, eggs

• In processed foods as a food additive: smoothness, binding, and moisture retention

• In soft drinks as phosphoric acid (milk-displacement effect)


Phosphorus

• What if you consume too much?• Excessive vitamin D supplements or phosphorus-

containing antacids can cause high phosphorus levels (muscle spasms and convulsions)

• What if you don’t consume enough?• Deficiencies are rare in healthy adults• Can occur in alcohol abuse, premature infants,

and elderly people with poor diets


Magnesium

• Kidneys regulate blood magnesium levels• Functions of magnesium• Mineral found in bone structure• Cofactor for over 300 enzyme systems• Required for ATP, DNA, and proteins• Supports vitamin D metabolism, muscle

contraction, and blood clotting


Magnesium

• Recommended intake• RDA varies based on age and gender• UL (pharmacological): 350 mg/day

• Sources of magnesium• Green leafy vegetables, whole grains, seeds,

nuts, seafood, beans, some dairy products• Dietary protein enhances absorption and retention


Magnesium

• What if you consume too much?• Excess supplements cause diarrhea, nausea,

cramps, dehydration, acid–base imbalances• Hypermagnesemia occurs in individuals with

impaired kidney function (antacid)

• What if you don’t consume enough?• Hypomagnesemia: results in hypocalcemia;

associated with osteoporosis, heart disease, high blood pressure, type 2 diabetes


Fluoride

• Trace mineral• Stored in teeth and bones• Functions of fluoride• Develop and maintain teeth and bones• Combines with calcium and phosphorus to protect

teeth from bacteria


Fluoride

• Recommended intake• AI varies by gender and increases with age,

ranging from 1 to 4 mg/day

• Sources of fluoride• Fluoridated dental products• Fluoridated water (not in bottled water)


Fluoride

• What if you consume too much fluoride?• Fluorosis (excess fluoride) increases the protein

content of tooth enamel and makes teeth porous; teeth become stained and pitted

• What if you don’t consume enough?• Dental caries (cavities)


Osteoporosis

• A disease characterized by• Low bone mass• Deterioration of bone tissue• Fragile bones leading to bone-fracture risk• Compaction of bone: decreased height• Shortening and hunching of the spine: kyphosis

(dowager’s hump)


Osteoporosis

• Risk factors for osteoporosis include:• Age • Gender• Smoking• Poor nutrition• Physical inactivity


Age

• Bone mass decreases with age• Age-related hormonal (estrogen and

testosterone) changes influence bone density• Decreased vitamin D metabolism with age


Gender

• 80% of Americans with osteoporosis: women• Women have lower bone density than men• Low estrogen production increases bone loss:

postmenopausal women and adolescent girls (extreme dieting)

• At risk: Caucasian women of low body weight with first-degree relative (mother or sister) with osteoporosis


Smoking and Poor Nutrition

• Cigarette smoking effects hormones that influence bone formation and resorption

• Alcoholism is associated with fractures• Caffeine increases urinary calcium loss• Dietary protein and calcium interaction• Low calcium and vitamin D intakes result in

low bone density


Physical Inactivity

• Regular exercise stresses bone tissues, stimulates bone density

• Weight-bearing activities (walking, jogging) are helpful in increasing bone mass


Female Athlete Triad

• Low energy availability (with or without eating disorders)

• Amenorrhea: hormonal changes (estrogen reduction) result in loss of menstruation

• Osteoporosis


Treatment for Osteoporosis

• There is no cure for osteoporosis• These slow the progression of osteoporosis:• Adequate calcium and vitamin D intake• Regular exercise (weight-bearing)• Anti-resorptive medications

© 2011 pearson education, inc. 11 nutrients involved in bone health

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