Download Bones

11
Nutrients Involved
in Bone Health
© 2011 Pearson Education, Inc.
Bones
• Bones are living organs that contain
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Bone tissue
Nerves
Cartilage
Connective tissue
• Blood vessels supply nutrients to bone to
support its activities
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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
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
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)
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
Bone Development
• Bone density: compactness of bones
• Peak bone density: when bones are
strongest
• Factors associated with a lower peak bone
density:
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Late pubertal age in boys
Late onset of menstruation in girls
Inadequate calcium intake
Low body weight
Physical inactivity during the pubertal years
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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
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
Nutrients for Bone Health
• Calcium is the most recognized nutrient
associated with bone health
• Also essential for bone health:
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Vitamins D and K
Phosphorus
Magnesium
Fluoride
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Calcium
• Calcium absorption
• Is enhanced in an acid environment
• Requires 1,25-dihydroxyvitamin D
Calcium Metabolism
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Functions of Calcium
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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
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
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)
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
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
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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
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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
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
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
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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
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
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
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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
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
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
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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 (milkdisplacement effect)
© 2011 Pearson Education, Inc.
Phosphorus
• What if you consume too much?
• Excessive vitamin D supplements or phosphoruscontaining 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
© 2011 Pearson Education, Inc.
Magnesium
• Kidneys regulate blood magnesium levels
• Functions of magnesium
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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
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
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)
© 2011 Pearson Education, Inc.
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)
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
Osteoporosis
• A disease characterized by
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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)
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
Osteoporosis
• Risk factors for osteoporosis include:
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Age
Gender
Smoking
Poor nutrition
Physical inactivity
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
Age
• Bone mass decreases with age
• Age-related hormonal (estrogen and
testosterone) changes influence bone density
• Decreased vitamin D metabolism with age
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
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
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Physical Inactivity
• Regular exercise stresses bone tissues,
stimulates bone density
• Weight-bearing activities (walking, jogging)
are helpful in increasing bone mass
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Female Athlete Triad
• Low energy availability (with or without eating
disorders)
• Amenorrhea: hormonal changes (estrogen
reduction) result in loss of menstruation
• Osteoporosis
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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.