Transcript 11. Nutrients Involved in Bone Health

Chapter 11 Lecture
Chapter 11:
Nutrients
Involved in Bone
Health
© 2017 Pearson Education, Inc.
Bones
• Bones are living organs that contain
• Bone tissue
• Cartilage
• Connective tissue
• Nerves and blood run within channels in bone to
support its activities
© 2017 Pearson Education, Inc.
Bones (cont.)
• Bone provides strength and flexibility
• Contains about 65% minerals, providing the
hardness of bone
• Contains 35% organic structures for strength,
durability, and flexibility (collagen)
• Hydroxyapatite: mineral crystals around
collagen designed to bear weight
© 2017 Pearson Education, Inc.
© 2017 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)
© 2017 Pearson Education, Inc.
© 2017 Pearson Education, Inc.
Bone Development
• Bone growth: increase in bone size
• Complete by age 18 in girls; age 21 in boys
• Bone modeling: shaping of bone
• Complete by early adulthood
• Exercise and overweight increase thickness
• Bone remodeling: recycling of bone tissue
© 2017 Pearson Education, Inc.
© 2017 Pearson Education, Inc.
Bone Development (cont.)
• 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
© 2017 Pearson Education, Inc.
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
builder cells)
• Synthesize new bone matrix by laying down
collagen-containing component of bone
© 2017 Pearson Education, Inc.
Bone Remodeling (cont.)
• 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
© 2017 Pearson Education, Inc.
© 2017 Pearson Education, Inc.
Assessing Bone Health
• Dual energy x-ray absorptiometry (DXA or
DEXA)
• Non-invasive measurement of 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
© 2017 Pearson Education, Inc.
© 2017 Pearson Education, Inc.
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
© 2017 Pearson Education, Inc.
Calcium
• Calcium absorption
• Is enhanced in an acid environment
• Requires 1,25-dihydroxyvitamin D
© 2017 Pearson Education, Inc.
Functions of Calcium
•
•
•
•
•
•
•
Provides structure for bones and teeth
Assists with acid−base balance
Assists in transmission of nerve impulses
Assists in muscle contraction
Maintains healthy blood pressure
Initiates blood clotting
Regulates hormones and enzymes
© 2017 Pearson Education, Inc.
© 2017 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
© 2017 Pearson Education, Inc.
© 2017 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)
© 2017 Pearson Education, Inc.
© 2017 Pearson Education, Inc.
© 2017 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
© 2017 Pearson Education, Inc.
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
© 2017 Pearson Education, Inc.
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
© 2017 Pearson Education, Inc.
© 2017 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
• May decrease cancer growth
• Involved in cell differentiation
© 2017 Pearson Education, Inc.
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 have decreased capacity to
synthesize vitamin D from the sun
• Obesity causes lower circulating vitamin D levels
© 2017 Pearson Education, Inc.
© 2017 Pearson Education, Inc.
Vitamin D Intake Recommendations
• RDA: 600 IU for men/women ages 19 to 70; 800
IU for adults over age 70
• UL: 4,000 IU for everyone over 9 years of age
• Controversy: Recent evidence suggests that the
current RDA is not sufficient to maintain optimal
bone health and reduce the risks for diseases
such as cancer
© 2017 Pearson Education, Inc.
© 2017 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
© 2017 Pearson Education, Inc.
© 2017 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
© 2017 Pearson Education, Inc.
© 2017 Pearson Education, Inc.
Vitamin K
• Fat-soluble vitamin stored in the liver
• Phylloquinone: plant form (dietary) of vitamin K
• Menaquinone: animal form of vitamin K
produced by bacteria in the large intestine
• Vitamin K functions as coenzyme:
• Blood coagulation
• Bone metabolism
© 2017 Pearson Education, Inc.
© 2017 Pearson Education, Inc.
Vitamin K (cont.)
• "Gla" protein (bone protein) production
• Osteocalcin: secreted by osteoblasts (bone
remodeling)
• Matrix Gla protein: in protein matrix of bone,
cartilage, blood vessel walls, soft tissues.
May prevent calcification of arteries, reducing
risk of CVD
© 2017 Pearson Education, Inc.
Vitamin K (cont.)
• 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 (kale, spinach, collard
greens, lettuce)
© 2017 Pearson Education, Inc.
© 2017 Pearson Education, Inc.
Vitamin K (cont.)
• 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
© 2017 Pearson Education, Inc.
Phosphorus
• Phosphorus is the major intracellular negatively
charged electrolyte
• An essential component of all cells, found in
both plants and animals
• Functions of phosphorus
• Critical in bone formation
• Required for proper fluid balance
• Component of ATP, DNA, membranes
© 2017 Pearson Education, Inc.
Sources of Phosphorus
• High in protein-containing foods such as milk,
meats, eggs, legumes
• In processed foods as a food additive:
smoothness, binding, and moisture retention
• In soft drinks as phosphoric acid
• High phosphorus diet linked with premature
mortality in healthy adults
© 2017 Pearson Education, Inc.
Phosphorus (cont.)
• 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
© 2017 Pearson Education, Inc.
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
© 2017 Pearson Education, Inc.
Magnesium (cont.)
• 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
© 2017 Pearson Education, Inc.
© 2017 Pearson Education, Inc.
Magnesium (cont.)
• 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
© 2017 Pearson Education, Inc.
Fluoride
• Trace mineral, stored in teeth and bones
• Combines with calcium and phosphorus to form
fluorohydroxyapatite to form teeth
• Functions of fluoride
• Develop and maintain teeth and bones
• Combines with calcium and phosphorus to
protect teeth from bacteria
• Stimulates bone growth
© 2017 Pearson Education, Inc.
Fluoride (cont.)
• 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)
© 2017 Pearson Education, Inc.
Fluoride (cont.)
• 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)
© 2017 Pearson Education, Inc.
© 2017 Pearson Education, Inc.
Osteoporosis
• Most prevalent disorder affecting bone health
• Characterized by:
• Low bone mass
• Deterioration of bone tissue
• Fragile bones leading to bone-fracture risk
• Bone compaction: decreased height
• Shortening and hunching of the spine:
kyphosis (dowager's hump)
© 2017 Pearson Education, Inc.
• Osteoporitic vertebrae (left) and healthy
vertebrae (right).
© 2017 Pearson Education, Inc.
© 2017 Pearson Education, Inc.
Osteoporosis (cont.)
• Risk factors include:
• Age
• Gender
• Tobacco, alcohol, and caffeine
• Poor nutrition
• Physical inactivity
© 2017 Pearson Education, Inc.
© 2017 Pearson Education, Inc.
Osteoporosis Risk: Age
• Bone mass decreases with age
• Age-related hormonal (estrogen and
testosterone) changes influence bone density
• Decreased vitamin D metabolism with age
© 2017 Pearson Education, Inc.
Osteoporosis Risk: Gender And Genetics
• 80% of Americans with osteoporosis are women
• Women have lower bone density than men
• Low estrogen production increases bone loss:
postmenopausal women and adolescent girls
(extreme dieting)
• Caucasian women of low body weight with firstdegree relative (mother or sister) with
osteoporosis at greater risk
© 2017 Pearson Education, Inc.
Osteoporosis Risks: Smoking/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
© 2017 Pearson Education, Inc.
Osteoporosis Risk: Physical Inactivity
• Regular exercise postively stresses bone
tissues, stimulates bone density
• Weight-bearing activities (walking, jogging) can
help increase bone mass
© 2017 Pearson Education, Inc.
Nutrition and Osteoporosis
• Fruit and vegetable consumption associated with
improved bone health
• Good sources of vitamins C and K, as well as
magnesium
• Protein: effect on bone health is controversial
• High intake may increase calcium loss
• Low protein intake also associated with bone risks
• Calcium & vitamin D are important throughout the life
span
• Sodium: high intakes appear to have a negative impact,
but studies are inconclusive
© 2017 Pearson Education, Inc.
Treatment for Osteoporosis
• There is no cure for osteoporosis
• Factors that slow the progression of
osteoporosis:
• Adequate calcium and vitamin D intake
• Regular (weight-bearing) exercise
• Resistance training
• Certain medications (may have side effects)
© 2017 Pearson Education, Inc.