Bone Structure
- Provides strength to support the body
- allows for flexibility
- contains about 65% minerals - calcium & phosphorus, providing the hardness of the bone
- contains 35% organic structures for strength durability and flexibility
Collagen
Fiberous protein in bone tissue and connective tissue
Cortical bone (compact bone)
Very dense tissue making up 80% of the skeleton
- outer surface of all bones
- many of the small bones (wrists, hands, feet)
Trabecular bone (spongy bone)
Scaffolding" on the inside of bones; supports cortical bone and makes up 20% of the skeleton
- faster turnover rate than cortical bone
- accounts for higher rate of age-related fractures
Bones develop through 3 processes
1. Bone growth - increase in bone size; most completed by age 14 in girls and age 17 in boys
2. Bone Modeling - shaping of the bone; completed by early adulthood
3. Bone Remodeling - reshaping of bone; occurs throughout life
Remodeling - bone recycling
Involves 2 steps
- resorption: surface of bones is broken down
- osteoclasts - cells that secrete enzymes and acids to erode the surface of bones
- formation of new bone by cells called osteoblasts
Osteoblasts
Bone building cells that produce the collagen- containing component of bone, The hydroxyapetite crystallizes and packs together to create new bone where needed
Bone Density
- Peak bone density is reached before age of 30
- In young health adults, the processes of bone resorption and formation are equal, so that just as much bone is broken down as is built, maintaining bone mass
- Density begins to decrease after age 40 becau
Dual-energy x-ray absorptiometry (DXA or DEXA)
- Most accurate tool for measuring bone density
- Uses very-low level x-ray energy
- Provides full body scan or can be used to scan peripheral regions (wrist, heel)
- Simple, painless and non invasive procedure
- Recommended for post menopausal women
- A
Calcium
- Most abundant major mineral in the body
- 99% of body calcium is found in bone
- 2% of our entire body weight
Functions of calcium
- forms and maintains bones and teeth
- assists with acid-base balance
- transmission of nerve impulses
- assists in muscle contraction
Low calcium level
- parathyroid glands produce parathyroid hormone (PTH)
- PTH stimulates activation of vitamin D
- PTH and vitamin D cause: kidneys to reabsorb more calcium from the blood, osteoclasts to break down bone and release calcium, stimulation of calcium absorpti
High calcium level
- Thyroid gland releases calcitonin
- Calcitonin functions to inhibit the actions of vitamin D
- prevent calcium reabsorption from kidneys
- limit calcium absorption from intestines
- inhibit osteoclasts from breaking down bone
Recommended Intake: Calcium
- RDA values for Calcium vary with age and gender from 1,000mg to 1,200mg/day in adults
Sources of Calcium
- Skim milk, low-fat cheese, nonfat yogurt, green leafy vegetables - kale, collard greens, turnip greens, broccoli, brussel sprouts and bok choy.
Bioavailability
- Degree to which a nutrient is absorbed and used
Calcium Bioavailability depends on need and age
- infants & children can absorb over 60%
- Pregnant & lactating women can absorb 50%
- healthy adults typically absorb 30%
- older adults absorb less and can be as low as 25%
- appears that max. absorbed at one time is limited to 500mg
- numerous factors
Consume too much calcium?
- excess calcium is excreted from the body
- calcium supplements can lead to mineral imbalances, iron, zinc, and magnesium
- Hypercalcemia ( high blood calcium) can be caused by cancer and over production of PTH
- Kidney stones are associated with high in
Not enough calcium?
- Hypocalcemia (low blood calcium) can be caused by kidney disease or vitamin D deficiency
Vitamin D
- Fat-soluble vitamin
- excess stored in liver and adipose tissue
- can be synthesized by the body by exposure to UV light or obtained from our diet
- Is a hormone because it is synthesized in one location and acts in another location
Functions of Vitamin D
- Required for calcium and phosphorus absorption
- regulates blood calcium levels
- works with PTH to stimulate osteoclasts
- necessary for calcification of bone
- may play a role in cell differentiation
Recommended Intake: Vitamin D
- DRI is 600 UI/day for children and most adults
- Upper level intake for most adults is 4000 IU/day
- If your exposure to sun is adequate then you do not need to consume vitamin D in your diet
- Northern latitudes receive inadequate sunlight in the winte
Factors influencing vitamin D synthesis
- Vitamin D synthesized when suns rays are strongest between 9AM and 3PM
- Melanin pigment reduces the penetration of sunlight
- People > 65 years old experience a fourfold decrease in their capacity to synthesize vitamin D due to reduced skin thickness
-
Sources of Vitamin D
- most foods naturally contain very little Vitamin D
- D2 ergocalciferol found in plant foods
- D3 cholecalciferol found in animal foods
- Fatty fish best sources - sardines, salmon, herring
- Most Vitamin D is obtained from fortified foods such as milk a
Too much Vitamin D?
- Occurs from vitamin supplements, not from excessive exposure to sunlight
- results in hypercalcemia - high blood calcium
Not enough vitamin D?
- occurs with disease that reduce intestinal absorption of fat and limited exposure to sunlight
- Rickets - occurs in children; inadequate mineralization of bones
- Osteomalacia - Vitamin D deficiency in adults, bone become weak and prone to fractures
Vitamin K
- Fat-soluble vitamin
- Stored primarily in liver
- Phylloquinone - plant form of vitamin K
- menaquinone - form of vitamin K produced by bacteria in the large intestine
Functions of Vitamin K
- Blood coagulation (prothrombin synthesis)
- Bone metabolism ( osteocalcin synthesis)
Recommended Intake: Vitamin K
- no RDA for vitamin K
- AI values are 120 mg/day for men and 90 mg/day for women
Sources of Vitamin K
- Only a few foods contribute to our dietary intake of vitamin K, green leafy veges-kale, spinach, collard greens, turnip greens, lettuce and vege oils
Too much Vitamin K?
- no side effects from large quantities
Not enough Vitamin K?
- Reduced blood clotting, excessive bleeding
- Occurs with diseases that limit absorption of fat in the small intestine - celiac disease, crohns disease and cystic fiberosis
- Newborns are given an injection at birth because they lack the intestinal bacte
Phosphorus
- Phosphorus (as phosphate) is the primary intracellular negatively charged electrolyte
Function of Phosphorus
- critical to mineral composition of bone about 85% of our body's phosphorus is stored in our bones
- required for proper fluid balance
- activates and deactivates enzymes
- component of ATP, DNA, lipoproteins and cell membranes
Recommended Intake: Phosphorus
- RDA for phosphorus 700mg/day
Sources of phosphorus
- high in protein-containing foods such as milk, meals and eggs
- in processed foods as a food additive
- in soft drinks as phosphoric acid for a tart flavor and to slow the growth of molds and bacteria
Too much phosphorus?
- People with kidney disease or consumption of too many phosphorus-containing antacids can cause elevated phosphorus levels, muscle spasms and convulsions
Not enough phosphorus?
- Deficiencies are rare in health adults
- malnutrition, parathyroidectomy and those who overuse calcium antacids may have low blood P levels
Magnesium
- The bones contain 50-60% of body's magnesium
- Our total body magnesium content is 25gms
Functions of Mg
- A mineral found in bone structure - formation of hydxyapatetite crystals
- Cofactor for over 300 enzyme systems
- required for the production and repair of ATP, DNA and proteins
- May improve insulin sensitivity and decrease the risk of colorectal cance
Recommended intake: Mg
- RDA varies bases on age and gender
- 310mg/day women age 19-30
- 400mg/day men age 19-30
Sources of Mg
- Green leafy veges, whole grains, seeds, nuts, seafood, beans, some dairy
- people who are adequately nourished generally consume plenty of Mg in their diet
Too much Mg?
- no toxicity from Mg in food
- Mg supplements can cause diarrhea, nausea, cramps, dehydration and cardiac arrest
Not enough Mg?
- Hypomagnesmia may develop from chronic diarrhea, kidney disease or chronic alcohol abuse
- Associated with osteoperosis, heart disease, high BP, type 2 diabetes
- Other symptoms - muscle cramps, spasms, nausea, weakness and confusion
Fluoride
- Fluoride is a trace mineral
- 99% of body's fluoride is stored in teeth and bones
Functions of Fluoride
- development and maintenance of teeth and bones
- combines with calcium and phosphorus to make fluorohydroxyaptitate which makes tooth enamel stronger, protecting teeth from cavities
- Inhabits the metabolism of acid producing bacteria that cause tooth d
Recommended Intake: fluoride
- RDA varies by gender & increases with age ranging from 1-4 mg/day
Sources of Fluoride
- Fluoridated water and dental products
- No reliable evidence that fluoride increases our risk of cancer, bone fractures, infertility or Alzheimer's
- Toothpastes and mouthwashes can contribute to as much or more fluoride to our diets than fluoridated wa
Too much Fluoride?
- Fluorsis (excess fluoride) creates porous tooth enamel, teeth become stained and pitted
- mild fluorsis causes white patches on teeth
- children should not swallow toothpaste or mouthwash
Not enough Fluoride?
- dental caries (cavities)
- possible lower bone density
In depth: Osteoporosis
Osteoporosis is a disease charactericized by:
- low bone mass
- deterioration of bone tissue
- more than 2 million fractures each year are attributed to osteoporosis
- Osteoporosis of the spine from gradual compression fractures in the vertebrae
- shorten
Factors influencing the risk of osteoporosis
- Age
- Gender
- genetics
- Consumption of tobacco, alcohol, caffeine
- Nutrition
- Physical activity
- History of amenorrhea
Age is a factor because
- bone mass decreases with age
- age-related hormonal changes influence bone density (reduced estrogen and testosterone production)
- Older adults are less able to absorb Vitamin D
Gender is a risk factor because
- 80% of Americans with osteoporosis are women
- women have lower absolute bone density than men
- Estrogen loss in post menopausal women causes increased bone loss
- Women live longer than men, and because risk increases with age, more elderly women suff
Physical activity influences the risk for osteoporosis
- regular exercise is highly protective against bone loss and osteoporosis
- exercise causes our muscles to contract, stressing bones that stimulates increased bone loss
- weight bearing activities ( walking, jogging) especially helpful in increasing bone
Treatment for osteoporosis
- No cure
Progression of osteoporosis may be slowed by:
- adequate calcium and vitamin D intake
- regular exercise
- antiresorptive medications
- hormone replacement therapy