Week 13- Bone health

Types of Bones

• Cortical (compact): Very dense, provides strength on outer length of long bones and main

tissue of smaller bones

• Trabecular (spongy): Less dense, responds to changing hormone levels and more readily

releases minerals, greater turnover

Bones:

Bones are metabolically active – constantly broken down and rebuilt – blood vessels and nerves run through the cente

Composition of Bones

• 65% inorganic matter → mineral crystals deposited into collagen

• 35% organic matter → collagen (protein)

• The inorganic matter (minerals) provide the strength and structural support of

bones which keep us upright and provide protection to organs

• Organic material (collagen) allows flexibility to bones (needed for times of stress

or pressure. i.e., jumping

Bone mineral density:

Measure of how tightly mineral crystals are packed into the protein matrix, indicator of bone strength

• Ratio of bone mineral content relative to bone size

How to mesure bone density?

• Measured using dual energy x-ray absorptiometry (DEXA) and can estimate risk of or extent of

osteoporosis

osteoporosis

Brittle bones (crystal not as dense, lack of Ca)

Disease caused from excessive loss of bone resulting in porous and fragile bones →

results in increased risk of fractures and break

Bone Growth:

• Process of breaking down and rebuilding bones to increase in length and density

• Length: Stops typically around 14 years for girls, 17 years for boys

• Bone Density: Continues into young adulthood (into your 20s)

Osteoclasts:

Cells in the bone that break down bone during growth

Osteoblasts:

Cells in the bone that rebuild bone during growth (if we sustain them, we will lose our bones)

Bone Remodeling:

Reshaping of the bone, this process occurs throughout

adulthood to repair microdamage

• Over time, osteoclasts remain active, osteoblasts reduce in activity, resulting in

bone loss

Lifestyle Factors that Influence Bone Health

• Nutrition → adequate intake of vitamin D, calcium, and protein intake

• Weight bearing exercises → strengthens bones and decreases bone loss that occurs with age

• Alcohol intake

• Smoking

• Stress

• Sleep

• Body weight

Non-Lifestyle Factors…

• Genetics

• Age

Calcium

• Most abundant mineral in the body

• 1% found in body’s fluids, the rest (99%) is stored in bones (and teeth)

• In bones:

• Forms integral part of bone structure

alongside phosphorus

• Calcium stores → readily available for

body’s fluid when blood calcium drops

Calcium Function In Bones (99%):

Calcium salts form hydroxyapatite crystals (calcium phosphorus) in protein matrix (collagen)

• During mineralization these crystals become denser → strength and rigidity

• Bones are continuously gaining and losing mineral

Calcium Function in Body Fluids (1%)

• Maintain normal blood pressure → Acts in renin-angiotensin system

• Participates in blood clotting

• Binds to proteins to activate them to participate in muscle contractions, nerve impulses, secretion of hormones, activation of enzymatic reactions (e.g., Calmodulin activated by calcium and then breaks down glycogen for muscle contraction

Calcium Balance

• Depends on the: Thyroid and Parathyroid gland, Intestines, Bones, Kidneys

• Two hormones (Calcitonin & parathyroid hormone) and Vitamin

Low Blood Calcium

• Parathyroid gland secretes parathyroid hormone into blood

• Parathyroid hormone stimulates activation of Vitamin D

• In Kidneys: Parathyroid hormone and Vitamin D stimulate calcium

reabsorption into the blood

• In Intestines: Vitamin D enhances calcium absorption

• In Bones: Vitamin D and Parathyroid hormone stimulate osteoclast cells (breakdown)

to break down bone, releasing calcium into blood

• Blood calcium is then raised, and parathyroid secretion inhibite

High blood calcium

• Thyroid gland secretes calcitonin

• In Kidneys: Calcitonin inhibits Vitamin D activation and prevents

reabsorption of calcium

• Intestines: Calcitonin limits calcium absorption (from inhibiting Vitamin D

activation)

• Bones: Calcitonin inhibits osteoclast cells from breaking down bone and

releasing calcium

• Blood calcium is lowered and calcitonin secretion is inhibited.

Calcium Absorption

• Adults absorb approximately 30% of calcium digested

• Body will increase absorption when needed (times of growth, times of

inadequate intake)

• Enhancers: Stomach acid, Vitamin D, Lactose (in infants only)

• Partly why milk products are fortified with Vitamin D!

• Inhibitors: Vitamin D deficiency, lack of stomach acid, high phosphorus intake,

phytates (grains)* and oxalates (vegetables)* minor effect overa

Too much calcium in blood

calcium rigor

• Hardness or stiffness of muscles due to high blood calcium concentration,

muscles contract but cannot releas

Too little calcium in blood

calcium tetany

• Uncontrolled muscle contractions, spasms

***Not related to dietary deficiency or excess → caused by lack of vitamin D or

abnormal secretion of hormones

• Dietary deficiency from inadequate intake or malabsorption issues will result in

depletion of the bones, not the bloo

Calcium Recommendation (RDA, UL)

• Adults (19-50 yrs old): 1000mg/day

• Men (51-70 yrs old): 1000mg/day

• Men (>71 yrs old): 1200mg/day

• Women (>50 yrs old): 1200mg/day

• * Higher for children and adolescents

• UL: 2500mg/day (19-50 yrs old)

• UL: 2000mg/day (>50 yrs old

Calcium food sources

Milk products (milk, yogurt, cheese), fortified plant-based milk alternatives, sardines with

bones, tofu made with calcium salt, tahini, broccoli, cabbage

Calcium Deficiency:

• Inadequate intake during growth years – limits bones’ ability to reach peak mass

and density, stunted growth in children

• Bone loss in adults – Osteoporosis

• Blood calcium will remain high, although bones are becoming depleted and

losing density

Calcium Toxicity:

• From supplementation, not food

• Constipation

• Increased risk of kidney stones (collection of calcium in kidneys)

• Interference with absorption of other minerals (e.g., iron

Phosphorus

• Second most abundant mineral in human body

• 85% is combined with calcium to form the

hydroxyapatite crystals in bones and teeth

• Other 15% in soft tissue (muscle and kidneys)

• ***Many other roles***

Phosphorus recommendation and food sources:

• RDA: 700mg/day

• UL: 4000mg/day

• Food Sources: Protein-rich foods (animal protein, cottage cheese), milk, salmon, navy beans, also found in soft drinks/pop

Phosphorus deficiency and toxicity:

Deficiency:

• Very rare, muscular weakness and bone pain

Toxicity:

• Calcification of non-skeletal tissues, particularly kidneys

• Increased Ca++ excretion from bones (*Overabundance of phosphorus and

inadequate intake of calcium in diet is detrimental to bones and teeth

Vitamin D

• Body can synthesize Vitamin D with the help of sunlight (precursor body makes from

cholesterol)

• Sunlight rays strike the precursor in skin → 7-dehydrocholesterol

• 7-DC transformed to inactive Vitamin D3 precursor which is absorbed directly

into blood

• Liver & kidney convert precursor to active 1, 25 hydroxyvitamin D3 (calcitriol)

***Diseases of the liver and kidney can result in vitamin D deficiency

• Active form of vitamin D in the body is a hormone (travels from one part of the body

to another and triggers a response in the body)

• Similar to Vitamin A – Vitamin D also has a binding protein needed to be carried to

organs (Vitamin D Binding Protein – DBP)

Vitamin D Function

• Bone Growth: Assists in absorption of calcium and phosphorus to maintain

blood concentrations, impacting health of bones and teeth

• Raises blood concentrations of bone minerals in three ways:

• 1. Vitamin D enhances absorption of needed minerals (calcium and

phosphorus) from GI tract when diet is sufficient

• 2. When diet is insufficient, reabsorption of minerals in kidneys (with

parathyroid hormone)

• 3. Mobilization of minerals from bones to blood (stimulation of osteoclasts)

• Other roles: Connected to immune system, brain and nervous system,

pancreas, skin, muscles, cartilage, and reproductive organs

→its function on disease prevention is still uncertai

Vitamin D Significant Sources and RDA and UL:

Recommendation (RDA, UL) (dont need to know)

• Adults (19-70 years): 600 IU/day (15 ug/day)

• Adults (>70 years): 800 IU/day (20 ug/day)

• UL: 4000 IU/day (100 ug/day)

Significant Sources: Sunlight, fortified milk and margarine, egg yolks, fatty fish and their oils (salmon, sardines)

Vitamin D Deficiency

• Overt signs of deficiency relatively rare, but inadequate vitamin D status

common

• Decreased production of proteins that promote uptake and transport of calcium

from GI system

• E.g., Calbindin (protein that binds to calcium in intestinal cells)

• Even when dietary calcium intake is adequate, it is not absorbed in GI tract,

leaving bones undersupplied

• Results in calcium deficiency

Rickets

(in children)

• Bones fail to calcify normally → growth impairments and skeletal abnormalities,

bones bend under weight (bowed legs – most obvious sign of disease), poorly

formed attachments of the bone to cartilage (protruding chest and belly, beaded

ribs)

• All breastfed healthy infants are supplemented with 400 IU of vitamin D/day,

infant formulas include vitamin D

Osteomalacia:

Deficiency of Vitamin D in adults

• Bones becomes increasingly soft, flexible, brittle, and deformed

Osteoporosis:

Inadequate synthesis or intake of vitamin D results in loss of calcium

from bones → porous bones → increased risk of fractures

Vitamin D Deficiency – Populations at Risk

Older Adults

• Skin, liver, and kidneys lose ability to make and activate vitamin D with age

• Dietary intake of vitamin D often low (i.e., milk)

• Less outdoor exposure, covered from sun – decreased vitamin D synthesis

• Recommended all older adults consume a vitamin D supplement (400 IU/day)

Northern Climates

• Less sun exposure, particularly during colder months, often covered for protection

and warmth

• Decreased synthesis of vitamin D

• Dark-skinned individuals in northern climates particularly at risk

Vitamin D Toxicity

Excess vitamin D from supplements can raise concentration of blood calcium

• Can result in kidney stones (body’s way of concentrating calcium for excretion)

• May harden blood vessels impacting major arteries in brain, heart, and lung

Magnesium function;

• Half of body’s magnesium is in the bones, rest is mostly in muscles and soft tissue, 1% in

extracellular fluid

Function

• Bone mineralization

• Heart functioning

• Role in energy metabolism → serves as enzyme in reaction creating ATP

• Works with calcium in muscle contraction and blood clotting → calcium promotes

contraction, magnesium inhibits it

• Calcium – muscle contraction, magnesium – muscle relaxation

• Helps maintain blood pressure and lung function

• Needed for synthesis of protein, fat, nucleic acids, and cell’s membrane transport

systems

Magnesium Recommendation (RDA, UL) and food sources:

• Recommendation (RDA, UL): (dont need to know)

• Men (19-30 years): 400mg/day

• Women (19-30 years): 310mg/day

• UL: 350mg non-food magnesium/day (supplements or magnesium salts)

• Food sources: “Hard” water, nuts, legumes, whole grains, dark green vegetables, seafood, chocolate,cocoa

Magnesium Deficiency

• Can make inflammation worse and contribute to chronic diseases

• Walls of arteries and capillaries tend to constrict – Increasing BP

• Can impair central nervous system

• Severe deficiency → results in tetany (similar to calcium tetany), possible hallucination

Magnesium and Hypertension

• Individuals living in places with “hard” water (high in calcium and magnesium), less

prevalence of heart disease

Mg Toxicity

Can be fatal – UL only applies to nonfood source

Fluoride function:

• Fluoride can replace the hydroxyl (OH) in hydroxyapatite crystal (calcium and phosphorus) to form fluorapatite

• Fluorapatite – makes bones stronger and teeth more resistant to decay

Fluoride Significant Sources:

Drinking water that is fluorinated, fish and most teas

Fluoride Deficiency:

Susceptible to tooth decay and dental carrie

Fluoride toxicity:

• Fluorosis: Discoloration and pitting of tooth

enamel caused by excess fluoride during

tooth development

• Mild case → small white specks

• Severe → pitted and permanently stained

teeth

• Occurs only during tooth development and

cannot be reversed

• Do not swallow fluoride containing dental

products (toothpaste, mouthwash

Vitamin K Function in bone health…

• Metabolism of bone proteins – Osteocalcin (Vitamin K needed to bind this protein to

minerals needed for bone formation)

• Adequate intake of Vitamin K helps decrease bone turnover and protect against fracture