Food and Nutrition Ch 14: Bone health

Cortical (compact bone)

• very dense

• provides strength on outer length of long bones and main tissue of smaller bones

Trabecular (spongy bone)

• less dense

• responds to changing hormone levels and more readily releases minerals

Composition of bones

65% inorganic matter (mineral crystals deposited into collagen)

• provides strength and structural support

35% organic matter (collagen protein)

• allows flexibility in bones

Bone mineral density

measure of how tightly mineral crystals are packed into protein matrix

• indicator of bone strength

Osteoporosis

disease caused from excessive loss of bone —> porous and fragile bones —> increased risk of fractures and breaks

Osteoclasts

cells in bone that break down bone during growth

Osteoblasts

cells in the bone that rebuild bone during growth

Bone remodeling

reshaping of the bone

• over time, osteoclasts stay active, osteoblasts reduce in activity —> bone loss

Factors that influence bone health

• nutrition (intake of vitamin D, calcium, protein intake)

• weight bearing exercises

• alcohol intake

• smoking

• stress

• sleep

• body weight

• genetics

• age

Calcium function

• stored in bones

• form hydroxyapatite crystals (calcium + phosphorus) in bones

• protects against hypertension

Low blood calcium

parathyroid hormone gland secretes parathyroid hormone, hormone stimulates Vitamin D

• In kidneys Parathyroid hormone and vit D stimulate calcium reabsorption into the blood

• In intestines Vit D enhance calcium absorption

• In bones Vit D and parathyroid hormone stimulate osteoclast cells to break down bone releasing calcium

High blood calcium

thyroid gland secretes calcitonin

• In kidneys: calcitonin inhibits Vit D activation and prevents reabsorption of Ca

• Intestines: limits calcium absorption (by inhibiting Vit D)

• In bones: inhibits osteoclast cells from breaking down bone

Calcium absorption

• adults absorb ~30% of calcium digested

• pregnant women absorb 50%

• young children and teens absorb 50-60%

Calcium absorption enhancers

• stomach acid

• Vitamin D

• Lactose (in infants)

Calcium absorption inhibitors

• Vitamin D deficiency

• lack of stomach acid

• high phosphorus intake

• phytates (grains)

• oxalates

Calcium balance

too much —> calcium rigor

• hardness or stifness of muscles

too little —> calcium tetany

• uncontrolled muscle contractions, spasms

Food sources of calcium

• milk products

• fortified plant based milk alternatives

• sardines with bones

• tofu with calcium salt

• tahini

• broccoli

• cabbage

Calcium deficiency

• stunted growth in children

• osteoporosis

Calcium toxicity

• from supplementation

• constipation

• increased risk of kidney stones

• interference with absorption of other minerals

Phosphorus recommendations

RDA: 700mg/day

UL: 4000mg/day

Phosphorus deficiency and toxicity

Deficiency: very rare, muscular weakness, bone pain

Toxicity:

• calcification of non-skeletal tissues, kidneys

• increased Ca excretion from bones

  • detrimental to bones and teeth

Phosphorus food sources

• protein rich food

• milk

• salmon

• navy beans

• soft drinks/pop

How the body synthesizes Vitamin D

• sunlight hits precursor in skin —> 7-dehydrocholesterol (7-DC)

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

• Liver and kidney convert precursor to active 1. 25 hydroxyvitamin D3

• Active form of Vitamin D is a hormone - has a binding protein to be carried around body (Vitamin D binding protein DBP)

Vitamin D function

• bone growth: assist in absorption of Ca and P

• raises blood concentration

  • vit D enhances absorption of needed minerals from GI tract

  • when diet is insufficient, reabsorption of minerals in kidneys

  • mobilization of minerals from bones to blood

• connected to immune system, nervous system, pancreas, skin, muscle, cartilage, reproductive organs

Sources of vitamin D

• sunlight

• fortified milk

• margarine

• egg yolk

• fatty fish

• oils

Vitamin D recommendations

RDA: 600 IU/day

Vitamin D deficiency

• decrease in proteins that promote uptake and transport of Ca from GI system (ex: calbindin)

• Rickets

• osteomalacia: in adults: bones become soft

• Osteoporosis: inadequate synthesis or intake of Vit D, loss of calcium from bones

Rickets

in children

• bones fail to calcify —> skeletal abnormalities

  • bowed legs, beaded ribs

factors in sun exposure

• sunscreen

• melanin in skin

• time of day/season

• geographical location

• smoke, cloud, smog

• latitiude

Populations at risk for Vitamin D deficiency

• older adults

  • lose ability to make vit D

• Northern climates

Vitamin D toxicity

from supplements

• raise concentration of blood calcium —> kidney stones, harden blood vessels

Magnesium function

• bone mineralization

• heart functioning

• energy metabolism

• works with calcium in muscle contraction and blood clotting magnesium INHIBITS it

Magnesium recommendation

RDA

men: 400mg/day

women: 310mg/day

UL: 350mg (supplements)

Magnesium food sources

• hard water

• nuts

• legumes

• whole grain

• dark green vegetables

• seafood

• chocolate

• cocoa

Magnesium deficiency

• make inflammation worse, contribute to chronic disease

• wall of arteries and capillaries constrict (raise BP)

Fluoride function

replace hydroxyl (OH) in hydroxyapatite crystal to from fluorapatite

• makes bone stronger and teeth more resistant

Fluoride sources

fluorinated water, fish, teas

Fluoride recommendations

AI

men: 4mg/day

women: 3mg/day

UL: 10mg/day

Fluoride deficiencies

• dental carries

Fluoride toxicity

fluorosis: discoloration and pitting of tooth enamel during tooth development

• mild case —> small white specks

• severe —> pitted permanently stained teeth

Non modifiable Risk factors of osteoporosis

• older age

• female

• white, asian, hispanic heritage

• small frame

• maternal history

• estrogen deficiency

modifiable Risk factors of osteoporosis

• sedentary lifestyle

• inadequate calcium/vit D

• excessive protein, sodium, caffeine, alcohol

• smoking

• certain medications

• low BMI