BONE MASS THROUGH THE LIFE CYCLE
-up to age 20 - active bone growth
-mid 20s-30 = peak
-mid 30s - begin to lose bone mass
-women lose more becasue of menopause -follicles desintegrating rapidly and become insensitive to hormones -not making estrodiol or progesterone -lose 1% per year
BONE REMODELING
-osteoclasts dissolve bone
-osteoblasts lay down protein and then minerals bind to proteins to make bone hard -calcium, phosphorus adhere to protein matrix layed down by osteoblasts -takes months to make new bone -osteoblasts change after protein is laid down -migrate inside bone and put out 'tentacles' - extend out osteocytes -osteocytes derived from osteoblasts -detect any force exerted on the bone (ex. running) -stimulate bone formation/increase/maintain bone density -not actually involved in bone remodeling -most cells in bones are osteocytes
-bone is not like skin in that new cells replace old cells
-happens in little pockets/individual units (not across whole bone)
-completely replace bone in 10 years*** -constantly breaking down and making bone -very dynamic process -as you get older, bone resorption increases while bone formation decreases
-teeth not included in this process
OSTEOPOROSIS
-bone loss with age
-seen especially with white women
-25 million people affected
-due to loss of estrogen and/or inadequate intake of calcium -also maybe not getting enough vitamin D
-bones become more porous
-become susceptible to fractures
-estrogen has positive effect on bones; keeps them dense* -when you lose estrogen, don't have that protection
RISK FACTORS - NON MODIFIABLE (can't do anything about them)
-older age - strongest predictor -if men get it, is after 75
-female
-women have 40% chance, men have 13%
-early menopause = lower bone density earlier, continue losing bone
-race - white women -black women have more dense bones
-genetics
-family history
RISK FACTORS - MODIFIABLE
-body weight -weigh 127 or lower, increased risk -high body fat will sequester the vitamin D they're making and render it unavailable for activation -women who are very thin don't make as much estrogen, need fat, more susceptible
-important to do weight bearing exercises to maintain bone density
-nutrient intake - get enough calcium in the diet, at least get RDA for your age group -need more calcium around postmenopause
-smoking -> low body weight -smoking can damage osteoblasts
-high caffeine intake - drinking coffee instead of milk, low bone density
-alcohol abuse - excrete calcium and magnesium more
-some medications -thyroid hormone - at increased risk -anticoagulants - heart patients -corticosteroids - some kind of autoimmune problem -antidepressants - seratonin uptake inhibitors?
CHART
-woman A has higher bone density than B during adulthood
-start losing gradually at first, then menopause
-woman A had no problem because she started with a lot of bone mass
-dangerzone = osteopenia (not osteoporosis, but less than desired)
-arounnd age 70 has osteoporosis

-1 out of 2 white women will experience some kind of osteoporatic fracture sometime during her life
-as age increases, so does risk of osteoporosis
BONE DENSITOMETRY
-DEXA scan used for determining body fat, but also bone density -dual energy x-ay absorptiometry
-sit there from 10-20 minutes, get a T-score -lower T-score, more likely to get a fracture
-best way to measure
-trabecular bone is inside bone
-cortical bone is stronger, along edges
-lose more trabecular bone than cortical
T-score is expressed as standard deviations above or below the mean healthy person at age 30 -everyone compared against that -above and