aging of the skeleton: osteoporosis
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Aging of the Skeleton: Osteoporosis. An Evolutionary and Biocultural Perspective. Major Functions of the Skeleton. Body Support Body Movement Storage of Calcium and other minerals: Storage of Calcium provides upon request Calcium to blood. - PowerPoint PPT PresentationTRANSCRIPT
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Aging of the Skeleton: Aging of the Skeleton: Osteoporosis Osteoporosis
An Evolutionary and Biocultural Perspective
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Major Functions of the Skeleton• Body Support• Body Movement• Storage of Calcium and other minerals:
• Storage of Calcium provides upon request Calcium to blood.
• Blood Calcium is important for regulating numerous cellular activities
• Maintenance of Acid/Base balance in association with lungs and kidneys• Regulation and phosphate and carbonate for buffers
• Storage of bone marrow
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Skeleton Includes:
Bones
Tendons
Joints (or articulations)
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Structure & RemodelingOsteoblasts form new bones
Osteoclasts resorb old bones
Osteocytes carry on mature bone function
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Changes in bone strength with aging
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Calcium Metabolism
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Parathyroid Parathyroid hormonehormone
CalcitoninCalcitonin
CalcitriolCalcitriol
Vitamin DVitamin D33
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Major Hormones
• Parathyroid hormone increases bone resorption to mobilize calcium, thereby increasing plasma calcium
• Calcitonin increases intestinal calcium absorption and decreases renal excretion
• Calcitriol increases intestinal calcium absorption and increases renal excretion
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OsteoporosisOsteoporosis• A reduction in bone mass and deterioration bone
microstructure
• Clinically recognized as bone fragility with an increased susceptibility to fracture
• Osteopenia vs. osteoporosis
• Serious health concern in western aging populations: 1/2 women and 1/4 men > age of 50 will have an osteoporosis-related fracture. Women 4x times more likely than men
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OsteoporosisOsteoporosis• Bone mineral density (BMD)
WHO definition: BDM 2.5 SD’s below young adult mean
• Measured with densitometry
• Problems: population specific, overlap in fracture and non-fracture BMD, only looks at one measure of bone (quantity)
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OsteoporosisOsteoporosis
• Fractures hip, distal forearm, vertebral and hip fractures
• bone resorption > bone formation
QuickTime™ and aTIFF (Uncompressed) decompressor
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Bone• It is a rigid connective tissue• Organic (1/3) and Inorganic (2/3)
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Adult bone: dynamic, active and plasticAdult bone: dynamic, active and plastic
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Young normal
Elderly osteoporotic
Trabecular ArchitectureTrabecular Architecture
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Fragility FracturesFragility Fractures
Mays (1996)Mays (1996)
Roberts and Roberts and Manchester (1995)Manchester (1995)
• fragility fractures greater in females
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Etiology of Bone LossEtiology of Bone Loss Postmenopausal (Type I) and Age-related (Type II) Type 1: mostly in women; estrogen deficiency, rapid with menopause, spine, wrist Type 2: men also, slow, many sites esp. hip
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Age-related Bone LossAge-related Bone Loss• Senescence of osteoblasts (impaired
function)• Also increase in PTH levels (due to
decrease renal and Ca re-absorption and intestinal Ca absorption that occurs in elderly - as less Vit D exposure, less synthesis of calcitrol, or vitD resistance?)
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Multifactorial EtiologyMultifactorial EtiologyNumber of factors that play a role in
peak bone mass and loss: Genetics and ethnicity Lifestyle: alcohol, smoking, drugs diet/nutrition mechanical usage (physical activity) reproductive factors (pregnancy, parity and
lactation)
• Since multifactorial interest to look at its evolution and variation in different populations
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Osteoporosis in Past Osteoporosis in Past PopulationsPopulations
• Historical populations unique model to study bone loss• Many studies of bone loss in various archaeological
populations:
- pattern of bone loss and fragility in the past is different than in clinical osteoporosis today
- mostly bone mass
- few studies of bone quality
trabecular architecture
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Medieval ResultsMedieval Results
• Both sexes: significant change in trabecular architecture by middle age
• No sex difference• Low prevalence of fracture• Different patterns than seen in modern
populations
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• Nutrition/diet:- maybe sub-optimal conditions- no evidence for calcium or vitamin D deficiency - Vitamin D is likely important: Vitamin D insufficiency- Is Calcium really the big story in bone loss???
What is Going On?What is Going On?
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What is Going On?What is Going On?
• Physical activity:- rural farming population: both sexes
involved in similar arduous activity- Could have protected both sexes from
bone loss in old age
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What is Going On?What is Going On?Both diet and activity do not fully explain atypical patterns seen in females
•Reproductive Factors: pregnancy and lactation
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Pregnancy and LactationPregnancy and Lactation
• metabolically active states in bone• bone loss during pregnancy• long-term bone fragility? unlikely • With lactation recovery of bone loss• Evolutionary perspective: reproduction
should not be bad for skeleton
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Reproductive BehaviorsReproductive Behaviors Rural Medieval vs. Modern
• extended lactation (maybe also wet nursing) and later age at weaning
• parity (estimate 5-10 offspring)
• likely later menarche and slightly earlier menopause
=different hormonal environment
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PerspectivePerspective
• Cannot understand female bone maintenance without considering role of reproductive patterns
• In taking this approach we improve our understanding of the disease today
• Osteoporosis is a heterogeneous disorder: lifestyle factors clearly important
• A combined biocultural, evolutionary and life history approach is vital to get at natural history of bone loss and fragility