title: Population-based study of age and sex differences in bone volumetric density, size, geometry, and structure at different skeletal sites.
abstract: In a population-based, cross-sectional study, we assessed age- and sex-specific changes in bone structure by QCT. Over life, the cross-sectional area of the vertebrae and proximal femur increased by approximately 15% in both sexes, whereas vBMD at these sites decreased by 39-55% and 34-46%, respectively, with greater decreases in women than in men.
  
  
  BACKGROUND
  The changes in bone structure and density with aging that lead to fragility fractures are still unclear.
  
  
  METHODS
  In an age- and sex-stratified population sample of 373 women and 323 men (age, 20-97 years), we assessed bone geometry and volumetric BMD (vBMD) by QCT at the lumbar spine, femoral neck, distal radius, and distal tibia.
  
  
  RESULTS
  In young adulthood, men had 35-42% larger bone areas than women (p < 0.001), consistent with their larger body size. Bone area increased equally over life in both sexes by approximately 15% (p < 0.001) at central sites and by approximately 16% and slightly more in men at peripheral sites. Decreases in trabecular vBMD began before midlife and continued throughout life (p < 0.001), whereas cortical vBMD decreases began in midlife. Average decreases in trabecular vBMD were greater in women (-55%) than in men (-46%, p < 0.001) at central sites, but were similar (-24% and -26%, respectively) at peripheral sites. With aging, cortical area decreased slightly, and the cortex was displaced outwardly by periosteal and endocortical bone remodeling. Cortical vBMD decreased over life more in women ( approximately 25%) than in men (approximately 18%, p < 0.001), consistent with menopausal-induced increases in bone turnover and bone porosity.
  
  
  CONCLUSIONS
  Age-related changes in bone are complex. Some are beneficial to bone strength, such as periosteal apposition with outward cortical displacement. Others are deleterious, such as increased subendocortical resorption, increased cortical porosity, and, especially, large decreases in trabecular vBMD that may be the most important cause of increased skeletal fragility in the elderly. Our findings further suggest that the greater age-related decreases in trabecular and cortical vBMD and perhaps also their smaller bone size may explain, in large part, why fragility fractures are more common in elderly women than in elderly men.
authors.affiliation: Endocrine Research Unit, Division of Endocrinology and Metabolism, Department of Internal Medicine, Mayo Clinic College of Medicine, 200 First Street SW, 5-194 Joseph, Rochester, MN 55905, USA. Riggs.Lawrence@Mayo.edu
authors.forename: B Lawrence
authors.initials: BL
authors.lastname: Riggs
authors.forename: L Joseph
authors.initials: LJ
authors.lastname: Melton Iii
authors.forename: Richard A
authors.initials: RA
authors.lastname: Robb
authors.forename: Jon J
authors.initials: JJ
authors.lastname: Camp
authors.forename: Elizabeth J
authors.initials: EJ
authors.lastname: Atkinson
authors.forename: James M
authors.initials: JM
authors.lastname: Peterson
authors.forename: Peggy A
authors.initials: PA
authors.lastname: Rouleau
authors.forename: Cynthia H
authors.initials: CH
authors.lastname: McCollough
authors.forename: Mary L
authors.initials: ML
authors.lastname: Bouxsein
authors.forename: Sundeep
authors.initials: S
authors.lastname: Khosla
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging; D015519:Bone Density; D005260:Female; D005272:Femur Neck / Q000473:pathology*; D006615:Hip / Q000473:pathology*; D006801:Humans; D008161:Lumbosacral Region / Q000473:pathology*; D008297:Male; D008593:Menopause; D008875:Middle Aged; D010024:Osteoporosis; D011884:Radius / Q000473:pathology*; D012737:Sex Factors; D013977:Tibia / Q000473:pathology*; D014057:Tomography, X-Ray Computed