title: Gender comparison of factors associated with age-related differences in bone mineral density.
abstract: We found that age-related decline in bone mineral density (BMD) is more pronounced in women than in men, that lean mass was the most important determinant of BMD in all age groups in both sexes, and that different factors may be important for bone health of men and women and at different ages.
  
  
  BACKGROUND
  Multiple factors may affect bone mineral density (BMD). Our objective was to identify the correlates of age-related differences in BMD among men and women.
  
  
  METHODS
  We performed a cross-sectional study involving 490 men and 517 women between the age of 29 and 87 years that were free of medication and diseases known to affect bone metabolism. BMD was measured at various sites using dual-energy X-ray absorptiometry, and factors possibly associated with skeletal status were assessed by direct measurements and a detailed questionnaire.
  
  
  RESULTS
  BMD was lower with advancing age at all BMD measurement sites, the greatest difference being for the femoral neck where in women BMD was 37.5 % lower in the oldest compared to that in the youngest age group, but the difference was 22.9 % in men. Levels of free estradiol were sharply lower after age of 40 among women; free testosterone declined gradually with age among men but was not independently associated with BMD. Factors including lean mass, physical activity, ionized calcium, C-terminal telopeptide (CTX), serum sodium, free estradiol, and smoking explained a large fraction of difference in BMD in different age groups but to a varying degree in men and women. Lean mass was the strongest independent factor associated with BMD at all sites among men and women.
  
  
  CONCLUSIONS
  Age-related decline in BMD is more pronounced in women than in men, but determinants of BMD are multiple and interrelated. Our study indicates that different factors may be important for bone health of men and women and at different ages.
authors.affiliation: School of Medicine, University of Iceland, Reykjavik, Iceland.
authors.forename: Hrafnhildur L
authors.initials: HL
authors.lastname: Runolfsdottir
authors.forename: Gunnar
authors.initials: G
authors.lastname: Sigurdsson
authors.forename: Leifur
authors.initials: L
authors.lastname: Franzson
authors.forename: Olafur S
authors.initials: OS
authors.lastname: Indridason
mesh_terms: D015502:Absorptiometry, Photon; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D015519:Bone Density / Q000502:physiology*; D002118:Calcium / Q000097:blood; D003430:Cross-Sectional Studies; D004958:Estradiol / Q000097:blood; D005260:Female; D005272:Femur Neck; D006801:Humans; D008297:Male; D008875:Middle Aged; D012737:Sex Factors; D013739:Testosterone / Q000097:blood
chemical_list: D013739:Testosterone; D004958:Estradiol; D002118:Calcium