Cross-sectional versus longitudinal evaluation of bone loss in men and women

We evaluated age- and sex-specific differences in bone density at a variety of skeletal sires in a population-based sample of 348 men (age 22-90 years ) and 351 women (age 21-93 years) by dual-energy X-ray absorptiometry. Seve ral patterns of age-related bone loss were observed, but adjustments for he ight (or, where possible, calculation of bone mineral apparent density) dam pened the apparent rate of bone loss from most skeletal sites as judged fro m cross-sectional measurements at baseline. Cross-sectional data also overe stimated the rate of bone loss observed longitudinally over 4 years at many sites, particularly the hip and spine: conversely, in some forearm regions , cross-sectional rates of loss underestimated the bone loss seen prospecti vely. Longitudinal rates of bone loss were generally greater among individu als age 70 years or older compared with younger men and women, but some of the latter effect was due to a greater proportion of younger women on hormo ne replacement therapy, whose rate of bone loss was generally less. These o bservations highlight the limitations of cross-sectional data for defining the patterns of bone loss over life at different skeletal sites.