title: Age-related differences in body composition by hydrodensitometry and dual-energy X-ray absorptiometry.
abstract: To determine whether percent body fat (%BF) is overestimated in older people by hydrodensitometry (HD) because of an age-related decrease in bone mineral content (BMC), body composition of 113 women and 72 men (21-81 yr) was assessed by HD and dual-energy X-ray absorptiometry (DEXA). DEXA provides an estimate of %BF adjusted for differences in BMC. HD %BF and DEXA %BF were not different in young people [21-39 yr; 17.6 +/- 6.4 (SD) vs. 17.6 +/- 7.2%, NS], were slightly, but significantly, different in middle-aged people (40-59 yr; 25.5 +/- 6.4 vs. 24.1 +/- 6.7%, P < 0.05), and showed the largest disparity in older people (> or = 60 yr; 34.9 +/- 7.9 vs. 30.8 +/- 8.7%, P < 0.05). The discrepancy in older people was apparently not due to mineral loss, however, inasmuch as correction of HD %BF for variance in BMC as a fraction of fat-free mass resulted in only small adjustments (approximately 1%) of %BF. Assessment of DEXA %BF was further evaluated in nine subjects with packets of lard (2-3 kg) overlying either the thigh or the trunk region. Only 55% of the exogenous fat was identified as fat when it was in the trunk region compared with 96% when it was positioned over the legs. These data suggest that the age-related increase in upper body adipose tissue is underestimated by DEXA.
authors.affiliation: Section of Applied Physiology, Washington University School of Medicine, St. Louis, Missouri 63110.
authors.forename: D B
authors.initials: DB
authors.lastname: Snead
authors.forename: S J
authors.initials: SJ
authors.lastname: Birge
authors.forename: W M
authors.initials: WM
authors.lastname: Kohrt
mesh_terms: D015502:Absorptiometry, Photon; D000273:Adipose Tissue / Q000033:anatomy & histology / Q000502:physiology; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D001823:Body Composition / Q000502:physiology*; D001835:Body Weight / Q000502:physiology; D015519:Bone Density / Q000502:physiology; D003720:Densitometry; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012727:Sex Characteristics