Relationship of obesity with osteoporosis.
BACKGROUND
The relationship between obesity and osteoporosis has been widely studied, and epidemiological evidence shows that obesity is correlated with increased bone mass. Previous analyses, however, did not control for the mechanical loading effects of total body weight on bone mass and may have generated a confounded or even biased relationship between obesity and osteoporosis.


OBJECTIVE
The objective of this study was to reevaluate the relationship between obesity and osteoporosis by accounting for the mechanical loading effects of total body weight on bone mass.


METHODS
We measured whole body fat mass, lean mass, percentage fat mass, body mass index, and bone mass in two large samples of different ethnicity: 1988 unrelated Chinese subjects and 4489 Caucasian subjects from 512 pedigrees. We first evaluated the Pearson correlations among different phenotypes. We then dissected the phenotypic correlations into genetic and environmental components with bone mass unadjusted or adjusted for body weight. This allowed us to compare the results with and without controlling for mechanical loading effects of body weight on bone mass.


RESULTS
In both Chinese and Caucasian subjects, when the mechanical loading effect of body weight on bone mass was adjusted for, the phenotypic correlation (including its genetic and environmental components) between fat mass (or percentage fat mass) and bone mass was negative. Further multivariate analyses in subjects stratified by body weight confirmed the inverse relationship between bone mass and fat mass, after mechanical loading effects due to total body weight were controlled.


CONCLUSIONS
Increasing fat mass may not have a beneficial effect on bone mass.
Zhao
Lan-Juan
LJ
Department of Orthopedic Surgery, School of Medicine, University of Missouri-Kansas City, 2411 Holmes Street, Kansas City, MO 64108, USA.
Liu
Yong-Jun
YJ
Liu
Peng-Yuan
PY
Hamilton
James
J
Recker
Robert R
RR
Deng
Hong-Wen
HW
D000328:Adult; D000368:Aged; D044466:Asian People; D001696:Biomechanical Phenomena; D001823:Body Composition / Q000502:physiology; D015992:Body Mass Index; D001835:Body Weight / Q000502:physiology; D002681:China / Q000453:epidemiology; D005006:Ethnicity; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000150:complications* / Q000503:physiopathology; D009929:Organ Size / Q000502:physiology; D010024:Osteoporosis / Q000150:complications* / Q000503:physiopathology; D010641:Phenotype; D012727:Sex Characteristics; D014481:United States / Q000453:epidemiology; D044465:White People