Location: Obesity and Metabolism Research Unit
Title: THE RELATIVE CONTRIBUTION OF LEAN TISSUE MASS AND FAT MASS TO BONE DENISTY IN YOUNG WOMEN Authors
|Wang, May - UC BERELEY|
|Bachrach, Laura - STANFORD UNIVERSITY|
|Van Loan, Marta|
|Hudes, M - UC BERKELEY, SCI TOXICOLO|
|Flegal, K - UC BERKELEY|
|Crawford, Patricia - UC BERKELEY|
Submitted to: Bone
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 25, 2005
Publication Date: April 29, 2005
Citation: Wang, M.C., Bachrach, L.K., Van Loan, M.D., Hudes, M., Flegal, K.M., Crawford, P.B. 2005. THE RELATIVE CONTRIBUTION OF LEAN TISSUE MASS AND FAT MASS TO BONE DENISTY IN YOUNG WOMEN. Bone. 37:474-481. Interpretive Summary: Obesity is associated with a number of chronic diseases such as hypertension and diabetes, but generally not osteoporosis. Although chronic dieting has been shown to impact bone density in adult women and more recently evidence has suggested that in children and adolescents, obesity may be associated with a lower bone density, after adjusting for body weight. This study measured the bone density of 921 young adult women, 21- 25 years of age and examined the relationships between lean mass, fat mass and young adult bone mass. We found that lean mass, the active muscle mass of the body, was positively related to bone density; the more lean mass the higher the bone density. Fat mass also had a positive effect on bone but smaller than that of lean mass. So, for a set amount of body weight an individual with more fat mass will have a lower bone density. Given the obesity epidemic in the US, these data suggest that young adult women with less lean mass and more fat mass with have a lower bone density; potentially leading to early onset of osteoporosis.
Technical Abstract: Although obesity is associated with increased risk of many chronic diseases including cardiovascular disease, diabetes, hypertension, and cancer, there is little evidence to suggest that obesity increases risk of osteoporosis. In fact, both weight and Body Mass Index are positive predictors of bone mineral density in adults, suggesting that those who are overweight or obese may be at lower risk of osteoporosis. However, recent evidence suggests that in children and adolescents, obesity may be associated with lower rather r=than higher weight-adjusted bone density. We investigated the associations of adiposity (defined by fat mass in kg) as well as lean tissue mass with various measures of bone mass in an ethnically diverse group of 921 young women, aged 20-25 years (331 African Americans, 154 Asians, 328 Caucasians, and 128 Latinas). Bone mass, fat mass and lean tissue mass were measured using dual energy x-ray absorptiometry (GE Lunar Corp., Madison, WI). Bone mass was expressed as BMD (g/c,2) and BMAD (g/cm3) for the spine and femoral neck, and as BMD and BMC 9g) for the whole body. Simultaneous regression analysis was sued to examine: 1) in separate regressions, the association of lean tissue mass and fat mass with each one mass parameters, controlling for weight; and 2) in the same regression, the independent contribution of lean tissue mass and fat mass to bone mass. Consistent wit the findings of other studies, lean tissue mass was positively correlated with all measures of bone mass. Fat mass was found to be positively associated with bone density when weight was not controlled for, and negatively associated with bone density when weight was controlled for. We found that both fat mass and lean tissue mass had positive associations with bone density, but effects of fat mass on bone density was smaller than that of lean tissue mass. Since the effect of lean tissue mass is greater than that of fat mass, the increase in bone density due to increasing fat mass is offset by the decrease in bone density due to decreasing lean tissue mass and the net result is that, when weight is held constant, fat mass often appears to be negatively associated with bone density. Given the increasing prevalence of obesity, these findings have important implications for bone health in young women.