Date Published: March 8, 2019
Publisher: Public Library of Science
Author(s): Thibault Sutter, Hechmi Toumi, Antoine Valery, Rawad El Hage, Antonio Pinti, Eric Lespessailles, Masaki Mogi.
Although the relationship between body composition and bone mineral density (BMD) is well established, the relative contribution of appendicular lean mass (ALM) and fat mass (FM) to BMD has been rarely evaluated in young men.
We assessed 100 young men (age: 24.4±2.8 years, BMI: 23.4±2.81 kg/m2). Appendicular lean mass index (ALM/H2) (ALMI), fat mass index (FM/ H2) (FMI), percentage of body fat, BMD at lumbar spine (LS), total hip (TH), femoral neck (FN) and whole body (WB) were measured using DXA. Muscle strength was evaluated by handgrip strength. Pearson’s correlations and interactions between all variables were assessed using stepwise regression analyses.
ALM index (ALMI) was positively correlated with BMD at all sites (r = 0.62 for WB p<0.05, r = 0.54 for FN p<0.05, r = 0.64 for TH p<0.05, r = 0.56 for LS p<0.05) whereas FMI was not correlated to BMD values. Stepwise regression analyses showed that ALMI produced a significant and positive influence on BMD (β = 0.07 for WB p<0.001, β = 0.04 for FN p<0.001, β = 0.06 for TH p<0.001). Conversely, FMI was negatively associated with BMD at all sites (β = -0.02 for WB p<0.001, β = - 0.03 for FN p<0.001, β = - 0.03 for TH p<0.001, β = - 0.07 for LS p<0.001). Handgrip strength and BMDs were significantly and positively associated at all sites. Our data suggest that BMD was positively associated with ALMI while negatively with FMI. We confirm that ALMI is the strongest factor associated with BMD in a population of young men.
Illustrating muscle-bone [1,2] and fat-bone interactions  changes in body composition occur throughout life. These changes have important metabolic and functional consequences as illustrated in cachexia and sarcopenia [4,5]. In addition, changes in body composition including lean mass anf fat mass lead to bone changes in aging population that can lead to sarcopenic obesity and osteoporosis through multifactorial and complicated relationships [6–8].
Our study confirmed that among the body composition variables and baseline anthropometric characteristic, ALMI was consistently a significant and positive independent contributor to whole body and hip BMD in healthy young men aged 20 to 30 years. Lean body mass has been found to be positively correlated with BMD in women of different age groups [28–31]. In men, our findings are consistent with most previous studies on the relationships between body composition and BMD showing in multivariate linear regression models that lean mass is uniquely associated with the largest proportion of variance of WBBMD [6,10,32,33]. Blain et al. showed  that ALMI was the most significantly correlated factor (r = 0.39, p <0.0001) and associated (β = 0.00283, p <0.0001) to the FN BMD. Verschuren et al. found that ALMI was also strongly associated with all bone sites (β = 0.317, p <0.001 for WBBMD, β = 0.3730, p <0.001 for FN, β = 0.433, p <0.001 for TH, β = 0.294, p <0.001 for LS) . However, in older populations the appendicular skeletal muscle mass factor explains between 15% to 20% of the variability at the femoral neck [32,33]. The positive association between ALMI and BMD might reflect the direct mechanical effects (muscle contractions and resulting movements) of muscle tissue on bone through their regulation by both genetic and life style factors such as physical activity . Source: http://doi.org/10.1371/journal.pone.0213681