Men With Subclinically Low Bone Mass Exhibit Lower IGF-1 And Lean Mass Than Normal Controls

PURPOSE: Compare hormone concentrations, systemic markers of bone metabolism, and body composition between healthy young adult males with lower versus normal bone mineral density (BMD). METHODS: Young adult males with lower than expected areal BMD (aBMD; LOW; Z-score < -1 any site; n = 21) compared to higher than average aBMD controls (CON; Z-score 1 any site but not < -1 at any site; n = 18) were included based on BMD guidelines by the American College of Sports Medicine. aBMD of the total body, hip, femoral neck, and lumbar spine, and body composition were obtained using dual-energy x-ray absorptiometry. Total testosterone, tartrate resistant acid phosphatase 5 beta, procollagen 1 N-propeptide, bone alkaline phosphatase, insulin like growth factor-1, sclerostin, beta-c-terminal telopeptide, parathyroid hormone, and estradiol were determined from blood samples after an overnight fast using ELISA. Independent samples t-tests, or non-parametric alternatives, were used to determine group differences, α = 0.05. RESULTS: The LOW group was older (LOW: 26 ± 5 yrs; CON: 23 ± 5 yrs; p = 0.037) but exhibited similar body mass index to the CON group (LOW: 24.5 ± 3.5 kg/ m2; CON: 23.8 ± 2.6 kg/ m2; p = 0.459). Among LOW, 14 subjects (66.7%) had a Z-score < -1 at more than one BMD site. Total body lean mass (LBM) was lower in LOW vs. CON (MD = -6.1 kg, p = 0.003). IGF-1 concentrations were lower in LOW vs. CON (MD = -74.97 ng/ mL, p = 0.027). No group differences were observed for fat mass or other biomarkers (all p ≥ 0.064). CONCLUSIONS: Young men with lower aBMD had lower LBM and circulating IGF-1 than those with normal BMD. Attenuated IGF-1 may have directly contributed to lower BMD via actions on osteoblasts to stimulate longitudinal bone growth or possible indirect actions through its influence on skeletal muscle, which may result in decreased gravitational loading via reduced LBM and body mass. LBM represents a modifiable, early lifestyle factor for improving bone health. Supported by: DoD W81XWH2110542