Trunk fat negatively influences skeletal and testicular functions in obese men: clinical implications for the aging male

Abstract

Osteocalcin (OSCA) seems to act as a negative regulator of energy metabolism and insulin sensitivity. Evidence from male rodents suggests that OSCA may also regulate testosterone (T) synthesis. Using a cross-sectional design, we evaluated OSCA, 25(OH) vitamin D, T, 17 β -estradiol (E2), homeostasis model assessment of insulin resistance (HOMA-IR), and body composition in 86 obese (mean BMI = 34) male subjects (18-69 yr old). Independently from BMI, an inverse relationship between trunk fat percentage and plasma T (r (2) = -0.26, P < 0.01) and between HOMA-IR and OSCA levels (r (2) = -0.22, P < 0.005) was found. OSCA levels, as well as vitamin D, decreased significantly for higher BMI with significant differences above 35 (P < 0.01). A direct correlation between T and bone mineral density at lumbar (BMDL) and neck (BMDH) (P < 0.001, r (2) = -0.20; P < 0.001, r (2) = -0.24) was found, independently from age. An inverse correlation between E2 levels, BMDL, and BMDH (P < 0.001, r (2) = -0.20; P < 0.001, r (2) = -0.19) was observed. These data provide new evidences that a relationship between trunk fat mass, insulin sensitivity, OSCA and T synthesis occurs. This new relationship with skeletal health has relevant implications for the aging male, suggesting OSCA as a novel marker of metabolic and gonadal health status.

Figure 1

Correlation between (a) total testosterone (total T) and trunk fat (TF) (P < 0.01, r ² = −0.26), (b) osteocalcin (OSCA) and TF (P < 0.001, r ² = −0.17), (c) OSCA and Total T (P < 0.0001, r ² = 0.23), (d) OSCA and HOMA (P < 0.001, r ² = −0.20).

Figure 2

Correlation between (a) total testosterone (total T) and lumbar bone mineral density (BMDL) (P < 0.001, r ² = −0.20), (b) 17β-estradiol and BMDL (P < 0.001, r ² = −0.20), (c) total T and hip BMD (BMDH) (P < 0.001, r ² = −0.24), (d) 17β-estradiol and BMDH (P < 0.001, r ² = −0.19).