Body Composition and S-Klotho Plasma Levels in Middle-Aged Adults: A Cross-Sectional Study

The α-Klotho gene was identified as a possible "aging-suppressor" agent that extends life span when overexpressed. However, little is known about the association of the body composition with the secreted protein form of the α-Klotho gene (S-Klotho). Therefore, the aim of this study was to analyze the association of body composition, including lean and fat mass as well as bone mineral density (BMD), with S-Klotho plasma levels in middle-aged sedentary adults. A total of 74 (39 women) middle-aged sedentary adults (53.7 ± 5.1 years old; 75.7 ± 14.0 kg; 167.8 ± 9.8 cm) participated in the study. We measured weight and height, and we used dual-energy X-ray absorptiometry to measure fat mass and lean mass. We calculated the body mass index (BMI), fat mass index (FMI), and lean mass index (LMI). The S-Klotho plasma levels were measured in the ethylenediaminetetraacetic acid plasma using a solid-phase sandwich enzyme-linked immunosorbent assay. There was a strong positive association between LMI and S-Klotho plasma levels (β = 74.794, R² = 0.346, p < 0.001), which persisted after controlling for age and gender as well as after additionally controlling for FMI. Significantly positive associations of BMI and BMD were also found with S-Klotho plasma levels (β = 33.981, R² = 0.125, p = 0.002 and β = 858.194, R² = 0.058, p = 0.041, respectively), which disappeared after controlling for LMI (β = 0.183, R² = 0.611, p = 0.984 and β = -379.426, R² = 0.617, p = 0.290, respectively). FMI was not significantly associated with S-Klotho plasma levels. Our study shows that LMI is strongly associated with S-Klotho plasma levels and explains the associations of BMI and BMD with S-Klotho plasma levels in middle-aged sedentary adults.