Factors Associated with Changes in Skeletal Muscle Mass in Medical Health Checkups

Background/Objectives: To explore the factors associated with changes in skeletal muscle mass among Japanese health checkup subjects (5214 men and 6614 women). Methods: Fat-free index (FF index) was defined as FF mass divided by height squared (kg/m²). Change rate in FF index (kg/m²/year) was defined as [FF index (second time) - FF index (first time (i.e., baseline))]/interval between first and second times (years). Factors associated with change rate in FF index >0 kg/m²/year were primarily examined. Results: The average age, body mass index (BMI) were 52.4 years and 23.9 kg/m² for men, and 50.5 years and 21.8 kg/m² for women. In the multivariate analyses, age (p < 0.0001), body mass index (BMI, p < 0.0001), baseline FF index (p < 0.0001), waist circumference (p = 0.0365), fasting blood sugar (FBS, p = 0.0012), alanine aminotransferase (p < 0.0001) and alcohol intake were found to be significant in men, while BMI (p < 0.0001), baseline FF index (p < 0.0001), triglyceride (p = 0.0031), FBS (p = 0.0064) and alcohol intake were found to be significant in women. Conclusions: Lifestyle guidance from various aspects including metabolic factors may be important to maintain skeletal muscle mass.