Background: Decreased lean mass in aging, is becoming a serious health problem. However, whether this phenomenon is confined to the elderly or different according to gender, is controversial. In this study, we aimed to analyze the risk for rapid decrease in lean mass according to age and gender in relative young Korean adults over four years of follow-up.
Method: In 65,856 non-diabetic participants (59.5% men, mean age 39.1 years) in a health screening program, body composition analyses by bioimpedance analysis method and all the metabolic parameters were repeatedly performed at baseline and after four years. Subjects were divided into two groups with the age cutoff of 50 yrs and into four age groups (<40, 40-49, 50-60, >60 years old). In addition, the subjects were divided into six groups according to age older or young than 50 yrs and body weight change degree (<-5, -5~5, >5%) over four years. Analyses were performed with actual changes of body weight, lean mass and fat mass and their percent change over four years.
Results: In every age and sex group, percent change of lean mass decreased and percent change of fat mass showed positive change as the subjects got older. However, percent decrease in lean mass and percent increase in fat mass per year were significantly higher in women compared with men (-0.26 vs. -0.15%, 0.34 vs. 0.42%, p<0.01). Those who were older than 50 yrs and who showed weight loss (<-5%) over four years showed significantly higher decrease in lean mass and lower decrease in fat mass compared to those who were younger than 50 yrs old. When the odds ratio (OR) for being in the lowest quartile of percent change of lean mass according to age group were analyzed in different gender, women showed higher risk for being in the lowest quartile of percent change of lean mass as they got older compared to men after adjustment for confounding factors (1.202, 1.768, 2.855 vs. reference (30s) in women; 1.082, 1.553, 2.249 vs. reference (30s) in men).
Conclusion: Even in this young study population, lean mass significantly decreased as they age, and the risk for fast decrease in lean mass was higher in women compared with men.

Change of body composition according to age and gender in young non-diabetic Korean subjects