Comparison of body composition between thin and normal-weight sarcopenic children: a single-center, propensity score matching analysis of a large-scale study.

OBJECTIVE

This study aims to investigate the incidence of sarcopenia in thin and normal-weight children and analyze their body composition differences.

METHODS

Body composition was assessed using bioelectrical impedance analysis (BIA) in children who visited the Department of Child and Adolescent Healthcare at the Children’s Hospital of Soochow University between September 2016 and September 2024. Sarcopenia was defined as a skeletal muscle mass index (SMMI) at or below the 3rd percentile, and classified as thin sarcopenia or normal-weight sarcopenia based on international body mass index (BMI) cutoff values. Propensity score matching (PSM) balances baseline characteristics, including age and sex.

RESULTS

A total of 41,872 children underwent body composition assessment, of whom 1,546 (3.70%) were diagnosed with sarcopenia. After PSM, the final analysis included 367 normal-weight children with sarcopenia and 734 thin children with sarcopenia. Compared to children in the normal-weight sarcopenia group, those in the Thin Group were significantly taller (P < 0.05), but had lower body weight and body fat levels (P < 0.001). No significant differences were found between the two groups in protein content, inorganic salts, muscle mass, lean mass, skeletal muscle mass, or bone mineral content (P > 0.05). Children in the Thin Group had a higher percentage of skeletal muscle mass, relative muscle content, and muscle-to-fat ratio than the Normal Weight Group (P < 0.001). Similarly, the proportion of fat-free mass (FFM) in the extremities was significantly lower in the Thin Group compared to the Normal Weight Group (P < 0.001).

CONCLUSION

The coexistence rate of sarcopenia and thinness is high. The normal-weight children also require body composition analysis to identify occult sarcopenia. Sarcopenia of different body types presents two distinct physical phenotypes, which may involve different pathological mechanisms and interventions. TRIAL REGISTRATION: Not applicable.