Relationship between near-infrared spectroscopy, and subcutaneous fat and muscle thickness measured by ultrasonography in Japanese community-dwelling elderly

Aim: Near-infrared spectroscopy (NIRS) allows estimation of the percentage of body fat (%BF) regardless of the patient's posture; thus, it is useful for assessment of elderly patients with severe decline of basic activity who cannot hold a standing position. However, the accuracy by which the near-infrared light emitted from NIRS reflects subcutaneous tissue is unknown. The aim of this study was to assess how correctly NIRS reflects the subcutaneous fat and muscle thickness derived from ultrasonography in community-dwelling elderly. Methods: A total of 93 community-dwelling older adults aged 65years and older were enrolled in this study (mean 75.8years, 6.7 SD). Participants were assessed according to optical density (OD) measurements by NIRS, subcutaneous fat and muscle thickness by ultrasonography, and muscle strength. Pearson's correlation coefficients were calculated for each sex. Stepwise multiple regression analysis was used to identify factors that contributed to OD for each sex. Results: OD measured at the forearm and thigh were significantly correlated with subcutaneous fat thickness. In stepwise multiple regression analyses, subcutaneous fat thickness was found to be a significant determinant of OD in men (forearm =0.37, P=0.01; thigh =0.63, P<0.001) and women (forearm =0.50, P<0.001; thigh: =0.52, P<0.001). Conclusions: These results suggest that NIRS can appropriately estimate fat-free mass. By adding other variables to OD as the predictive variable, skeletal muscle mass might be estimated in the elderly population. Geriatr Gerontol Int 2013; 13: 351357.