BIOIMPEDANCE PHASE ANGLE IS INDEPENDENTLY ASSOCIATED WITH THE DEGREE OF FAT DEPOSITION IN MUSCLE: THE SHIZUOKA STUDY

M. Kato^1,2, Y. Okada³, W. Nakano^1,2, D. Takagi^1,2, M. Ochi³, Y. Ohyagi³, M. Igase³, Y. Tabara^2,4

¹Tokoha University, Faculty of Health Science, Shizuoka, Japan, ²Shizuoka Graduate University of Public Health, Graduate School of Public Health, Shizuoka, Japan, ³Ehime University Graduate School of Medicine, Department of Geriatric Medicine and Neurology, Toon, Japan, ⁴Kyoto University Graduate School of Medicine, Center for Genomic Medicine, Kyoto, Japan

Background: Sarcopenia is a composite phenotype of muscle weakness and low physical function. Although loss of muscle mass is a major cause of not only muscle weakness but also physical functional decline, changes in muscle quality i.e., accumulation of fat in the muscle, are also associated with sarcopenia. Phase angle (PhA) has been proposed as a simple marker of muscle quality. This parameter is calculated from the resistance and reactance measured using a bioimpedance device. However, no direct evidence suggests that PhA is independently associated with the degree of fat deposition in muscle (myosteatosis).

Purpose: To clarify the possible association between PhA and myosteatosis in community-dwelling middle-aged to older adults.

Methods: This study population was 424 community-dwelling middle-aged to older individuals (aged ≥ 50 years) who participated in the Shizuoka Study or the Study of Shimanami Health Promoting Program in Japan. PhA and skeletal muscle mass index (SMI) were obtained by bioelectrical impedance analysis. PhA was calculated from the reactance and resistance measured at 50kHz using the following formula: PhA = arctangent (reactance/resistance) × (180/π). The cross-sectional area (CSA) and mean attenuation values (MAV) of the mid-thigh skeletal muscle were calculated from computed tomography images and considered as indexes of skeletal muscle mass and myosteatosis, respectively. A lower MAV indicates greater fat deposition in the muscle because fat has a negative attenuation value. Multiple linear regression analysis was used to identify factors independently associated with PhA and mid‑thigh muscle CSA and MAV.

Results: PhA was inversely associated with age and positively associated with body mass index, SMI, and CSA and MAV at mid-thigh. Multiple linear regression analysis adjusted for covariates identified PhA (β = 0.214, P < .001) and SMI (β = 0.260, P < .001) as independent factors of mid-thigh muscle CSA, while PhA (β = 0.349, P < .001) but not SMI (P = .645) was associated with MAV. The combination of low SMI and low PhA showed stepwise association with cross-sectional area, while only individuals with low PhA had lower mean attenuated value.

Conclusions: PhA obtained by bioimpedance analysis was associated not only with skeletal muscle mass, but also with myosteatosis, a fat deposition in skeletal muscle.

Implications: The findings of this study support the use of PhA as an index of myosteatosis and suggest the importance of the evaluation of PhA in addition to SMI in the assessment of muscle properties.

Funding acknowledgements: This work was supported by the JSPS KAKENHI Grant Number 21H04850 and 22K11190.

Keywords:
Sarcopenia
Phase angle
Myosteatosis

Topics:
Older people
Musculoskeletal
Primary health care

Did this work require ethics approval? Yes

Institution: Kyoto University Graduate School of Medicine

Committee: The Institutional Review Board of Kyoto University Graduate School of Medicine

Ethics number: G1327