Masseter Muscle Volume and Its Association with Sarcopenia and Muscle Determinants in Older Japanese Adults: the Bunkyo Health Study

Sarcopenia has been with a decrease in masseter muscle (MM) thickness in high-risk older populations. However, the relationship between sarcopenia and determinants of MM volume (MMV) in the general elderly population remains unclear. In a cross-sectional study of 1,484 older adults in Tokyo, we evaluated MMV using 3D MRI scanning, appendicular skeletal muscle mass (ASMM), handgrip strength, dietary intake, smoking, insulin-like growth factor 1 (IGF-1) levels, and the ACTN3 R577X polymorphism. Participants were divided into quintiles based on MMV (Q1–5). Participants in our study had a mean age of 73.0 ± 5.3 years and their MMV (Men: 35.3 ± 7.8 mL, Women: 25.0 ± 5.1 mL) was significantly higher in men than in women. A significant association between MMV and sarcopenia was observed, with the lowest quintile (Q1) showing a higher risk compared to the highest quintile (Q5) in both sexes. Body mass index (BMI) and age were independent determinants of ASMM in both sexes, whereas BMI, but interestingly not age, was a determinant of MMV. Moreover, IGF-1 was positively correlated with MMV in both sexes; smoking was negatively correlated with MMV in women. The ACTN3 577XX genotype was only associated with smaller MMV in men. Low MMV increased the risk of sarcopenia, particularly in men. BMI and age strongly influenced ASMM, while MMV was only weakly associated with BMI and not with age. Notably, IGF-1 level was positively associated with MMV only, and ACTN3 genotype was associated to reduced MMV only in men.