The association of hemopexin, muscle quality, and sarcopenia in Japanese older adults with cognitive impairment: a cross-sectional study

Objective: To examine the cross-sectional associations of hemopexin, muscle quality, and sarcopenia status with cognitive function among older Japanese adults with cognitive impairment, and to explore the potential sex-specific differences. Methods: A total of 580 older adults (372 women, 208 men; mean age 83.3 ± 6.2 years) who presented with cognitive impairment at the Kyoto Dementia Comprehensive Center between 2018 and 2022 were enrolled. Cognitive function was assessed using the Mini-Mental State Examination (MMSE). Hemopexin level was measured by enzyme-linked immunosorbent assay. Muscle quality was evaluated via phase angle (PhA) and grip strength, and sarcopenia status was defined using the Asian Working Group for Sarcopenia criteria. Multiple linear regression models, including sex-stratified analyses, were conducted to determine the relationships of these variables with MMSE scores. Results: Higher hemopexin levels (β = 1.19, p = 0.017), PhA (β = 0.59, p = 0.005), and grip strength (β = 0.14, p < 0.001) were independently associated with better MMSE scores, whereas sarcopenia was negatively linked to MMSE scores (β = − 2.28, p < 0.001). Notably, sex-stratified models indicated that hemopexin positively predicted MMSE scores in men but not in women; meanwhile, sarcopenia showed a stronger negative impact in women. Educational attainment also displayed a significant positive association with cognitive performance in both sexes. Conclusions: In this cross-sectional study of older Japanese adults with cognitive impairment, hemopexin levels and muscle quality emerged as important correlates of cognitive function, particularly in men, while sarcopenia was negatively linked to cognition.