Impact of demographic and lifestyle factors on the association between body mass index and the presence of sarcopenia at follow-up in community-dwelling people aged 40-74 years: a 9-year follow-up study

Abstract Objective: Although body mass index (BMI) is associated with sarcopenia, factors that modify this association are unclear. This study aimed to clarify how demographic and lifestyle factors affect the association between BMI and sarcopenia in older adults. Design: A 9-year follow-up study. Setting: Community-based cohort in Japan. Participants: A total of 6,632 individuals aged 40–74 years participated in this study. BMI, demographic and lifestyle factors, and disease history were assessed in a baseline survey conducted between 2011 and 2014. Sarcopenia was not assessed at baseline. Sarcopenia status was assessed based on the diagnostic criteria of the Asian Working Group for Sarcopenia 2019 during follow-up examinations conducted in 2021 and 2022. The odds ratio (OR) for the presence of sarcopenia at follow-up was calculated using multivariable logistic regression analysis. Results: A lower BMI was associated with a higher odds of sarcopenia in both males and females (P for trend <0.0001). Significant interactions were observed between BMI and age (P for interaction=0.0003), and between BMI and physical activity level (P for interaction=0.0264), in sarcopenia. Specifically, the odds of sarcopenia among underweight individuals (<18.5 kg/m 2 ) was significantly higher than that of their counterparts in the subgroup aged <68 years and in the subgroup with high total physical activity (≥40.1 MET-hr/d). Conclusions: Low BMI is strongly associated with sarcopenia, and this relationship is modified by age and physical activity level. Specifically, the adverse impact of being underweight on sarcopenia was greater among middle-aged individuals and those with high physical activity levels.