Associations between body mass index and peak expiratory flow rate and the mediating role of hand grip strength: evidence from CHARLS.

OBJECTIVE: To investigate the mediating role of Hand Grip Strength (HGS) in the relationship between Body Mass Index (BMI) and Peak Expiratory Flow (PEF) among Chinese middle-aged and elderly adults without diagnosed lung disease. METHOD: This cross-sectional study utilized data from the 2015 China Health and Retirement Longitudinal Study (CHARLS). HGS, BMI, and PEF were assessed through standardized measurements. Logistic regression models were applied to evaluate the associations of BMI and HGS with reduced PEF, defined as PEF%pred < 80%. Mediation analysis was conducted to explore the relation between BMI and PEF%pred via HGS. RESULT: A total of 8784 participants were included in the analysis, with 671 classified as having reduced PEF (PEF%pred < 80%). Higher BMI and greater HGS were each associated with significantly lower odds of reduced PEF (per 1-unit increase in BMI: OR = 0.970, 95% CI: 0.946-0.993; per 1 kg increase in HGS: OR = 0.961, 95% CI: 0.952-0.970), implying that lower BMI and lower HGS are related to increased risk. Mediation analysis indicated that HGS statistically mediated the association between BMI and PEF%pred; however, the absolute indirect effect size was very small (indirect effect = 0.003, 95% CI: 0.003-0.004), corresponding to a negligible change in PEF%pred. CONCLUSION: Both low BMI and reduced grip strength are significantly associated with greater odds of reduced PEF in Chinese middle-aged and elderly adults. Although HGS mediates part of the statistical association between BMI and PEF, the clinical significance is limited due to the small effect size. These results do not support specific muscle-strengthening interventions based on this finding alone, and caution should be exercised in clinical interpretation.