Plasma superoxide dismutase activity in relation to disability in activities of daily living and objective physical functioning among Chinese older adults

Background: This study aimed to examine the associations of plasma superoxide dismutase (SOD) activity, an indicator of oxidative stress, with disability in activities of daily living (ADL) and objective physical functioning among Chinese older adults. Methods: We used cross-sectional data of 2223 older adults (>= 65 years, including 1505 adults >= 80 years) from the 2011/2012 main survey of the Chinese Longitudinal Healthy Longevity Survey (CLHLS) and the 2012 biomarker sub-study. Plasma SOD activity was assessed by the T-SOD assay kit based on the hydroxylamine method. Outcomes included ADL disability and disability in three objective physical tasks (standing up from a chair, picking up a book from the floor, and turning around 360 degrees). Logistic regression models were used to examine the associations of plasma SOD activity with outcomes. Results: After controlling for age and sex, compared with participants in the lowest quartile group of SOD activity, those in the highest quartile group had 31% lower odds of ADL disability (odds ratio [OR]: 0.69; 95%CI: 0.48, 0.98); 60% lower odds of disability in standing up from a chair (OR: 0.40; 95%CI: 0.25, 0.63); and 57% lower odds of disability in picking up a book from a floor (OR: 0.43; 95%CI: 0.28, 0.65). The results did not change substantially after controlling for additional covariates. We did not observe statistically significant age and sex differences. Conclusions: Overall, plasma SOD activity was associated with subjectively and objectively measured disability in Chinese older adults, highlighting the potential of SOD activity to serve as a biomarker of physical functioning.