Gender-dependent association of body mass index and waist circumference with disability in the Chinese oldest old.

OBJECTIVES: To explore associations of BMI and waist circumference (WC) with disability among the Chinese oldest old. METHODS: The 5,495 oldest old in the sixth wave of Chinese Longitudinal Healthy Longevity Study conducted in 2011 were included in this study. Disability was assessed by activities of daily living (ADL); height and weight for BMI and WC were measured; information including socio-demographics, lifestyles, and health status was collected. RESULTS: Generalized additive models analysis showed that the association of BMI/WC with ADL disability was nonlinear. Among the males, logistic regression results supported a "J" shape association between ADL disability with BMI/WC-the highest tertile group in BMI or WC was significantly associated with an increased risk of ADL disability: odds ratio 1.78 (95% confidence interval (CI): 1.26-2.52) for BMI and 2.01 (95% CI: 1.44-2.82) for WC. Among females, an inverse "J" shape association was found, only the lowest tertile group before the cutoff point had an increased risk of ADL disability: odds ratio 1.42 (95%CI: 1.02-1.97) for BMI and 1.47 (95% CI:1.06-2.04) for WC. CONCLUSIONS: Associations of BMI and WC with ADL disability are significant even in the oldest old, but differ between the genders.