[Study of association of central obesity and pain with frailty in middle-aged and old people in China].

Objective: To explore the association of central obesity, pain, their joint effect, and interaction with frailty in middle-aged and old people in China. Methods: A total of 14 359 participants aged ≥45 years in 2011, 2013 and 2015 were selected from the China Health and Retirement Longitudinal Study to construct a cohort database. Cox proportional hazards regression models were used to estimate the association of waist-to-height ratio (WHtR) and pain with the risk for frailty. Joint effect and interaction analyses were performed. Results: In the follow-up of 77 783 person-years, frailty developed in 3 198 participants, with an incidence density of 41.11 per 1 000 person-years. Compared with the Q1 level of WHtR, its Q2, Q3 and Q4 level increased risk for frailty by 17% (HR=1.17, 95%CI: 1.05-1.31), 24% (HR=1.24, 95%CI: 1.11-1.40), and 43% (HR=1.43, 95%CI: 1.25-1.63), respectively. Compared with painlessness, suffering from pain increased the risk for frailty by 97% (HR=1.97, 95%CI: 1.83-2.11), and having 1, 2, and ≥3 pain sites increased the risk by 42% (HR=1.42, 95%CI: 1.25-1.61), 86% (HR=1.86, 95%CI: 1.64-2.11), and 138% (HR=2.38, 95%CI: 2.18-2.60), respectively. The results of restricted cubic spline showed that WHtR level was associated with the risk for frailty in a J-type dose-response relationship (total P<0.001, nonlinear P<0.001), and pain quantity was positively associated with the risk in a nonlinear dose-response relationship (total P<0.001, nonlinear P<0.001). Threshold effect analysis revealed that the inflection points of WHtR and pain site number were 0.46 and 2.00, respectively (P<0.001). Joint effect analysis showed that the Q2, Q3 and Q4 levels of WHtR combined with pain increased the risk for frailty by 146% (HR=2.46, 95%CI: 2.11-2.87), 169% (HR=2.69, 95%CI: 2.30-3.16), and 157% (HR=2.57, 95%CI: 2.18-3.03). Conclusions: The risk for frailty increased with the level of WHtR and the number of pain sites in middle-aged and old people, and there was joint effect between WHtR and pain. Comprehensive management and intervention of obesity and pain are significant for the early prevention of frailty.