Association between healthy lifestyle and frailty in adults and mediating role of weight-adjusted waist index: results from NHANES

The relationship between healthy lifestyle and frailty remains unclear. Healthy weight is crucial for overall well-being, but using body mass index (BMI) to evaluate weight management is inefficient. This study clarifies the association between healthy lifestyle or its factors (non-smoking, moderate drinking, healthy weight, healthy diet, sufficeint physical activity, and non-sedentary) and frailty, and the feasibility of using the weight-adjusted waist index (WWI) reflecting central obesity as an intermediate indicator. This study included 4,473 participants from the 2007–2018 National Health and Nutrition Examination Survey (NHANES). Healthy lifestyle quality was assessed by summing the scores of each healthy lifestyle factor. Frailty was assessed using a 49-item frailty index (FI), categorizing participants into robust, pre-frail, and frail. Logistic regression to investigate the association between healthy lifestyle or its factors, WWI, and frailty. Smooth curve fitting and threshold effect analyses were used to elucidate the nonlinear association. Subgroup and two other sensitivity analyses were conducted to confirm the stability of the results. A causal mediation model examined the proportion of frailty mediated by WWI. The study identified 13.98% of the participants as frail. Optimal healthy lifestyle and frailty were negatively associated (OR: 0.39, 95%CI: 0.27–0.58). Five healthy lifestyle factors (non-smoking, healthy weight, healthy diet, sufficient physical activity, and non-sedentary) were associated with a lower prevalence of frailty, with odds ratios (OR) ranging from 0.48 to 0.61. We also analyzed the association between a healthy lifestyle and WWI (OR: 0.32, 95%CI: 0.27–0.37), WWI and frailty (OR: 1.85, 95%CI: 1.59–2.16). A positive association between WWI and FI was observed beyond the inflection point (9.99) (OR: 0.03, 95%CI: 0.02–0.03). Subgroup and sensitivity analyses confirmed stable associations between healthy lifestyle, WWI, and frailty. WWI partially mediated the association between a healthy lifestyle and frailty (mediating ratio = 20.50–20.65%). An optimal healthy lifestyle and positive healthy lifestyle factors are associated with a lower incidence of frailty. WWI may mediate the relationship between a healthy lifestyle and frailty.