Contributions of obesity and cigarette smoking to incident disability: A longitudinal analysis.

Downward trends in U.S. disability levels are stagnating. Assessing the key contributors to U.S. disability incidence is critical to improving the functional status of the U.S. population. Using longitudinal, nationally representative data from waves 2003-2015 of the Panel Study of Income Dynamics (PSID), we estimated age-specific U.S. disability incidence and quantified the individual and joint contributions of obesity (contemporaneous and earlier-life; BMI ≥ 30) and cigarette smoking to disability incidence. Participants were adults ages 33-96 who participated in PSID in 1986 and at least two consecutive waves 2003-2015 (N = 3247). We conducted age-stratified logistic regressions to predict incident disability at middle and older ages (33-69 years, 70-96 years). Next, counterfactual scenarios were used to estimate the contributions of each risk factor to incident disability. Disability incidence was greater in women than men (5.8 and 4.5 cases per 100 person-years, respectively) and increased with age. Obesity and cigarette smoking jointly explained 17-38% of disability incidence; each factor contributed roughly equal amounts in all groups but older men, for whom smoking history appeared more important. Obesity and smoking appeared to explain more of disability at younger ages (women: 33.1%, 95% CI: 25.1 to 41.0%; men: 37.6%, 95% CI: 28.8 to 46.5%) than at older ages (women: 16.5%, 95% CI: 8.2 to 24.9%; men: 24.5.%, 95% CI: 12.7 to 36.3%). This study provides a benchmark for monitoring trends in U.S. disability incidence. Obesity and smoking are key contributors to disability, accounting for 17-38% of incident disability in U.S. adults.