Impact of smoking behaviors on asthma incidence and allcause mortality in middle-aged and older adults: A longitudinal study from China.

The impact of smoking behaviors on asthma incidence and all-cause mortality among middle-aged and older adults remains understudied. In particular, whether the potential effect of adolescent smoking initiation on late-onset asthma is independent of cumulative tobacco exposure is unclear. Cox proportional hazards models assessed longitudinal impact of smoking behaviors on asthma incidence and mortality risks using 2011-2018 China Health and Retirement Longitudinal Study (CHARLS) data. Cross-sectional smoking-asthma associations were analyzed with logistic regression. Additionally, restricted cubic splines were used to assess the nonlinear relationships between smoking characteristics and asthma incidence. Smokers had a 65% higher risk of incident asthma compared to non-smokers in middle-aged and older adults (HR=1.65; 95% CI: 1.10-2.46, p=0.015). According to stratified analysis, individuals with smoking duration ≥40 years (HR=1.95; 95% CI: 1.2-3.15, p=0.007), cumulative pack-years under 15 pack-years (HR=1.76; 95% CI: 1.04-2.99, p=0.035), and smoking onset before the age of 18 years (HR=2.31; 95% CI: 1.35-3.96, p=0.002) were at significantly greater risk for asthma. After controlling for cumulative pack-years, early smoking initiation (<18 years) remained an independent and significant predictor of asthma onset in middle and older age (HR=2.56; 95% CI: 1.29-5.06, p=0.007). Subgroup analysis revealed that smoking-related asthma risk was especially elevated among those aged <65 years, females, overweight individuals, and those without baseline comorbidities. Moreover, there was no significant difference in all-cause mortality between the smoking and non-smoking groups in asthma patients. The increased risk of asthma onset among middle-aged and older adults due to adolescent smoking initiation was independent of cumulative smoking pack-years, even though low pack-years and long-term smoking also contribute to increased risk. Targeted smoking cessation programs, especially adolescent prevention, are crucial to reduce asthma burden in this population.