The importance of age of smoking debut and packyears on development of respiratory symptoms and asthma in young adulthood

<bold>Aim:</bold> to prospectively study age of smoking debut and packyears in relation to respiratory symptoms and asthma at age 28 years. Method: The Obstructive Lung Disease in Northern Sweden (OLIN) studies recruited a cohort of 8-year-old children in 1996 (n=3430; 97% of invited). The cohort was followed annually until age 19y, by questionnaire surveys about asthma, respiratory symptoms, and from 13y, smoking habits. Additionally, the cohort was followed-up by postal questionnaire at age 28y (n=2291; 71% of invited). <bold>Results:</bold> Being a daily smoker was reported at least once by 22%, more commonly by women than men, 25 vs. 19%, p<0,001. Of ever smokers, 29% started smoking ≤15y (mean packyear 2.3), 35% between 16 and 17y (py 1.8), and 35% ≥18y (py 1.2). Among all 2291 participants at age 28y, 23% reported asthma and 53% reported any respiratory symptom, the most common were any wheeze last 12 months (36%) and sputum production (30%). After adjustment for sex, family history of asthma, exposure to smoking in childhood and educational level, any respiratory symptom was associated with packyears (OR1.1 95%CI 1.0-1.2) and smoking debut age ≤15 years (OR1.8; 1.2-2.7), 16-17y (OR1.8; 1.3-2.6), and ≥18y (OR1.5; 1.1-2.1), compared with never smokers. Smoking debut ≤15y (OR1.7; 1.2-2.6) and packyears (OR1.1; 1.0-1.2) was associated with asthma in unadjusted analyses, but not in the adjusted analyses. <bold>Conclusion:</bold> The majority of smokers started smoking at age <18 years, and early smoking debut and higher number of packyears was associated with respiratory symptoms already at age 28 years, despite low number of packyears.