Assessing 30-day quantity-frequency of U.S. adolescent cigarette smoking as a predictor of adult smoking 14 years later

Background: To improve measures of monthly tobacco cigarette smoking among non-daily smokers, predictive of future non-daily monthly and daily smoking. Methods: Data from United States National Longitudinal Study of Adolescent to Adult Health, tracking adolescents, ages 12-21, over 14 years were analyzed. At baseline, 6501 adolescents were assessed; 5114 individuals provided data at waves 1 and 4. Baseline past 30-day non-daily smokers were classified using quantity-frequency measures: cigarettes smoked/day by number of days smoked in the past 30 days. Results: Three categories of past 30-day non-daily smokers emerged using cigarettes/month (low:1-5, moderate: 6-60, high: 61+) and predicted past 30-day smoking at follow-up (low: 44.5%, moderate: 60.0%, high: 77.0%, versus 74.2% daily smokers; r_τ= -0.2319, p < 0.001). Two categories of non-smokers plus low, moderate and high categories of non-daily smokers made up a five-category non-daily smoking index (NDSI). High NDSI (61+ cigs/mo.) and daily smokers were equally likely to be smoking 14 years later (High NDSI OR = 0.97, 95% CI = 0.53-1.80 [daily as reference]). Low (1-5 cigs/mo.) and moderate (6-60 cigs/mo.) NDSI were distinctly different from high NDSI, but similar to one another (OR = 0.21, 95% CI = 0.15-0.29 and OR = 0.22, 95% CI = 0.14-0.34, respectively) when estimating future monthly smoking. Among those smoking at both waves, wave 1 non-daily smokers, overall, were less likely than wave 1 daily smokers to be smoking daily 14 years later. Conclusions: Non-daily smokers smoking over three packs/month were as likely as daily smokers to be smoking 14-years later. Lower levels of non-daily smoking (at ages 12-21) predicted lower likelihood of future monthly smoking. In terms of surveillance and cessation interventions, high NDSI smokers might be treated similar to daily smokers.