Characteristics and consistency of light smoking: Long-term follow-up among Finnish adults

The main body of smoking behavior research has targeted primarily moderate and heavy smoking. This study aimed to define characteristics of daily light smoking and to examine the consistency of this smoking pattern. We examined light smoking among the Finnish adult population using longitudinal data from the Older Finnish Twin Cohort, collected in 1975, 1981, and 1990. We defined light smoking as fewer than 5 cigarettes/day and heavy smoking as 20 or more cigarettes per day. We examined the characteristics of light smokers in comparison to heavy smokers, studied which baseline features predicted change in the light smoking pattern, and described how this pattern changed over time. Among 9,940 current smokers in 1975, we identified 772 (7.8%) light smokers and 2,668 (26.9%) heavy smokers. Cross-sectionally, light smoking was characterized by female sex; younger age; higher education; lower consumption of alcohol, coffee, and other tobacco products; being single and physically active; and older age at smoking onset. Light smokers reported strong inhalation of cigarette smoke less often than did other smokers. Longitudinally, higher education, binge drinking, and moving in with a partner predicted changes in light smoking. The majority of the baseline light smokers were former, moderate, or heavy smokers at follow-ups, whereas only about 6% reported consistent light smoking throughout the 15-year study period. In long-term follow-up, consistent light smokers represent a relatively small fraction of smokers. This dynamic pattern of light smoking complicates inferences from studies of health consequences, suggesting that light smoking should not be evaluated based on a single assessment.