Trends in smoking and smokeless tobacco use among Danish Adolescents, 1997-2014

INTRODUCTION: High rates of smoking among adolescents remain a public health concern. This study investigates smoking behavior and use of smokeless tobacco among Danish high-school students and assesses how smoking and use of smokeless tobacco cluster in schools and school classes. We estimate the trend in cigarette smoking from 1997 to 2014. METHODS: We used data on 70 243 students, from 3 214 school classes in 119 high schools, who participated in the Danish National Youth Study from 2014. We had information on 87% of all Danish high schools and 85% of eligible students. We also used data from 1997 on 26 644 high-school students from a similar data set to assess the chronological trend in smoking. We calculated prevalences and intraclass correlation coefficients (ICCs) to estimate between-school and between-school class clustering in smoking and use of smokeless tobacco. RESULTS: In all, 14% of boys and 11% of girls were daily smokers. A large fraction of the variation in smoking and the use of smokeless tobacco was attributable to the school and school-class level (ICC of 0.19, 0.12, 0.16 and 0.27, for daily smoking, waterpipe smoking, use of electronic cigarettes and snuff/chewing tobacco, respectively). Daily smoking decreased from 15% in 1997 to 12% in 2014, while more students were occasional smokers in 2014 than in 1997 (30% vs 18%). CONCLUSIONS: The prevalence of smoking was high among Danish high-school students and had changed little since 1997. The school and class environment accounted for a large part of the variation in smoking behavior.