Does smoking in adolescence affect body mass index, waist or height? Findings from a longitudinal study

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Abstract
Aim To assess the effect of smoking uptake on body mass index (BMI), waist circumference and height during adolescence. Design Five‐year longitudinal study. Setting Thirty‐six schools in South London, England, selected by a stratified random sampling procedure designed to ensure ethnic and socio‐economic diversity. Participants A total of 5863 students took part in the HABITS (Health and Behaviour in Teenagers) Study between 1999 and 2003. Measurements Self‐reported smoking behaviour, saliva cotinine concentrations and measured weight, waist circumference and height were obtained, along with information on gender, ethnicity, socio‐economic deprivation, pubertal status, self‐reported exercise and dieting. Students were examined annually from school year 7 (ages 11–12) to year 11 (ages 15–16), with response rates ranging from 74 to 84%. A total of 2665 never smokers at year 7 with complete data for years 7 and 11 were included in the analyses. Findings Adjusting for year 7 BMI and other potential confounders, regular smokers (more than six cigarettes a week) at year 11 had significantly lower BMI (P = 0.002) than other students. Smokers defined by a cotinine above 15 ng/ml also had lower BMI (P < 0.0001). Waist circumferences were lower in regular smokers (P = 0.014) and cotinine‐defined smokers (P < 0.011). No consistent association was found between smoking and height. The adjusted difference in weight between regular smokers and other students amounted to 1.8 kg (95% CI, 0.52–3.17) for an average‐height student. Conclusion Taking up regular smoking during adolescence may result in a lower BMI, but the effect is small and of uncertain significance.