Recent research published in the Journal of Adolescent Health investigated the relationship between smoking trajectories beginning is adolescence and adult weight status. The results suggest that smoking does not mitigate the risk of developing obesity.
Cigarette smoking and obesity are two of the main causes of disease and premature death in the United States. While smoking harms nearly every organ of the body and is correlated with both cancer and cardiovascular disease, type 2 diabetes rates have been steadily increasing along with childhood obesity. Studies show that cigarette smoking is commonly initiated in adolescence, as with the development of the primary health behaviors related to obesity, such as physical activity levels and food preference. Consequently, adolescence is a crucial period due to the increased probability that such health behaviors established during this time may be carried over in adulthood. Needless to say, both smoking and obesity are important health issues that affect adolescents and accordingly merit awareness and intervention early on to prevent negative outcomes later in life.
While there exists a growing body of literature that has already addressed the relationship between smoking and obesity among adolescents and young adults, the results have been mixed. However, a study recently published in the Journal of Adolescent Health attempts to provide more conclusive answers, combining the reliability of a large, nationally representative sample with the temporal accuracy of a longitudinal study. In all, the researchers concluded that while people with smoking histories had slightly lower body mass indices (BMI) and waist circumferences compared to non-smokers, an increased population-level BMI was observed in all groups over time—concluding that smoking does not magically protect against obesity.
The National Longitudinal Study of Adolescent to Adult Health (Add Health) was the largest and most comprehensive longitudinal study of adolescents into young adulthood in the United States. Data collection was split up temporally in the following manner: Wave I participants were in grades 7-12 (1995-1996), with subsequent follow-up in 1996 (Wave II), 2001-2002 (Wave III), and 2007-2008 (Wave IV). In order to be adequately representative of all U.S. schools, Add Health collected data from 80 high schools and 52 middle schools across the country. The impressive final study sample of 13,361 provided the data used for the paper. During Waves I and II, participants were asked their age at the time of their first cigarette, with the age of 14 being the threshold for classification as either an early or late initiator. At all waves, participants were queried on their current cigarette smoking status. To characterize patterns of smoking across the life course, a series of analyses were conducted, taking into consideration current cigarette smoking status at all four waves, along with age of initiation, to produce four trajectories of cigarette use; these classes were labeled as early establishers, late establishers, former smokers and non-smokers. The main outcome of BMI at Wave IV was calculated for each participant using self-reported values of weight and height. Because the subjective nature of self-reported values can be seen as a limitation in the study, each participant’s waist circumference was additionally measured by interviewers to provide a secondary measure of weight status. After adjusting for participants’ initial weight status in adolescence, statistical analyses were performed to assess the relationship between smoking trajectory and BMI at Wave IV.
The main finding from these analyses was that by Wave IV, all participants who were current or former smokers had a statistically significant lower BMI than non-smokers. That is not to say, however, that we should all start smoking to lose weight: it was also found that for all trajectories—early establishers, late establishers, former smokers and non-smokers alike—mean BMI increased over time from Waves I to IV. In other words, although individuals with smoking histories showed slightly lower BMIs and waist circumferences than non-smokers, the mean BMI for each group was well above the threshold for being overweight; thus, the negligible differences in BMI between trajectories were unlikely to produce any tangible health benefits, especially given any smoking history. These findings are not only consistent with previous research, but also with national secular trends in obesity.
All in all, this study builds on previous literature by characterizing the relationship between cigarette smoking trajectories and weight status from adolescence to young adulthood. More importantly, it indicates the need for further concurrent studies on smoking and obesity in order to better understand potential additive and/or synergistic effects among adolescents and young adults in the United States. In the time that it may take for such studies to materialize, it seems there is one thing that can be done now in order to reduce negative public health outcomes in the not-so-distant future: instill in adolescents the proper health behaviors to avoid smoking and weight gain altogether in adulthood.
Written By: Rebecca Yu