INTRODUCTION

Tobacco use is the largest preventable cause of death globally, and is responsible for more than 8 million deaths per year¹. Most developed countries have recorded a decreasing prevalence of tobacco smoking; however, the prevalence has been increasing in low- and middle-income countries, particularly Sub-Saharan Africa, partly due to cigarette affordability and aggressive marketing by tobacco companies². In Nigeria, about 16100 tobacco-related deaths occur annually³. It is likely that these numbers may be grossly underestimated because of weak surveillance systems. In addition, 5.6% (4.7 million) of Nigerian adults currently use a tobacco product and 3.9% (3.1 million) adults are current tobacco smokers⁴. Of greater concern is tobacco smoking by children and adolescents where 25000 Nigerian children (aged 10–14 years) smoke cigarettes each day³. Cigarettes are affordable for young people in Nigeria because they are still being sold in single sticks, despite the provision of Article 16 of the Framework Convention on Tobacco Control to which Nigeria is a signatory⁵. The dangers of tobacco smoking from an early age are well established and include diseases of the heart, respiratory system, central nervous system and cancers of almost all organs of the body. There is also an increased risk of addiction to nicotine. The dangerous effects of tobacco smoking on the developing brains of children and adolescents⁶ are of great concern, necessitating more effective tobacco control globally.

Several factors have been shown to influence tobacco smoking by adolescents^7-13. These include sociodemographic, environmental, and psychosocial factors. A recent systematic review of studies on adolescent tobacco smoking in Nigeria showed peer smoking, parental smoking, media advertisements, male gender, increasing age, low parental education, and family conditions as significant determinants of tobacco smoking¹⁴. Most of these studies were school-based, yet none investigated the association between school geographical location or socioeconomic status (SES) and adolescent tobacco smoking. These are important contextual factors that have been shown to influence adolescent tobacco use^7-13. Understanding the association between these contextual factors and adolescent tobacco smoking is necessary for developing effective smoking prevention and cessation interventions. Moreover, it is likely that tobacco smoking could vary between schools but this has not been investigated in other studies in Nigeria.

The objectives of this study were to determine the factors associated with adolescent tobacco smoking in Nigeria and investigate the interaction between school location and socioeconomic status (SES). To the best of our knowledge, this is the first study to investigate determinants of adolescent tobacco smoking in Nigeria using multilevel analysis.

METHODS

Statistical analyses

Data were analyzed using Stata Version 11. We computed weighted prevalence estimates and 95% confidence intervals for each type of tobacco smoking. Multilevel mixed effects logistic regression models were used to determine predictors of each outcome – current cigarette smoking and current smoking of other tobacco product. We started with a 2-level null model that contained each of the outcomes with students nested within schools and a random intercept at school level, assuming covariance ‘identity’ structure, the default method used when only one variable is specified in the random part of the model. Each covariate was then added to the fixed part of the model while maintaining random intercept at school level. The covariates examined included sociodemographic characteristics, school characteristics, and environmental factors. Covariates that reached statistical significance of ≤0.2 in the bivariable analyses and those specified a priori were included in the multivariable model with random intercept at school level using forward selection¹⁷. A conceptual framework (Figure 1) guided the multivariable analysis.

Figure 1

Conceptual framework showing factors influencing adolescent tobacco use

We examined if the odds of smoking varied by geographical location by introducing random coefficient at location. Likelihood ratio test comparing models with and without random coefficient was in favor of the simpler model without random coefficient at location. To test whether SES modified the smoking–school location association, an interaction term between school location and SES was introduced in the multivariable models. A separate model was developed for fathers’ SES and mothers’ SES.

Each of the models with the interaction term was compared to the model without the interaction term using a likelihood ratio test. Mothers’ SES showed no association with adolescent smoking, so models with fathers’ SES were used. There was no evidence of interaction in the model for current smoking of other tobacco products. The final model for predicting current cigarette smoking did not include students’ grade, students’ status, and school type. Similarly, grade, students’ status and inclusion of tobacco in school curriculum were not included in the final model for predicting current smoking of other tobacco. We considered p<0.05 as statistically significant and restricted analyses to adolescents.

RESULTS

There were 4332 adolescents out of 4354 respondents, with 2230 and 2102 students from urban and rural schools, respectively. Response rates were 84.4% in urban and 80.6% in rural locations. Students in urban schools were younger, more of the parents were employed and lived together, and had a higher proportion of parents with high SES (Table 1). Reported prevalence of current smoking of cigarettes

and other smoked tobacco were 13.3% (95% CI: 11.3–smoking. Females were less likely to be current 15.7) and 5.8% (95% CI: 4.6–7.2), respectively.

Table 2 shows predictors of current cigarette smoking. Females were less likely to be current smokers of cigarettes (OR=0.73; 95% CI: 0.59–0.91). Possession of weekly spending money of more than 100 NGN (about 0.27 US$) increased the odds of cigarette smoking by 1.7 (95% CI: 1.29–2.17). There was a reduction in odds of cigarette smoking when parents were employed, with 42% reduction in odds when both parents were employed. Students who were exposed to secondhand smoke (OR=2.01; 95% CI: 1.59–2.54) or to tobacco advertisements (OR=1.39; 95% CI: 1.07–1.80) had higher odds of smoking cigarettes. Inclusion of tobacco in school curriculum reduced the odds in cigarette smoking by 41%. There was a graded increase in odds of cigarette smoking as the number of parent smokers or peer smokers increased, with friends’ smoking having the greatest effect (if ‘all’ of friends smoked). Students who could buy cigarettes near their school had 1.8 times higher odds of being current smokers.

A significant interaction was found between school location and father’s SES for cigarette smoking odds (OR for interaction term=1.86; 95% CI: 1.17–2.94; cigarette smokers (OR for interaction term=1.86; 95% CI: 1.17–2.94; p=0.008) (Table 2). Stratum-specific odds ratios for school location and father’s SES are presented in Table 3 as recommended by Knol et al.¹⁸. Compared to students of low SES in urban schools, students of high SES in rural schools had higher odds of being current cigarette smokers (OR=1.75; 95% CI: 1.14–2.69). The odds of current smoking in rural compared to urban schools were much higher for students of high SES compared to students of low SES (2.28 vs 1.23). Conversely, in urban schools, students of high SES had lower odds of being current smokers although not statistically significant (OR=0.77; 95% CI: 0.55–1.06) while in rural schools, high SES increased the odds of smoking (OR=1.42; 95% CI: 1.03–1.96).

Predictors of current smoking of other tobacco products are shown in Table 4. Students who attended rural schools (vs urban), had weekly spending money >100 NGN (vs none), were exposed to secondhand smoke or pro-tobacco advertisements, had smoking parents (both smoked), friends (some, most, or all) or classmates (all) or could buy cigarettes near school, were more likely to be current smokers of other tobacco products. Conversely, older students (vs 10–12 years age group), female students (vs males), and students of high SES (vs low SES) were less likely to be current smokers of other tobacco products. There was no evidence of interaction between school location and fathers’ SES (p=0.22).

The odds of both current cigarette smoking and current smoking of other tobacco products differed by school (p<0.001). Addition of sociodemographic, school-level and environmental factors to the null models reduced the variance in current cigarette smoking by 36.8% and current smoking of other tobacco by 38.1%. After adjusting for sociodemographic, school-level and environmental factors, 6.4% of the odds of current cigarette smoking and 8.9% of the odds of current smoking of other tobacco were explained by differences between schools.

DISCUSSION

This study has five main findings. First, attending rural schools was significantly associated with increased odds of current smoking of cigarettes among students of fathers with high SES but not students of fathers with low SES. Second, attending rural schools was significantly associated with increased odds of current smoking of other tobacco products. Third, the association between fathers’ SES and current smoking of cigarettes differed by school location. In rural schools, students with high fathers’ SES were more likely to be current smokers but in urban schools, there was no association between father’s SES and current smoking. Fourth, environmental factors associated with current smoking of cigarettes and other smoked tobacco were similar, and included exposure to secondhand smoke and tobacco advertisements, having smoking peers or parents, and sale of cigarettes near schools. Being taught about tobacco in school predicted lower odds of smoking cigarettes but not smoking other tobacco products. Fifth, students of fathers with high SES were less likely to smoke other tobacco products compared to students of fathers with low SES.

The finding that a positive association between schooling in a rural area and adolescent cigarette smoking was much higher among high SES compared with low SES groups supports our proposition at the beginning of the study that the association between school location and adolescent tobacco use may be different at different levels of SES. It also suggests that students of high SES group are more vulnerable to cigarette smoking in rural compared to urban schools. Similar association was reported in a Scottish study although the result was not statistically significant perhaps due to reduced power caused by the introduction of many interaction parameters¹⁹. We also found that high SES was positively associated with cigarette smoking in rural schools but not in urban schools. These findings have important implications for tobacco control in Nigeria since the target populations for adolescent tobacco control programs may need to be different in different locations. Students with high parental SES need to be targeted in rural locations contrary to previous findings that low SES groups are at higher risk of tobacco smoking^10,11.

Increased risk of tobacco smoking in rural compared to urban schools is consistent with findings from previous studies mostly in developed countries^7-9,20,21. Possible contributory factors are higher exposure of students in urban schools to anti-tobacco messages and to tobacco teaching in school in this study. Increased knowledge about tobacco has been shown to reduce risk of adolescent smoking²². Conversely, Enugu State is not known for tobacco farming, so this may not explain the urban–rural differences in tobacco smoking in this study. Our finding that male students were more likely to smoke is consistent with previous studies in Nigeria and other countries^23-28. Contrary to previous studies^29-31, we found that tobacco smoking decreased with increasing age. A possible explanation is that these younger students were in the experimental phase of using tobacco. It could also be a pointer to the tobacco epidemic that is facing developing countries. Similar results were reported in rural Zambia³² and highlights the need for smoking prevention interventions that target younger students. The finding of increased odds of current smoking with increasing monetary allowance has been reported previously³³; it suggests that it may be necessary to discourage monetary allowance to adolescents.

Several environmental factors were found to be associated with both types of tobacco smoking. Most notable were the influence of parental and peer smoking. Students who reported that all their friends or classmates smoked had 7 times and 4.5 times higher odds, respectively, of being current smokers of cigarettes compared to those with nonsmoking friends or classmates. Similar findings were reported in Iraq³⁴. These observations could be due to peer selection whereby adolescent smokers tend to befriend other smokers. Another explanation could be that adolescent non-smokers tend to initiate smoking when they have smoking friends. The magnitude of the association was less with classmates’ smoking. These findings suggest the strong role of peer influence on adolescent tobacco smoking in this setting. Although it has been reported that adolescent smokers were likely to overestimate the smoking status of their friends³⁵, this may not explain the finding in this study considering the magnitude of the association observed with peer smoking.

The finding that adolescents’ friends and classmates were significant predictors of tobacco use in this study makes it imperative that policymakers develop policies that decrease the ease with which young people obtain and supply tobacco. Possible strategies could include limiting the number of tobacco outlets, particularly around schools, and enforcing consistent and larger excise tax increases, making it harder for adolescents to afford, access, and supply tobacco. Similarly, the finding that students who had both smoking parents were twice as likely to currently smoke tobacco demonstrates the strong influence parents’ lifestyle has on their children, knowledge of which can be harnessed in adolescent tobacco control programs. Smoking prevention programs therefore need components focused on parents to help reduce adolescent smoking.

Despite the ban on pro-tobacco advertising in Nigeria³⁶, a significant proportion of students (73%) in this study were exposed to some form of pro-tobacco advertisement in the past 30 days. Consequently, students who were exposed to pro-tobacco advertisements had increased odds of being current smokers. This finding emphasizes the need for more comprehensive bans on tobacco advertisements to minors. As legislations are not strictly enforced in Nigeria, implementation of plain packaging as part of a comprehensive approach to tobacco control could be worthwhile³⁷. Similar findings were reported for the African region following a secondary analysis of the GYTS of 20 low- and middle-income countries³⁸. Our finding that exposure to secondhand smoke in the past 7 days increased the likelihood that adolescents are current smokers is consistent with previous evidence³¹. These findings suggest that adolescents may perceive smoking as socially acceptable when they are consistently exposed to the behavior in their environment. In general, denormalization campaigns that reduce the attractiveness and accessibility of tobacco could decrease the social acceptability of smoking and make adolescents less likely to use tobacco. These denormalization strategies have been found to have population-wide effects that influence adolescents^39,40. It is, therefore, critical that policy makers key into these strategies in Nigeria.

Students who could buy cigarettes near their school were markedly more likely to be current smokers compared with those who could not. This compares with findings in California and Canada, which showed higher prevalence of current smoking at schools located in neighborhoods with high tobacco outlet density compared to those without any tobacco outlets^41,42. This finding presents the need for policy restricting tobacco sale around schools in Nigeria. We found that inclusion of tobacco in the school curriculum reduced the odds of current smoking of cigarettes by 43%, suggesting that this method of delivery of anti-tobacco messages may be effective. Similar findings were reported in a secondary analysis of GYTS in four South Asian countries²².

CONCLUSIONS

We found an association between school location and current adolescent cigarette smoking that differed by socioeconomic status. This study also established that adolescent smoking of tobacco products other than cigarettes was higher in rural schools and among students of low SES. Our findings have demonstrated that exposure to secondhand smoke and tobacco advertisements, parental and peer smoking, and sale of tobacco around schools, were positively associated with adolescent tobacco smoking. Policy interventions to restrict access to tobacco products around schools, comprehensive bans on tobacco advertisements and sale to minors, in addition to behavioral and other context-specific and culturally adapted interventions are needed to bend the curve of increasing tobacco smoking in Sub-Saharan Africa. Further research is needed to better understand these country-specific interactions between geographical location, socioeconomic status and adolescent tobacco smoking.