Factors Affecting Cigarette Smoking in Adolescents: A Systematic Review

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cancer and chronic heart and pulmonary diseases (13). Adolescent cigarette smokers are faced with a higher risk of diseases and mortalities (14). Half of the adolescent smokers become ordinary smokers in adulthood, and as expected, the other half of the population die due to diseases associated with cigarette smoking. This would further highlight the irreparable consequences of smoking cigarettes among the youth and the need to eliminate this habit (15). Therefore, a sound knowledge of factors correlating with smoking cigarettes can help policymakers and specialists to take effective cultural and supportive measures to reduce the rate of smoking in general and smoking among adolescents in particular. So far, many studies have addressed factors affecting cigarette smoking among adolescents (13,(16)(17)(18)(19)(20). Given the growing interest in cigarette smoking behavior among adolescents, the limited studies among the related literature on factors affecting cigarette smoking behavior by adolescents, and the importance of health in adolescents, this study was an attempt to cover the gap in the field of the study. It aimed to investigate the complex interrelationship between and among factors at several levels (e.g., personal, social, and environmental) and develop preventive general health programs and particular interventions for adolescents.

Methods
In this systematic review, the stages of the search for literature, selection of studies, data extraction, and methodological quality assessment of studies were as follows:

Literature Search and Review
Seven international scientific databases and two Iranian scientific databases, including Google Scholar, EBSCOhost, Proquest, Scopus, ScienceDirect, Web of Science, PubMed, Scientific Information Database (SID) (Iranian database), and IranMedex (Iranian database) were searched from January 2005 to July 2022. These databases were comprehensive in content and contained the most relevant academic papers.

Search Strategy
To find articles on cigarette smoking among adolescents, a search strategy was made by following keywords with Boolean operators: adolescence OR young adult OR youth OR teenagers OR boys OR girls OR children AND uptake AND factors affecting smoking AND adolescent smoking. The operating key AND was used in the search to find more relevant results, and OR was used to extend the search and include keywords similar to the search.

Primary Outcomes
The prevalence of smoking and factors related to smoking in adults were the main outcomes of the study. The present study used the definition by the WHO (18) for adolescence as the age between 10 and 19 years.

Inclusion and Exclusion Criteria
The inclusion criteria were access to full-text, Persian or English language to ensure the absence of any bias in translation, only scientific research since they have already met the necessary conditions of scientific approach, and publication between 2005-2022 to make sure of the recency of content, and focusing on adolescents aged between 10-19 years.
The search process was done independently by three researchers. In cases where the search results of two researchers did not agree, the search of a third researcher was used. No limit was set in terms of the type of participants and place of the study. A manual search was done among journals, books of abstracts in conferences, conventions, and dissertations. The process of selecting the papers involved an initial manual search of the relevant journals and abstracts of conferences, conventions, and dissertations by two independent authors. Next, the recurrent papers were eliminated. The next step was to further limit the search so that irrelevant results could be discarded. After a review of abstracts and titles of all papers and considering the inclusion criteria, potential papers for inclusion were selected. The full text of the target papers was reviewed by two authors and discussed until consensus was achieved.
As for data extraction, the specific features of each paper were extracted using a standard form developed by the present researchers. This form included such information as the title (of paper), authors' names, place of study, year of study, the purpose of study, type of study, target population, sample size, and the main findings.

Methodological Quality Assessment
To critically evaluate the quality of papers, the Joanna Briggs Institute checklist was used, which measures the specificity and applicability of each study in 8 dimensions. The 8 dimensions included the clarity of the inclusion and exclusion criteria of the study, the clarity of the statistical population, the adequacy of the sample size, the reliable and valid instrument, the clarity of the purpose of the study, the clarity of confounding factors, the precise statement of method, and appropriate analysis and interpretation.

Discussion
The present study aimed to explore the effective factors in cigarette smoking among adolescents. The body of reviewed research varied in terms of research methodology, target variables, measurement instruments, and target population. This can make the direct cross-comparison of these studies demanding. Despite this challenge, a systematic review could provide comprehensive information about different factors affecting cigarette smoking among adolescents.
In their meta-analysis study in 2020, Ehsani-Chimeh et al showed that the presence of a smoker in the family, lack of awareness of the consequences of smoking, easy access to cigarettes, lack of government laws to sell it to adolescents, death of family members, parents, gender, having smoking friends, family dissatisfaction, highly emotional environment, divorce, family disputes, history of running away from school and home, curiosity about the experience of smoking, social problems, low education level of parents, and low economic level of the family were determinants of smoking behavior in adolescences (8). As can be observed, these findings are consistent with the individual, family, psychological, and social factors obtained in the present study. In line with the present study, in a systematic review study in 2020, Alotaibi et al found that individual factors (e.g., older age, male gender, unemployment, high income, low awareness, being single, and stress), social factors (e.g., smoking friends, teachers, and parents, parents' education, and parents' occupation), and environmental factors (e.g., media and laws) are among the factors influencing adolescent smoking (77). In a systematic review study in 2016, Talip et al found that individuals who are more prone to smoking are older male adolescents who have parents with low socioeconomic status and low level of education, individuals with low parental supervision and with high-risk behaviors for health, and those who have no conversation about smoking at home (78).
Further, the findings of a study by Wang et al in 2016 indicated that the factors influencing smoking in older adolescents were being a boy, smoking parents, exposure to second-hand smoke, divorce or separation of parents, academic performance, and belief that smoking is harmful (79).
One of the findings of the present study was that being male is one of the risk factors for smoking in adolescents. In this regard, the meta-analyses by Haghdoost et al in 2013 (80) and Xi et al in 2016 (81) suggested that one possible explanation in this regard could be the difference in the lifestyle of boys and girls. Boys are more at risk and are more likely to smoke due to social conditions, curiosity, tendency to experience high-risk situations, peer pressure, and other health-related problems. In addition, the existence of social stigma regarding smoking in girls can be one of the reasons for a low tendency for smoking in girls. The present study revealed that smoking cigarettes among family members and peers as well as the consequent pressure were the most influential factors involved in adolescent smoking. For instance, Kumar et al maintained that family members, especially parents smoking cigarettes, affect adolescents. These adolescents probably accept smoking as a positive behavior. This would also help adolescents form positive subjective norms of smoking cigarettes (82). Moreover, research evidence showed that adolescents with more smoking friends exhibit more tendency to smoke cigarettes. Peers can influence adolescents in two ways: implicit effects such as adolescent imitation and explicit effects such as direct pressure to smoke cigarettes (83). Acceptance by friends during puberty is important; hence, adolescents seek to conform to their friends by ignoring their desires and gaining an identity (84).
Furthermore, the evidence from this study suggested that reducing cigarette smoking among adolescent male students should be addressed as soon as possible before entering high school. Implementing such plans should involve all beneficiaries, especially parents, peers, and school employees to be able to approach as an all-inclusive approach to achieve desired goals and reduce the rate of cigarette smoking among adolescents at school in the future. Prevention through health education should be a priority in all schools and society. Adolescents should be helped to learn how to control their behavior. Learning to say No to smoking offers and reject such offers are necessary. Further, adolescents' social norms, especially the values of cigarette advocates (e.g., adolescents who do not regard smoking as harmful) should change. Adults should stop smoking and set a good example for adolescents to help reduce this negative habit among this population.
Despite all effective factors identified in the present study, a number of factors were not taken into account due to the lack of available evidence. These factors include policy-making such as the price of cigarettes and legalization of cigarette smoking as well as genetic factors. Protective factors and their inherent nature are among the other factors that need to be considered. Are protective factors only the lack of certain risk factors or do they actually affect the relation? Some risk factors might directly (i.e., in the absence of protective factors) One limitation of the present study was that concluding and integrating all findings were difficult due to the different research methodologies, measurement instruments, and data analyses. Furthermore, this would make the comparison of studies difficult. In addition, the outcomes of these studies differ, and even when a certain outcome is labeled the same, different definitions may be involved. The majority of reviewed studies were cross-sectional in type which further limits the inference of a causal relationship between the factors and cigarette smoking behavior. Furthermore, the present study only employed Persian and English language academic papers excluding papers written in other languages. Moreover, the lack of access to all scientific databases was another limitation of the present study. Nevertheless, this study can provide a comprehensive insight into different effective factors in adolescent cigarette smoking.

Conclusion
The demographic features (e.g., older age, male gender, socio-economic status, receiving pocket money, level of education, and living in slums), family-related variables (e.g., less monitoring by parents, parents' level of education, warm and receptive environment for talks, satisfaction with the home environment, family conflicts, parents' divorce or death, mother's working outside the home, mother's anxiety, mother's smoking during pregnancy, adolescents' exposure to cigarette smokers in family and among friends, peers, teachers, and other social audiences) predicted cigarette smoking among adolescents. Moreover, psychological variables (e.g., stress and relieving stress, metacognitive beliefs such as negative beliefs in the uncontrollability and hazard of concerns, cognitive self-awareness, attachment styles, and depression (25)(26)(27)(28)(29), loneliness, low self-confidence, impulsivity, rebellious behavior, low behavioral control, the experience of self-damage, perceived susceptibility of health issues due to smoking cigarettes, and low perceived risk affected smoking cigarettes among adolescents (23)(24)(25)(26)(27). Other factors affecting adolescent smoking were the obsession with risky behaviors such as the previous experience of smoking cigarettes, consuming alcohol, tramadol, and marijuana, sexual behaviors and stimulating effects of cigarettes, emotional intelligence, inability to say No, gaining attraction and smoking cigarettes as a sign of maturity, psychological resistance, more curiosity, and failure at work (59)(60)(61)(62)(63). Sociocultural variables (e.g., family and peer pressure, mass media and commercial breaks in movies or on TV, cultural values of smoking, and religious beliefs), and educational and school-related variables (e.g., attitude toward and interest in school, wandering at school, academic performance, smoking cigarettes to help study better) were among the other factors influencing smoking in adolescents.
Among these, smoking by family and peers and their influence are the most prominent and common factors affecting smoking in adolescents. In addition, the evidence from this study suggests that to reduce smoking in adolescents, male students should be targeted as soon as possible before they enter high school. Similar to the present findings, it appears that cigarette smoking behavior is influenced by different factors such as personal, familial, social, and environmental factors. All these factors comprise part of the causal mechanism involved in cigarette smoking by adolescents. Considering the negative consequences of smoking, understanding the factors associated with smoking will help legislators and health professionals to reduce and prevent smoking among different classes, particularly among adolescents. However, future research should be developed to test this conceptual model. In fact, statistical testing of the model can evaluate the interaction of the factors and the effect size of each. Yet, this study can provide a comprehensive insight into different effective factors in adolescent cigarette smoking. This study is more comprehensive than studies that only looked into certain psychological or social factors. Given that several factors at different levels affect cigarette smoking in adolescents, differences in methods, tools, communities, and analyses in various studies prevent the aggregation and integration of results. Accordingly, designing and implementing programs that target different levels of influencing cigarette smoking in adolescents can be effective in preventing and reducing smoking among this age group.