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Smoking among High School Students in Iran: A Meta-Analysis Study

Objective: Cigarette smoking is an important and preventable risk factor, especially for adolescents and high school students. This issue has become one of the challenges for health system. Thus, the present study aimed to investigate the prevalence of smoking among Iranian high school students. Method : This systematic review and meta-analysis study was done by searching PubMed, Scopus, Web Science (WOS), Science Direct, SID, and Google Scholar using the following keywords: “student” and “smoking” from 2000 to March 2018. After initial and critical appraisal, data were entered into a checklist and analyzed by a comprehensive meta-analysis software. Results: The prevalence of smoking was 7.9% by combining the results of 49 articles. Males and females had 10.6% and 4.5% smoking prevalence, respectively. The overall prevalence of smoking was higher in northern areas in Iran (22.4%). Males in the northern (22.4%) and females in western regions (5.3%) were more smokers. There was a significant relationship between the prevalence of smoking with the year of publication, sample size, and age (P < 0.001). Conclusion: In this study, Students' tendency to smoke was different in various regions of Iran, and had a high rate (7.9%). This figure indicates the necessity for planning some coherent educational programs for the public.

Smoking, one of the most important health threats, kills millions of people annually. As reported in 2016, there were more than 7 000 000 victims of tobaccorelated illnesses (1). It is estimated about 80% of deaths will be related to smoking and tobacco in 2030, and the current trend of death is continuing (2,3). Worldwide, 1852 billion dollars are the annual cost for smoking (4), and more than 150 billion dollars are spent for healthrelated problems due to smoking (5). In Iran, approximately 1740 million dollars is spent on smoking each year (6), and 5.220 billion dollars is dedicated to cure tobacco side effects in the health system (6). The prevalence of smoking among adolescents is increasing (7). The negative effects of smoking on health have fully been documented, however, adolescents and young adults perform other high-risk behaviors that accompany smoking, causing excessive risks (8,9).
Smoking is coupled with bowel disorder, chronic obstructive pulmonary disease, cardiovascular malfunction, cancer risk, and increasing in severity of respiratory illnesses (10)(11)(12)(13)(14). It accounts for 71%, 42%, and 10% of lung cancer, chronic respiratory diseases, and cardiovascular disease, respectively (15). Students constitute a crucial part of the population (16), thus, smoking among this group has attracted more attention from the World Health Organization (WHO) (17). Adult smokers commonly start smoking when younger than 18 years, a critical period for preventing smoking (18). There are various findings on the prevalence and factors of smoking among Iranian students. Roohafza et al (2018) in Isfahan, Iran, showed that the prevalence of smoking was 17.5% and the common factors were depression, attitude toward smoking acceptance, and risky behaviors (19). In another study by Karimi et al (2018) in Tabriz, Iran, the prevalence of smoking among boys and girls was 22.6% and 17.2%, respectively, and age, living with parents, smoking friends and family members, risk-taking behaviors, self-harm, attitudes, and positive thinking about smoking were significant factors correlated with smoking (20). In another study by Nosrat Abadi et al (2017), the prevalence of smoking among students was 33.4%, and an inverse correlation between smoking and emotional appraisal and mindfulness was found (21). The age of smoking is considered as one of the most important determinants of dependence on tobacco and the possibility of not-quitting smoking, which maintains the risk of unintended health outcomes. Those who start smoking during adolescence are among more heavy smokers during adulthood, thus, they have the highest mortality rate due to smoking. Therefore, the best time to take the necessary measures and implement preventive strategies for smoking is in adolescence period and even before that. With regard to increasing the prevalence of cigarette smoking among high school students (19-21), as the significant portion of the population, it is suggested that the rate of cigarette smoking be taken into account. Because of the diversity of the studies in Iran, this study was conducted to determine the prevalence of smoking among Iranian high school students.

Materials and Methods
In this systematic review and meta-analysis, the prevalence of smoking in high school students of Iran was investigated. The research question was designed based on the PEO, which is as follows: What is the prevalence of smoking among Iranian students?

Search Strategy
In this study, the articles published from 1998 to March 2018 were investigated. Two researchers (M.N, Ar.A independently searched PubMed, Scopus, Web of Science (WOS), Science Direct, SID, and Google Scholar using the keywords of "cigarette", "tobacco", "students" and "Iran" (both in English and Persian

Results
In this study, 548 articles were identified. After excluding the duplicates, 240 articles underwent initial evaluation. Of them, 69 were critically appraised, and eventually 49 papers were eligible for data extraction and analysis (Figure 1). A total of 19 studies whose fulltext were not available, or whose full text did not mention smoking were excluded. The results of the Eager test showed that publication bias of the studies was significant (P = 0.002; Z = 2.825). This value is also visible in the funnel plot ( Figure 2). Most studies were of medium to high quality. According to the STROBE checklist, 38 of these studies were desirable and 11 were undesirable. The quality of the selected articles is presented in Table  The highest and lowest overall smoking prevalence was related to Gilan (28.2%) and Zahedan (1.6%). These rates belonged to males were taken in Yazd (35.2%) and south Khorasan (3.9%), and smoking in females were respectively more prominen in Karaj and Sistan and Baluchestan provinces ( Figure 4). The results of the meta-regression test indicated with increasing mean age (Q = 9364.58; P < 0.001), and year of study (Q = 10270.84; P < 0.001), the prevalence of cigarette smoking was increased, however, this rate reduced with increasing the sample size (Q = 10270.84; P < 0.001).

Discussion
This study is the third meta-analysis and systematic review of the prevalence of cigarette smoking on Iranian students after Rahimi Moaghar et al (2012)  showed that the prevalence of lifelong smoking among students was between 50% and 80% (29). Other studies in Cyprus and China reported the prevalence of smoking was 48% and 38% to 58% (30)(31). Also, the results of this study showed that students aged 16 to18 years old had the highest rate (10.6%) of smoking. In other countries, the rate in this age range was 16.1% to 18.9% (32)(33)(34). In comparison with other studies (29-34), our results demonstrate a lower prevalence of smoking. It seems that with regard to the reducing of the population rate in Iran during recent years by decreasing birth rates, family supervision has improved on children. This would accompany with less smoking and other risky behaviors among high school students, which demanded more studies . The prevalence of smoking among males was 10.6%. This rate was 30.9% in another study in Iran (27). However, Mehrabi et al (2004) showed that the prevalence of cigarette smoking was 7.1% in men aged 15 to 24 years in Iran (35). Other studies in different nations reported this rate as 2.1% to 31.4% (36)(37)(38)(39). The smoking has raised to the maximum level in developed and developing countries, however, it is declining slowly overtime (40). Our study also showed that the incidence of smoking among students has reduced during the 2 recent decades, which could be associated with Iran's Health Ministry planning according to the warnings and concerns of the WHO regarding global increase of smoking (3). In this respect, families as the main pillar of the society could enhance their intimate relationship with children, change their attitudes towards smoking, and use effective management means to reduce adolescent smoking (41). Furthermore, it is most important for schools and the community to have a comprehensive preventive program for smoking among students (42).
Our results represented that the prevalence of cigarette smoking was 4.5% in female students. Mehrabi et al (2005) showed the prevalence of smoking in females aged 15 to 64 and 15 to 24 years was 0.9% and 0.3%, respectively (35), which is lower than our study. Studies in other countries show that female students in Malaysia, Norway, Poland, and Enggland had the prevalence of 2.4%, 0.6%, 9.6% and 7%, respectively (36)(37)(38), indicating almost higher prevalence of smoking among Iranian female students compared to their peers. In developed countries, the prevalence of smoking among women is decreasing, and the trend is steadily increasing in developing nations (40). Because of the cultural and social reasons and constrains, it seems that the actual prevalence of cigarette smoking among Iranian female students is higher than the results of the present study. It is believed that the prevalence of smoking in Iranian female students in the last 2 decades has had a declining trend, which shows the correct and coherent planning in this area (3). However, despite the WHO recommendations, smoking rates among Iranian female students are high, but industrialized nations have done a great deal to reduce and prevent cigarette smoking and have successfully implemented programs aimed at improving students' awareness and changing their attitudes and behaviors regarding smoking (43). Given the high prevalence of cigarette smoking by Iranian students, it is needed to implement policies by the government to reduce tobacco use, adopt appropriate and applicable strategies such as advertising, warning videos, enhance cognitive skills, and improve lifestyle (42).

Limitation
Due to the different variations in the prevalence of nicotine use at different times and places, one of the limitations of this study was to present the prevalence of smoking as mean/median. Another limitation of this study was the limitation of Iranian databases that could not combine different keywords. Another limitation of our study is that we specifically looked at the prevalence of smoking, not other tobacco products.

Conclusion
In this study, the prevalence of cigarette smoking was different in various regions of Iran and the overall prevalence was 7.9%, and the prevalence was higher among male students. Given the importance of smoking prevalence among students and the lack of attention to this issue in most Iranian schools, planning for strict preventive measures is highly recommended.