The study found across three GSHS in 2005, 2011 and 2017 in Lebanon significant decreases among both boys and girls in interpersonal violence (bulling victimization, being physically attack and involvement in physical fighting), inadequate hand hygiene (after toilet use), and suicide plan, and among girls only suicidal ideation, loneliness and worry-induced sleep disturbance. Significant increases were found among both boys and girls in the prevalence of inadequate fruit consumption, and among boys only unintentional injury and inadequate hand hygiene (before eating). In a “prospective observational study involving 50 schools from different areas of Lebanon, around 70% of the involved schools offered health-related courses in their curricula” . “Dental health (74%), smoking cessation (72%) and physical activity (68%) were among other most addressed topics, while mental health was the least discussed (20%).”  “The study findings suggest that despite weaknesses, the majority of the sampled schools had either implemented or were in the process of implementing a health promoting school programme to improve health education and students’ well-being.” Following implementation of a network of health promoting schools (HPS) in Lebanon in 2010, a cross-sectional evaluation comparing HPS with non-HPS was conducted in 2011-2012, which found no significant differences between HPS and non-HPS in the assessed risk behaviours (drug use, smoking and alcohol use) .
Violence-related behaviour (being bullied, physically attacked and participation in a physical fight) decreased in this study, which concurs with four other studies [14,24-26], while a few studies found an increase in one or more types of interpersonal violence, e.g., in Oman , the Philippines  and Venezuela . In several older studies among adolescents in Lebanon, high rates of interpersonal violence have been reported [5-7], which compares with our high rates of interpersonal violence in the 2005 GSHS. It is possible that the high rates of interpersonal violence in 2005 were still related to the post-conflict situation in Lebanon, which subsequently subsided so that interpersonal violence decreased from 2005 to 2017. On the other hand, injury prevalence increased in this study among boys, while in the trend study in the Philippines a similar increased was observed , in Oman, no significant trend differences were found  and in Morocco a decline in the prevalence of injury among adolescents was found . Considering the high proportion and significant increase in annual injury prevalence in this study intensified safety promotion and injury prevention programming is indicated in Lebanon.
The prevalence of inadequate fruit and vegetable intake was high in the 2005 GSHS and increased for fruit intake over the study period, which was also shown in a trend study in Oman  and other countries in the Arab region . The experience of hunger (or food insecurity) was low and did not significantly differ among boys and girls over time. In a national survey among adolescents conducted in 2015 in Lebanon, a high prevalence of household food insecurity (55.2%) was observed , which may explain the high prevalence of food insecurity in our 2011 survey.
The prevalence of sub-optimal oral hygiene (tooth brushing <twice/day) was high across the three school surveys (almost 40%), much higher than in a study among school adolescents in four Southeast Asian countries (22.4%) . In a survey among adolescent students in Beirut, also a high prevalence of sub-optimal tooth brushing was found , calling for oral hygiene health promotion programmes targeting schoolchildren and their parents . Although poor hand washing after toilet use decreased between both sexes, poor hand washing before eating increased among boys in this study. In the Oman trend study sub-optimal hand hygiene pattern increased , while it decreased in the Philippines . It is possible that poor hand washing after toilet use decreased among adolescents in Lebanon from 2011, after the “Call to Action for WASH in Schools campaign was formally launched in 2010” in Lebanon .
Regarding mental health indicators (having no close friends, loneliness, worry-induced sleep disturbance, suicidal ideation and suicide plan), suicide plan decreased among both boys and girls, while loneliness, suicidal ideation and worry-induced sleep disturbance decreased among girls only. In comparison, in the Philippines trend study, the prevalence of suicidal ideation and suicide plan decreased among boys and suicidal ideation increased among girls over time . As found in previous investigations [9-11], poor mental health, such as suicidal behaviour and anxiety-related disturbances, has been identified as a significant problem among adolescents in Lebanon.
In terms of protective factors, school attendance, peer support and the three parental support indicators (supervision, connectedness and bonding) did not change over time among both boys and girls. In the Philippines trend study protective factors did not change over time , in the Oman trend study only one of the protective factors (peer support) improved over time , while in New Zealand trend study positive family and school connections improved over time .
The current study results may inform public health intervention programmes targeting specific health risk behaviours among adolescents in Lebanon. For example, specific school food environment policies, such as direct provision of healthful foods/beverages, can improve targeted dietary behaviours, such as fruit and vegetable intake . Universal school-based interventions that target multiple-risk behaviours, may be effective in preventing engagement in substance use, including alcohol use, among young people . There is “good evidence that various whole-school health interventions are effective in preventing bullying.”  School dental health education can improve oral hygiene practice behaviours, such as frequency and duration of brushing, of school children
[35,36]. Increased implementation of multi-level (training, funding and policy) “hand-washing interventions can reduce the incidence of diarrhoea, respiratory infections, and school absenteeism.” Universal resilience-focused interventions (particularly cognitive-behavioural therapy-based approaches) may be used for reductions in poor mental health (depressive and anxiety symptoms) for children and adolescents .
Limitations of the study
“Secondary education enrolment ratio” was 80% in Lebanon in 2005, 76% in 2011 and 63% in 2017 , yet this school survey did not represent all adolescents in Lebanon. Some study variables (such as sedentary behaviour, tobacco use, sexual behaviour and physical activity) were not included in this analysis, since they had not been assessed in all the three Lebanon GSHS. Although self-reported weight and height was collected, the missing values were in the wave one survey more than 30%, and therefore body mass index was not included in this report. Further, the study is limited because of its cross-sectional design and self-reported data collection.