Introduction

A school is an ideal place for health promotion, and it can provide an appropriate environment for education and practice of positive health behaviors (1). Children spend a significant part of their time at school. So, schools are considered as a potential environment influencing the children's health (2). Schools can play a major role in improving health in children to become healthy adults. In general, children and adolescents attend school five days a week; so, they spend much of their time at school. In addition to acquiring academic skills, students can also learn cultural and social skills that strongly affect health behaviors (3).
Health education is an inseparable part of the education curriculum for all students. Health education curriculums should represent the essential knowledge, attitudes, and skills. Health education programs are designed to promote a healthy life and eliminate high-risk health behaviors among students (4) and make them feel more responsible for their health. Health education is the basis of health promotion, including school health promotion and other important components (5). Regarding the Ottawa Charter emphasizing education as a health requisite, WHO has introduced schools as promoters of health. Comprehensive health education programs in schools and parents and societies' participation in health promotion programs have been emphasized as major health promotion components (6, 7).
According to the above statements, health is considered as one of the essential human needs. This concept is considered as physical, mental, and social welfare by WHO, and policymakers have always paid it attention. Fortunately, policymakers of the education system have also paid attention to the importance of health issues. They believe achieving its ultimate goal is to realize healthy life; the education system should not ignore the health dimension. One of the fundamental aspects of education is considered biological and physical aspects that directly focus on health promotion (8).
  ● In 2002, UNESCO developed a program titled "Teaching and learning for a sustainable future" for students; one of the four themes of this program curriculum was health education (9).
● Also, principle 29 of constitutional Law has introduced health as a public right. As teachers are responsible for educating the future generation, they and their students should be provided with curriculums, including health promotion considerations (5).
WHO studies on health behaviors in 35 countries (2015) suggest that about 60% of people's health and quality of life depend on their lifestyle and personal behaviors. Borhani (2014) found that the adolescents' health promoting behaviors is not at the same level, and it can be due to their personal characteristics (10). Also, Sahi, Ebrahimi, and Mohammadi reported that 70.9% of students are at a medium level of health-promoting behaviors, and their lowest scores have been obtained in stress management, physical activity, and nutrition components (11). In the current conditions in Iran, we need to promote health components in different groups of the society, including teachers, to have a more healthy society.
A national study performed in 5 provinces to investigate people above 18 years old suggested that health literacy is at a low level in Iran. Moreover, a study performed in 2012 showed a low level of health literacy in Kerman province (7).
So, despite the importance of health education, studies suggest that this issue has not been paid enough attention in Iran; different classes, especially teachers and students, are not provided with health-promoting programs. Although no study has yet investigated health literacy among teachers and teacher training students, some of the findings of health-related studies can be useful in this area. Imani, Rakhshani, and Tabatabaei (2004) found that only one percent of elementary school teachers have adequate information about environmental health and the students' physical and mental health needs.
The findings mentioned above can be considered as a threat to the quality of education of future teachers and students; because the time students spent at school is more than the time they spent with their parents. According to Eisner (1992), a school is an ideal place for health promotion (12). So, increasing the teachers' health literacy provides a condition in which they will try to promote their own and their students' health. Besides, the health-promoting school program has been applied in Iran since 2010. The successful operation of health-promoting school programs will not be realized without defining health promotion for teachers. Furthermore, a comparative investigation of Iranian students and students from the four countries of Japan, Australia, France, and Turkey showed that obesity, malnutrition, smoking, oral and dental health problems, venereal diseases, and high-risk behaviors are increasing in Iran.
Nekouei Moghadam et al. (2010) reported that the content of health education textbooks had no effect on students' ability and attitudes and had not acquired enough skills (13).
To make change, prevent diseases, and promote human force health that are considered the goals of health system transformation plan, health education should be focused in different classes of society, especially students at younger ages. Since the school system directly affects children and adolescents and an indirect effect on adults, it seems that optimal health education in elementary programs is one of the simple ways to provide health education for the general public. According to the investigation of health education status in elementary school textbooks and content analysis of health information components in middle school textbooks, there should be more attention to different health education dimensions in these books. Moreover, some of the health information components have not been paid enough attention in textbooks (14-15). Therefore, health education and promotion can provide students and teachers with the opportunity of acquiring knowledge, information, and skills that will lead them towards appropriate health behaviors and habits. So, designing patterns and planning for education, improving negative health behaviors, and creating health-promoting behaviors in elementary school students is unavoidable (16). Hence, this research aimed to investigate the content of fourth-grade elementary school textbooks in terms of the health system's assumptions and check the extent to which these assumptions are observed in educational materials.
Methods
This qualitative  study  was performed via content analysis using Shannon Entropy Technique. The unit of analysis is the page (texts, questions, drills, and pictures). Content analysis is done in different stages. Three major stages include the following:

1. Pre-analysis (preparation and organization)
2. Review of the materials (message)
3. Processing of the results (17)

This research is mainly focused on the third stage of content analysis that is processing the collected data of the message. After coding and categorizing the message, the obtained data were analyzed. Nowadays, various techniques have been proposed in this area based on getting the percentage of the categories frequency. These techniques have special mathematical problems that decrease the reliability of their results. This research tried to process the results by a new method that is based on the systems theory. The used method is Shannon's entropy which proposes a new qualitative and quantitative approach to content analysis. This method is a very strong and reliable way of content analysis. In information theory, entropy is an indicator for evaluating uncertainty expressed by a probability distribution (18). Based on this method that is referred to as the compensatory method, the respondents' viewpoints about the content (fourth-grade elementary school textbooks) and 12 major components and 8 minor components of health education and promotion were investigated. The validity of health education and promotion was evaluated based on health experts' viewpoints and the curriculum. To ensure accuracy of the analysis results, the upstream documents were analyzed by the researchers and six health education experts. For the same perception of the content analysis form, the researchers' viewpoints about health education, its components, and units of analysis became coordinated.
Step 1: Frequency matrices of the frequency table should become normalized by the following relation:
 (1)- 
F=frequency of the component                              
P=normalized frequency matrix
Step 2: Information load of every category is calculated and included in the related column. It is done by the following relation:

Step 3: Coefficient of importance is calculated by the information load of indicators. The indicator with a higher information load will have a higher degree of importance (W_j).

 Due to the occurrence of error and infinite answers in mathematical calculations, to calculate JE, JiP values equal to zero have been replaced by a little number, i.e., 0.00001. JW is an indicator specifying the importance coefficient of each category of a message regarding the respondents. On the other hand, the message categories have also been ranked based on the W vector (19).
This research tries to investigate health education and promotion components in fourth-grade elementary school textbooks. According to Hiroshi (2012), health-related habits should be acquired in the early stages of life to prevent adulthood's physical and mental diseases. For this purpose, related rules should be developed, and necessary educations should be provided for people. In this research, we have investigated 12 components of health education and promotion. According to previous studies, each of these components includes several subcomponents presented in the following table. The components and indicators studied in this research have been extracted from studies performed by Helm Seresht and Delpisheh (2009), Shah Hosseini (2016), Shadarzi (2015), Eskandari (2015), Jamison (2001), Ackerman (2004), Lason (2003)(20). However, no study has independently investigated health education and promotion in fourth-grade elementary textbooks yet. The research components and indicators were derived from previous relevant studies, doctors' and health experts' viewpoints, and books. After determining the evaluation indicators, health education, and promotion components, the data were collected and analyzed by Shannon's entropy. In this way, fourth-grade textbooks have been investigated to the extent that health education and promotion components have been addressed.
Results
The findings include qualitative and quantitative analysis of the components found in all the fourth-grade elementary textbooks based on the health system components. First, the frequencies were obtained for each component, and they were converted to normalized data according to the first step of Shannon's entropy method. Then, according to Shannon's entropy's second step, uncertainties of the data are included in the tables. After that, according to Shannon's entropy's fourth step, coefficients of importance are determined for the data. In this way, the component with the highest importance is specified.

According to Table 1, among the components studied in 6 fourth-grade elementary school textbooks, the highest frequency (277) has been reported for mental health, and the lowest frequency (12) has been reported for disability. Among
the 1157 health components in fourth-grade elementary textbooks, there are 81 physical health components, 263 nutritional health components,
57 environmental health components, 33 natural environment health components, 227 family health components, 19 safety incident components, 73 physical activity components, 277 mental health components, 25 component of prevention of high-risk behaviors, 14 components of disease control and prevention, 12 disability components, and 58 components of public health and school health.