The Study Impacts of population density on physical activity, BMI and Mental health of citizens in Mashhad

ABSTRACT
A healthy city is a city that continuously improves its physical, social, and cultural environments, develops its resources, and ensures public health. In recent years, the increasing trends of environmental pollution, unemployment, poverty, poor housing, and social and psychological harms as well as industrialization and the spread of epidemic diseases have decreased the quality of the urban living environment. Noorabad City, like many other cities, is facing many problems such as worn-out structures, inadequate housing, lack of social and health services, and noise pollution. These problems will cause serious damage to the health of the environment and citizens. The present study employs a descriptive-analytical method for final evaluation and data analysis. This study uses t-test and structural equation modeling to explain and model the effects. The results of the t-test of the sample showed that the status of healthy city indicators in the study area with an average of 2.51 is not in an acceptable situation and is estimated to be poor. Analysis of the findings of structural equation modeling indicates that the amount of factor load of the root mean square error (RMSE) is equal to 0.079, which indicates the desirability of the research model. Also, the analysis of the second-order factor model showed that the health dimension has the highest factor load with a weight of 0.94 and the lowest factor load belongs to the physical dimension with a factor weight of 0.64. In order to promote the indicators of a healthy city and balanced distribution of services and facilities, spatial policies and planning should be based on creating a platform for attracting more private sector investment and directing them to disadvantaged areas where the role of urban management and related organizations is very important.
Extended Abstract
Introduction
In the decades, attention to cities in the global sustainability agenda recognized by the official and unofficial sectors. This causes sustainability has become the priority in urban planning laws. Since cities have always been one of the key and powerful determinants in shaping people's health, with the introduction of the theory of sustainable urban development, health became one of the central issues in this theory. In recent years, the relationship between the characteristics of the built environment and public health has been the focus of many researchers. Because population density is one of the important dimensions of the urban built environment, the study of the effect of population density on people's health has also been studied in many studies, especially in developed countries. In these years, with the increasing criticism of urban sprawl in the framework of the theory of sustainable urban development, the policy of intensification of urban spaces based on the compact city theory has been proposed as a new approach to creating sustainable cities. In Iran, following the cutoff of government financial aid to municipalities since the early 1990s, and on the other hand, due to the Neglect of the government to create legal bases for obtaining sustainable incomes for municipalities after that, municipalities, especially in metropolises and large cities, were forced to Costs, try different methods. One of the most important and accessible, and efficient methods (Of course, only for municipalities) was to earn money through density sales, which has continued until today. With the generalization of the policy of density sales in Iranian cities and acceptance by municipalities, in recent decades, attention was directed to the negative consequences of density sales in various dimensions. Empirical literature review in Iran shows that despite examining the relationship between population density and urban issues in some research, there is no research regarding the study and analysis of the effect of population density on public health in Iran, while at the global level, especially in developed countries, since the late 1960s and early 1970s, over time, the study of the pathological effects of population density and crowding in urban environments has become one of the fields that have been the interest of various researchers.
This issue doubles the need to pay attention to the study of the effects of urban policies (specifically, the policy of density sales) on the public health of citizens. In particular, the densification of urban spaces in Iran has relied more on economic arguments to earn money for municipalities, and the various consequences of this policy on the quality of life of citizens, especially their health, have not been paid attention to at all. In line with this goal, which is to analyze the effects of population density in the urban environment on the health of citizens, Mashhad city was selected as the second largest city in the country for investigation and analysis.
Since the field of health is very broad and includes various physical, social, and psychological dimensions, in this research, the two fields of mental health and physical activity and mobility (as one of the sub-sections of physical health and also a very important factor affecting mental, social and physical health) were selected for investigation and study.
According to the purpose of the research, the main questions of this research are: 1- Has population density increased the level of physical activity and walking of people? 2- Has the increase in population density in urban areas improved people’s mental health? And 3- Has the increasing population density in urban areas reduced people’s body mass index?
 
Methodology
This research is classified as descriptive, case-study, survey, and cross-sectional. Collecting data for different parts of the research has been done with the help of documentary and survey methods. For data on the independent variable (population density), use the information from Mashhad municipality. Among the 140 neighborhoods of Mashhad, 13 were selected, of which 4 had low population density, 6 had medium population density, and 3 had high population density. The statistical society is the citizens of Mashhad 25 years old and above, and the sample size is equal to 950 people. Using the cluster sampling method to select the target neighborhood from among the 140 neighbors of Mashhad city (according to population density and geographical location) and at the local level also using the simple random sampling method to select Citizens and individuals was used for questioning. The measurement method of mental health was the mental and oral health measurement. General Health Questionnaire-28 is used to measure people's mental health. Cronbach's alpha coefficient was used to check the reliability of the research tool. Cronbach's alpha coefficient was equal to 0.883 for all items, 0.820 for Sharkey's physical activity intensity index, and 0.908 for Goldberg's standard mental health test. The coefficients related to the five sub-sectors of mental health also varied between 0.735 and 0.903. These coefficients indicate the very appropriate reliability of the research tool. The Sharky index and people's daily walking uses to measure physical activity. Since that studies have shown a direct relationship between the amount of walking and the level of physical fitness, we can use the amount of people's daily walking to predict the level of physical fitness. In addition, Body Mass Index is used to measure people's health-oriented physical fitness.
 
Results and discussion
The results show no significant difference between the study areas in terms of physical activity (Sharkey index) and body mass index. But in terms of people's daily walking and mental health, significant differences between different neighbors were observed. The analysis of data related to population density (gross density and net residential density) with physical activity showed that in the studied areas, population density had negative effects on people walking. The data shows that the dose of people walking in low and medium densities is more than in high-density areas. While in low-density spaces, 12% of people walked more than 120 minutes a day, In high-densities, this reaches 3.8%. The analysis of correlation coefficients also showed that either gross residential density or net residential density has a significant but inverse relationship with the daily walking rate of people.
Also, the analysis of the physical activity intensity data (Sharki index) with the population density showed that there is no significant relationship between the population density (gross and net residential) and the physical activity intensity of the people. However, the data indicates that residents of medium-density neighborhoods participated in physical activities more than residents of low-density and high-density neighborhoods. Based on data of research, the residents of high-population density neighborhoods have less desire to exercise, and regular physical activity than the residents of low and medium-density. For example, while only 11.3% of the residents of the neighborhoods With high density have participated in different types of physical and sports activities on average three times or more during the week, this ratio is equal to 18.6 percent for medium-density areas and 16.3 percent for low-density areas. This finding indicates that localities with an average density between 100 and 150 people per hectare have more potential to encourage people to participate in all kinds of physical and sports activities.
The analysis of data related to body mass index and their relationship with population density showed that no significant relationship between gross residential density (r = 0.014; Sig., = 0.665, n=941) and net residential density (r = 0.050; P = 0.122, n=941) was not observed with body mass index.
More findings indicate that in the studied areas, 22.2% of respondents were healthy, 55.7% had mild, 21.4% had moderate, and 0.7% had severe disorders. Correlation analysis uses to investigate the relationship between population density (gross and net residential density) and mental health. The results show no statistically significant relationship between net residential density and mental health (either overall mental health or its components). Based on the findings, a significant relationship can be seen between gross residential density, mental health (total), and two of five constituent components, including physical symptoms and anxiety. The correlation coefficient related to overall mental health and physical symptoms are equal to 0.079 and 0.102 at a 95% confidence level, and the anxiety correlation coefficient is 0.115 at a 99% confidence level. According to the coding type of the questionnaire, a positive correlation means that an increase in population density will be accompanied by a rise in mental health scores. Considering that a higher score means less mental health, we can conclude that the results of the inferential analysis also indicate the negative impact of population density on people's mental health. Of course, since the correlation coefficient between 0 and 0.29 implies a weak correlation between two variables, it can be concluded that the relationship between population density and these two variables is also very weak.
 
Conclusion
The literature review of research in Iran determined that despite examining the relationship between population density with urban issues in some research, no research has been done regarding the study and analysis of the effect of population density on public health and its dimensions. Based on this, the most important innovative aspect of the research can be seen in the newness of the subject in Iran, so perhaps this research is the first research that has examined the relationship between population density and mental health and physical activity and obesity of citizens.
Due to the lack of similar studies in Iran, comparing the results is impossible. However, a review of some related research shows that population density has negative effects on the quality of life of citizens. Our research indicated the need to conduct much more experimental research regarding the pathological investigation of urban density in various dimensions of citizens' lives. Pay attention to the observed correlation between population density and mental health and physical activity is very weak; however, the results of this research are somewhat in line with the results of Haidarzadeh and Behzadfar (2018), Madani et al. (2016) and Jumapour et al. (2011) regarding the harmful effects of population density on the quality of life of citizens.
 
Funding
There is no funding support.
 
Authors’ Contribution
All of the authors approved the content of the manuscript and agreed on all aspects of the work.
 
Conflict of Interest
Authors declared no conflict of interest.
 
Acknowledgments
We are grateful to all the scientific.