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Prevalence of stunting in Iranian children under five years of age: Systematic review and meta-analysis

Background: Children in all countries, especially in developing countries, constitute a vulnerable group. Therefore, attention to their health issues is very important. The aim of this study was to determine the prevalence of stunting in Iranian children under-five years. Methods: All original studies were searched by complex search syntax from international databases including Medline (PubMed), Web of sciences, Google scholar, Scopus, CINHAL and the Iranian databases consist of SID (Scientific Information Database, www.sid.ir), Irandoc (Iranian Research Institute for Information Science and Technology, Irandoc.ac.ir), Iranmedex (www.iranmedex.com), and Magiran (www.magiran.com) from January 1989 to August 2017. Two independent reviewers identified relevant studies in several steps. We employed a random effect model to generate a pooled prevalence. The reported prevalence is presented as percent and 95% confidence interval (CI). Sources of heterogeneity among the studies were determined using subgroup analysis and meta-regression. Results: Finally, 16 studies from different settings remained for meta-analysis in order to have a pooled prevalence estimate, which prevalence of total stunting was 12% (95%CI: 10–14). Subgroup analysis for gender showed that the prevalence of stunting in both boys and girls children were equal to 10% (95%CI: 8–11) and 9% (CI 95% 8–10), respectively. Also pooled prevalence of stunting in southern provinces are higher than other provinces. Conclusion: The prevalence of stunting in some regions of Iran is higher than others. Although, in recent years much effort has been made to address deprivation such as economical, nutritional and social supporting, improvement of the quality of life, there are still nutritional problems in these areas of Iran.


Introduction
Children in all countries, especially in developing countries, constitute a vulnerable group. Therefore, attention to their health issues is very important. Protein Energy Malnutrition (PEM) is a common nutritional problem in children under the age of 5 years (1,2). The PEM in the first years of life leads to growth retardation, 2 stunting, and reduction of the mental development of children with repeated infections, resistance to treatment and reduced physical activity (3,4). The malnutrition is a major cause of reduction of lifetime and pathogens in children, and malnourished children are at higher risk of illness and death than healthy children (5)(6)(7). Generally, about 60% of more than 7 million deaths in under-five children are attributed to malnutrition (8). The malnutrition can have irreversible consequences in the first years of life.
In the world, about 25% of children under the age of 5 suffer from stunting, and it is estimated that 80% of these children live in developing countries. This is a tragedy for 165 million children under the age of 5 who are suffering from stunting (8). Of every 5 children in developing countries, a child has malnutrition and malnutrition is associated with half of all deaths of children in the world (5,9).
The global estimates of malnutrition indicate that 35.8% of pre-school children are underweight, 42.7% of them are stunting, and also 9.2 % are wasting in the developing countries (10). Usually, the WHO standards and NCHS (National Center for Health Statistics) are used to assess child growth and also malnutrition. Initially, WHO (World Health Organization) standards based on Multicenter studies were collected and designed in Brazil, Canada, India, Norway, Oman and America between 1997 and 2003, and in 2006, WHO provided new standards for assessment of child development. The WHO standard includes weight for age, height for age and weight for height and BMI for age for girls and boys 0 to 60 months old (11).
The studies have shown that the prevalence of stunting in children under-five is 26% in the world, but this figure was 26.8% in Asia (12). The different studies have been conducted on the prevalence of malnutrition in Iran, but most of these studies are at the provincial level, and studies at the national level are limited. However, the estimated prevalence of these studies are different. For example, the study by Houshiar Rad et al. showed that the prevalence of stunting, underweight and wasting in Iranian children under-five years are 13.1, 7.6, and 4.5%, respectively (13). Another study in Fars Province (Iran) showed that the rates of stunting, underweight, and wasting are 9.53%, 9.66%, and 8.19%, respectively (14). Study of Esfarjani F et al. showed that the prevalence of stunting is 3.7% among children in Tehran (15). Therefore, given that the different prevalence estimated at the provincial and national studies and also the importance of the nutritional status of children under 5 years old as an important health indicator, the aim of this study was to determine the prevalence of stunting in Iranian children under-five years.

Inclusion/Exclusion Criteria
We reviewed the search results, and then excluded some studies after reviewing the titles. The evaluation of searched studies was done based on inclusion and exclusion criteria by two reviewers individually (MY, MK). The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement was used as a guide to enhance the quality of reporting in this review. In this study, inclusion criteria were 1) cross-sectional design of the study, 2) report of estimated prevalence of Stunting, Growth Disorder, Stunted Growth, Stunting's and PEM in the paper, 3) study on populations younger than 5 years; exclusion criteria were 1) interventional studies and other types of studies except for cross-sectional, 2) animal studies, 3) studies on populations older than 5 years.

Data extraction and Quality assessment
The qualities of all studies were assessed by Modified Newcastle-Ottawa Scale for cross-sectional studies (16,17) and PRISMA checklist (7, 18-21) by two reviewer independently(MY, MH). Under supervision by the reviewing team, checklist including the following factors were filled :1) name of first author, 2) date of publication, 3) date of study, 4) total sample size, 5) sampling method, 6) study design, 7) number of female and male cases, 8) type of questionnaire, 9) score of appraisal tool, 10) main variable, 11) prevalence of malnutrition, stunting, growth disorder, stunted growth, stunting and PEM based on their questionnaire, 12) inclusion criteria. Additional information on study results was extracted with respect to the type of instruments.

Statistical Analysis
We employed random effect model to generate a pooled prevalence. The reported prevalence is presented as percent and 95% confidence interval (CI). The heterogeneity between the included studies will be assessed using the I2 heterogeneity statistic, reported as percentage (%), to determine the extent of variation between the studies. Forest plot also was used to present result of meta-analysis schematically. Subgroup analysis was conducted on the gender, and geographical region, and meta-regression was performed to examine the impact of year of publication on prevalence.

Results
Our primary search yielded 242 papers. After reviewing the titles, 132 papers excluded due to duplicating or unrelated papers. From the remained 32 papers, based on the developed checklist articles were excluded (Fig. 1, Table 1). The included papers were categorized in two groups according to their study design (descriptive or analytical cross-sectional studies).

Assessment of Pooled Prevalence
Finally, 16 studies from different settings remained for meta-analysis. Prevalence of total stunting was 12% (95%

Discussion
The present study was a meta-analysis study which was designed and implemented to determine the prevalence of stunting in Iranian children under-five years. The results of this study showed that the pooled prevalence of stunting in Iranian children under-five years is 12% (95% CI: 10%-14%), regardless of gender. While the subgroup analysis for gender showed that the prevalence of stunting in boys and girls are similar and equal to 12% (95%CI: [10][11][12][13][14]. Also, the estimate of pooled prevalence of stunting based on the subgroup analysis for different regions of Iran showed that the prevalence of stunting in western, eastern, southern and central regions are 9% (95%CI: 8%-10%), 8% (95%CI; 7%-8%), 17% (95%CI: 1%-34%) and 15% (95%CI: 10%-21%), respectively.
The results of this study showed that the pooled   (2000-2002), a number of 7158 households were selected using systematic sampling from 28 provinces of Iran and, generally, 2562 children were examined. Their results showed that the prevalence of stunting for children under 5 years was 13.1% (95%CI: 11.8%-14.4%) (13). As it is seen, the results of this study are not consistent with our study, and the prevalence in our study is almost two times lower; but other studies are more consistent with the results of this study. For example, the data extracted from "Iranian National Study of Malnutrition Prevalence" has showed that prevalence of stunting is 4.7% in Iranian children in 2008 (22). In another study conducted to investigate the determinants of stunting in first grade primary school children of Tehran, the results showed that the prevalence of stunting is 3.7% in the study population in 2013 (23). In fact, it can be said that, we are seeing a decrease in the prevalence of stunting in Iran, of course, the decreasing trend of stunting has been reported in South East Asia and world (24,25). This can be explained by improved primary health care during pregnancy and early childhood, breastfeeding and growth monitoring. In our study, the subgroup analysis for gender showed that the prevalence of stunting in boys and girls are similar and equal to 10% (95%CI: 8-11) and 9% (95%CI: 8-10), respectively. The national study by Houshiar Rad et al. to determine the prevalence of stunting, underweight, wasting and overweight among children under five years (2000)(2001)(2002), showed that the prevalence of stunting in boys and girls were 14.2% (95%CI: 12.2%-16.1%) and 11.8% (95%CI: 10.1%-13.6%), respectively (13). The report of the children's nutritional statusin the provinces of Iran showed that the prevalence of stunting in boys and girls were 16.8% and 13.9%, respectively (26). A study by Esfarjani et al. showed that the prevalence of stunting in boys and girls are 2.8 % and 4.4%, respectively (23). Most of the studies carried out in this field show that the prevalence of stunting in girls is higher than boys (27)(28)(29). This difference may be due to more attention and care of the families to the boys, which is related to the false beliefs and cultural problems of that society (30). Some studies have also shown no significant difference between the two sexes. The study of Nouri Saeidlou showed that stunting rates in girls higher than boys but differences were not significant (8). A study by Davoodi and colleagues showed that there is no significant statistical difference between boys and girls in Hamadan (31).
In the present study, the estimate of pooled prevalence of stunting based on subgroup analysis for different regions of Iran showed that the prevalence of stunting in the western, eastern, southern and central regions are 9% (95%CI: 8%-10%), 8%(95%CI: 7%-8%), 17%(95%CI: 1%-34%) and 15% (95%CI: 10%-21%); respectively. The study by Karajibani et al. in children under six years in Sistan-and-Baluchestan province which is located in south-east of Iran showed that the prevalence of stunting is 32.1% (32). The result of a study on the prevalence of malnutrition in children under five years old in Salmas (in west of Iran) showed that the rate of stunting is 7.3% (8). The study of Davoodi et al. showed that the prevalence of stunting in Hamadan (in west of Iran) was 6% (31). Also, the study of Fesharakinia in Birjand city (in east of Iran) in 2011 showed that the prevalence of stunting in under 5-year old children is 9.8% (33) . The study of Payandeh with the aim of determination of the prevalence of malnutrition among preschool children in northeast of Iran showed that the rate of stunting was 12.5% (10). Generally, as can be seen the prevalence of stunting in some regions of Iran is higher. Although, in recent years much efforts have been made to address deprivation such as economical, nutritional and social supporting, improvement quality of life, but there are still nutritional problems in these areas of Iran.
Use of various instruments for measurement of outcomes, inadequate sample size in some studies and various methods for sampling might have increased the risk of information bias and might have been a reason for high heterogeneity in the results of the included studies. In other words, these factors should be investigated in future studies.
The studies have shown that there are many different factors that contribute to child stunting, including poor maternal health and nutrition during pregnancy, anemia in women of reproductive age, child's inadequate nutrition (not eating enough or eating foods that lack growthpromoting nutrients), low birth weight, childhood overweight, exclusive breastfeeding, wasting, and recurrent infections or chronic or diseases which cause poor nutrient intake, absorption or utilization. Specifically, the maternal nutritional and health status before, during and after pregnancy influence child's early growth and development, beginning in the womb. For example, intrauterine growth restriction due to maternal undernutrition is responsible for 20% of childhood stunting (33,34). Therefore, for the prevention and control of childhood stunting all these factors must be considered.

Conclusion
In conclusion, it seems that the stunting indicates longterm malnutrition, and in the following years, with the help of adequate nutrition or greater care, education and improved living conditions it can not be reversed easily. So, growth monitoring and baby nutrition plans should be taken into consideration in order to reduce the prevalence of the stunting in Iran.