INTRODUCTION

Changes and trends in growth indexes have been researched and reported in many studies in the recent decades. Especially, a positive weight and height trend in Iranian children and adolescents 2-18 year old was shown in the last decade of 20^th century by Hosseini et al.[1] However, the latest nationwide survey assessed the growth indexes percentiles of 2-18 year old Iranian children, has been conducted in 1997.[2] Since then, although several studies have been conducted in Iran, all of them were regional representative and did not stand for the whole nation.

In the year of 2000, Center of Disease Control (CDC) presented growth charts for the United States.[3, 4] Six years later, in the year of 2006, World Health Organization (WHO) released the result of an international multi-center study, which was implemented between 1997 and 2003 as WHO child growth standards.[5] The WHO study data is gathered from six countries (United States, Norway, Brazil, India, Oman, and Ghana), which is claimed to be representative for the whole world children.[6] Prior to 2004, 99 (68%) countries adopted the pervious National Center for Health Statistics or WHO references and 25 (17%) used their local standards.[7] However, currently, WHO 2006 growth standards are the main references in many countries, including Iran, to assess the growth status of the children.

Under or over nutrition is diagnosed using the growth standards. This emphasizes the importance of growth references and makes the assessment of newly updated growth references crucial. Many studies in both developed[8, 9] and developing[10, 11, 12, 13] countries have compared the international references with their own local data and suggest the use of local growth reference rather than international references such as WHO 2006 or CDC 2000. In addition, two studies[14, 15] have been recently conducted in two region of Iran, which showed the deviation of Iranian growth standards to the global ones.

Previous studies have shown that Iranian standard reference values of growth was lower than international references;[16] therefore, in this paper, in order to assess the present status of growth of Iranian infants and children, anthropometric indexes of Tehran's infants and children have been studied as it has been shown to be representative for the whole country.[17] Furthermore, to evaluate the efficiency of using such global standard references in Iranian population, the differences between current WHO growth standards and local charts have been addressed in this paper.

METHODS

RESULTS

Weight and height/length of 2107 infants and children aged 1 month to 6 years old were measured in 2010. Among, 1152 (54.7%) were male and 955 (45.3%) were female. Smooth standard references by age (years) and sex for weight, height or length, and BMI are given in Table 1. This table shows that the difference between girls and boys standards is more apparent for ages of 5 and 6 years and is slight for the first month of age. Grid tests for goodness of fit for the smooth weight (χ²_girls = 0.2, P > 0.999; χ²_boys = 0.4, P > 0.999), height (χ²_girls, _{0-2 years} = 5.3, P = 0.627; χ²_girls, _{2-6 years} = 5.1, P = 0.652; χ²_boys, _{0-2 years} = 11.0, P = 0.140; χ²_{boys, 2-6 years} = 10.9, P = 0.143), and BMI (χ² _{girls, 0-2 years} = 4.8, P = 0.688; χ²_{girls, 2-6 years} = 7.0, P = 0.432; χ²_{boys, 0-2 years} = 6.3, P = 0.507; χ²_{boys, 2-6 years} = 6.7, P = 0.465) curves were not significant. It confirms the goodness of fit of all growth curves to the data.

Table 1. Smooth standard reference values for weight, height, and BMI of Iranian children by age and sex

Figure 1 shows the standard values for weight of Iranian infants and children as well as the WHO standard references. Although, the lowest and median percentiles of weight for Iranian population seem to be close to WHO standards, higher centiles tend to diverge in boys for ages after 4 years. Annual increase of weight for Iranian girls and boys were on average 2.2 kg and 2.4 kg, respectively.

[Figure ID: F1] Figure 1. Weight centiles (5, 25, 50, 75, 95) of Iranian (a) girls and (b) boys (solid lines) compared to World Health Organization standards (dashed lines)

Standing height or recumbent length of Iranian infants and children is compared to WHO standards in Figure 2. A slight difference is apparent for 5^th and 95^th centiles between Iranian population and WHO curves; however, in total, it was not remarkable. For height, annual increment was 8.9 cm for both Iranian boys and girls.

[Figure ID: F2] Figure 2. Height centiles (5, 25, 50, 75, 95) of Iranian (a) girls and (b) boys (solid lines) compared to World Health Organization standards (dashed lines)

A considerable difference between BMI of Iranian infants and children and WHO standards is shown in Figure 3. Furthermore, the shape of BMI curves for Iranian boys and girls were not similar. In addition, it is visible that Adiposity Rebound (ADR); increase point in BMI after reaching the lowest point) for Iranian girls occur after the 6 years, but, it happens about the 3^rd year for boys.

[Figure ID: F3] Figure 3. Body mass index centiles (5, 25, 50, 75, 95) of Iranian (a) girls and (b) boys (solid lines) compared to World Health Organization standards (dashed lines)

DISCUSSION

The most interesting and important result in our work was the age at adiposity rebound for Iranian boys. Early ADR is suggested to be and an important risk factor for the adulthood obesity.[20] Previous study[16] has shown that ADR for both girls and boys of Iranian population was occurred about the age of 6 years, about two decades ago. Though in our analysis the age of ADR for girls showed to be after the age of 6 years, for boys it was shown that it will occur about the age of 3 years old.

Some studies have compared the BMI pattern for obese children with reference populations. In these studies, mean age at ADR showed to be about 3 for obese children and about 6 for the reference population.[21] Their results along with ours emphasize the importance of growth monitoring for Iranian boys and formulating policies to take appropriate preventive measures.

Another interesting result of our study was the change of BMI levels for Iranian boys after a decade. Hosseini et al.[16] compared the BMI levels of Iranian children and adolescents (2-18 years) to US population reference about two decades ago. Based on their results, BMI levels of Iranian children were considerably lower than US population for both boys and girls. Although, they did not investigate the levels for children younger than 2 years and also it was not compared to WHO reference standards, comparing their results together with ours implies the increment of levels for both Iranian girls and boys, which tends to be close to international references for girls, and even passes the reference standards for boys.

Emdadi et al.[15] have conducted the only recent similar work in North East in Iran, which is in contrast with ours. Although this study is recently carried out and has more subjects than ours, the different methodology is resulted in different shape and values for BMI standard references. In their study, the data from infants and children younger than 2 years is not measured. The methodology for constructing BMI standards suggested by WHO,[6] uses the data from children aged 18 months and older to obtain reference values for children older than 2 years. Having these data will play an important role in forming the shape of BMI reference curves.

BMI over 30 and 25 is defined as obesity and overweight for adults, respectively. However, there are no such criteria for children. Therefore, the extreme age and sex-specific centiles of BMI of national or international references are considered for diagnosing obesity or overweight in children.[22] Hence, in addition to above results, the reported centiles for BMI can be used for monitoring the nutritional and growth status of Iranian children.

Findings of a recent school-based nationwide study[23] showed that 15.5% of Iranian girls and 19.9% of Iranian boys aged 10-18 years were overweight or obese. On this study, overweight and obese were defined as having age and sex-specific BMI greater than +1 and +2 z-score based on WHO growth curves, respectively. Since near 15.9% of children of a normal population that follows WHO growth standards are overweight or obese, this study is consistent with ours, which shows that growth of Iranian girl are similar to international standards and BMI of Iranian boys are higher than WHO growth references.

In view of the fact that the BMI of Iranian children have increased during the recent years and adulthood obesity risk factor is now apparent, it is suggested to take the preventive measures such as the United States Preventive Services Task Force recommendations since it is shown that the prevalence of high BMI did not increase among children in United States during the year 2003-2006.[24]

Many studies have reported the growth of school-aged children, however, up to now no research has conducted the growth indexes of Iranian infants and children younger than 2 years. Beside this advantage of this study, we tried to have similar methodology with WHO to have comparable results; However, our study lacks from having longitudinal data. In addition, finding breast-fed children similar to WHO subjects was not easy to consider as an inclusion criterion. However, we measured the weight and height of healthy children to have similar subjects.

CONCLUSIONS

During two decades, BMI levels of Iranian infants and children increased noticeably and even BMI levels of Iranian boys currently passes the international references. Furthermore, age at adiposity rebound for Iranian boys was about 3 years, which is an important risk factor for obesity for later ages. In addition, smoothed centiles presented in this paper can be used as a tool for diagnosing obese infants and children of Iranian population.