Weight disorders and anthropometric indices according to socioeconomic status of living place in Iranian children and adolescents: The CASPIAN-IV study.

BACKGROUND: Excess weight in children and adolescents is a multi-factorial phenomenon and associated with earlier risk of obesity-related diseases. This study aims to assess the prevalence of weight disorders and the mean values of anthropometric indices according to regional, socioeconomic, and urban-rural variations among Iranian children and adolescents.
MATERIALS AND METHODS: This nationwide study was performed in 2011-2012 among a representative multi-stage cluster sample of 14,880 Iranian students aged 6-8 years. The World Health Organization (WHO) reference curves were used to define weight disorders. Abdominal obesity was defined as the waist-to-height ratio (WHtR) of more than 0.5. Iran was classified into four regions according to the socioeconomic status (SES).
RESULTS: The mean (95% confidence interval) of body mass index (BMI), waist circumference (WC), and hip circumference (HC) was 18.8 (18.7, 18.9) kg/m(2), 67.0 (66.7, 67.3) cm, and 80.8 (80.3, 81.2) cm, respectively. The prevalence of underweight was 12.2%. A total of 9.7%, 11.9%, and 19.1% of students overweight, obese, and abdominally obese, respectively. The highest mean of BMI, WC, wrist circumference, HC, and WHtR were related to the second high SES (North-northeast) area (19.2 [18.8, 19.5], 68.3 [67.3, 69.4], 14.8 [14.7, 15.0], 82.6 [81.1, 84.0], and 0.464 [0.460, 0.468]). In contrast, the lowest SES (Southeast) region had the lowest mean of these anthropometric indices (17.6 [17.1, 18.2], 63.2 [61.7, 64.8], 14.5 [14.2, 14.8], 76.9 [74.9, 79.0], and 0.439 [0.434, 0.444]).
CONCLUSION: We found considerable differences in the prevalence of anthropometric measures throughout the country by SES of the region. Health policy making and implementing health strategies should consider SES of regions.

INTRODUCTION

Different patterns of weight disorders including underweight and excess weight are accompanied with increased risk of adverse health consequences in later life. Long-term impacts of such disorders have been emerged even after 55 years of follow-up in longitudinal studies.[12] The prevalence of childhood overweight and obesity has increased rapidly both in developed and developing countries; facing these populations with double burden of nutritional disorders.[3456] Childhood obesity has been recognized as a major public health crisis, due to the severe complications and the costly economic burden.[478] Thus, it highlights the necessity of implementing more effective monitoring programs for screening and prevention of such disorders.

The prevalence of childhood overweight and obesity is reported from 12% to more than 30% in developed countries, and from 2% to 12% in developing nations.[7] The high prevalence of obesity in Middle Eastern countries is of special concern. Iran as a developing country experiencing epidemiological and nutrition transition has a double burden of nutritional disorders and is now part of the world obesity epidemic.[910111213] A recent systematic review and meta-analysis revealed the increasing trend of overweight among Iranian young children with emphasize on providing the interventional preventive programs at national and regional levels.[14] Previous nationwide studies have documented a double burden of nutritional disorders in Iranian pediatric population, e.g., overweight (8.8%), obesity (4.5%), and underweight (13.9%) have been observed in the same population.[15]

Weight disorders are multi-factorial; socioeconomic status (SES) and geographic residence are of important determinants of such disorders.[16171819] Although, regional and Urban-rural disparities might contribute to the unevenly distributed prevalence of overweight and obesity, the role of SES and the residence area (urban vs. rural) have been relatively little addressed.

The aim of this study was to estimate the underweight, overweight, and obesity prevalence of Iranian children and adolescents, and to report the mean level of anthropometric indices based on SES, and living area at national and provincial levels.

MATERIALS AND METHODS

Study population and sampling framework

A detailed methodology of the study is reported elsewhere,[20] and herein we describe it in brief. This survey was conducted among 14,880 students, aged 6-18 years, and one of their parents living in urban and rural areas of 30 provinces in Iran. They were selected by multistage, cluster sampling method (48 clusters of 10 students in each province). In order to reach the favorite sample size, in each province; cluster sampling with same size clusters was applied. Stratification was performed in each province based on the residence area (urban/rural) and school grade (elementary/intermediate/high school). The sampling was proportional to size with equal sex ratio.

Iran was divided into four sub-national regions according to a previous study.[21] In order to determine sub-national regions; combination of two criteria (geography and SES using principal component analysis) was used. Some variables from the 2006 census, including literacy, family permanent income (family assets), and employment rate were used to calculate SES index. In this classification, the lowest SES was related to Southeast and the highest SES was related to central regions. North-northeast and west regions are in the middle, respectively.

Anthropometric measurements

Trained personnel according to standardized techniques measured height, weight, and waist circumference (WC) by using calibrated equipment. Weight was recorded to the nearest 0.1 kg in light clothing. Height was measured without shoes to the nearest 0.1 cm. For assessment of overweight and obesity, body mass index (BMI) was calculated as weight (kg) divided by height squared (m2). WC was measured to the nearest 0.1 cm with a nonelastic tape applied at a point midway between the lower border of the rib cage and the iliac crest at the end of normal expiration. Hip circumference (HC) was measured at the level of the greater trochanter to the nearest 0.1 cm. Wrist circumference was recorded on the dominant hand by a tape measure (to the nearest 0.1 cm). Students were asked to put their hands on a flat surface. The tape meter was not very tight or very loose. Waist-to-height ratio (WHtR) was obtained as WC (cm) divided by height (cm).

Definition of terms

The World Health Organization (WHO) growth curve was used to categorize BMI.[22] BMI was classified into underweight (BMI <5th percentile), normal weight (BMI between 5th and 85th percentiles), overweight (BMI between 85th and 95th percentiles), and obese (BMI ≥85th–95th percentiles). Abdominal obesity was defined WHtR >0.5.[23]

Statistical analysis

Mean of continuous variables are expressed with 95% confidence interval (CI). Prevalence of overweight, obesity, and abdominal obesity are presented with 95% CI across region and provinces. Mean and prevalence of anthropometric measure were compared across sex, region, living place, and province. Data were analyzed using survey data analysis methods in the STATA Corp. 2011 (Stata Statistical Software: Release 12, Stata Corp LP. Package, College Station, TX, USA). Figures were plotted R software (version 2.13.00; R Foundation for Statistical Computing, Vienna, Austria).

RESULTS

This national survey was conducted among 13,486 school students (6640 girls and 6846 boys) out of 14,880 invited subjects (response rate 90.6%) with a mean age of 12.47 (12.29, 12.64) years. A number of 10,191 of participants were from urban areas and 3295 from rural areas.

Overall, the mean (95%CI) height and weight of participants were 147.0 (146.5, 147.4) cm and 42.4 (42.0, 42.8) kg; respectively. The mean BMI, WC, and HC were 18.8 (18.7, 18.9) kg/m2, 67.0 (66.7, 67.3) cm, and 80.8 (80.3, 81.2) cm; respectively. The mean of WHtR and WC were 0.456 (0.454, 0.458) and 14.8 (14.7, 14.8) cm; respectively. The prevalence of underweight was 12.2% (11.5, 12.9). A total of 9.7% (9.1, 10.2) were overweight, and 11.9% (11.2, 12.6) were obese. Abdominal obesity was documented in 19.1% (18.2, 20.0) of students.

The mean values of anthropometric indices at national and regional level by sex and living place are shown in Table 1. In all regions, mean values of BMI, WC, HC, and WHtR were higher in urban than in rural residents, whereas, the highest mean of height and weight were in the highest SES (Central) region (147.9 [146.4, 149.3] and 43.5 [42.2, 44.8]; respectively) and second-high SES (North-Northeast) region (147.2 [145.3, 149.1] and 43.2 [41.5, 44.9] kg). In contrast, the lowest mean for these indices were related to lowest SES (Southeast) region (144.2 [141.2, 147.2] cm and 38.4 [35.9, 40.9], respectively). The highest mean of BMI, WC, wrist circumference, HC, and WHtR were related to second-high SES (North-Northeast) area (19.2 [18.8, 19.5], 68.3 [67.3, 69.4], 14.8 [14.7, 15.0], 82.6 [81.1, 84.0], and 0.464 [0.460, 0.468]). In contrast, the lowest SES (Southeast) region had the lowest mean of these anthropometric indices (17.6 [17.1, 18.2], 63.2 [61.7, 64.8], 14.5 [14.2, 14.8], 76.9 [74.9, 79.0], and 0.439 [0.434, 0.444]).

Table 1

The mean (95% CI) of anthropometric indices at national and regional level by sex and living place: The CASPIAN-IV study

Figure 1 and Appendix 1 show the mean ± standard error (SE) of anthropometric indices at the provincial level in Iranian children and adolescents.

Figure 1

(a-g) The mean ± standard error (SE) of anthropometric indices at provincial level. BMI = Body mass index, WC = Waist circumference, HC = Hip circumference; WHtR = Waist to height ratio

Appendix 1

The mean (95% CI) of anthropometric indices at provincial level by sex and living place: The CASPIAN-IV study

Table 2 shows the prevalence of weight disorders status at national and regional level by sex and living place. In all regions, the prevalence of underweight was higher in rural than in urban area, whereas, the prevalence of overweight, obesity, and abdominal obesity was higher in urban than in rural residents. The highest prevalence of overweight, obesity, and abdominal obesity were in second high SES (North-Northeast) (10.7% [9.5,12.1], 13.9% [12.4, 15.6], 23% [20.6, 25.6]) followed by the highest SES (Central) region (10.6% [9.5, 11.6], 13% [11.8, 14.3], 21% [19.4, 22.8]), and the lowest prevalence was in the lowest SES (Southeast) region (5.9% [4.5, 7.6], 6.3% [4.7, 8.4], 9.5% [7.6,12.0]). In contrast, the lowest SES (Southeast) region had the highest prevalence of underweight (21.9% [19.0, 25.0]), and second high SES (North-Northeast) area had the lowest prevalence (10.4% [8.5, 12.7]). Figure 2 and Appendix 2 show the prevalence of weight disorders and abdominal obesity at the provincial level in Iranian children and adolescents.

Table 2

The prevalence (95% CI) of weight disorders and abdominal obesity at national and regional level by sex and living place: The CASPIAN-IV study

Figure 2

(h-k) Prevalence of weight disorders at provincial level

Appendix 2

The prevalence (95% CI) of weight disorders and abdominal obesity at provincial level by sex and living place: The CASPIAN-IV study

DISCUSSION

The current study presents the prevalence of weight disorders and the mean anthropometric indices by SES, living area, and gender in a large representative sample of Iranian students. We found a higher frequency of overweight, obesity, and abdominal adiposity in the highest socioeconomic regions. By contrast, underweight was documented as the most prevalent weight disorder in regions with low SES.

In all four regions, urban residents had greater values of mean of BMI, WC, HC, and WHtR, while underweight was the prevailing disorder among rural inhabitants. The high prevalence of overweight and obesity might reflect an indicator of greater vulnerability of study population to the health co-morbidities associated with being overweight or obese. This finding is consistent with that of some earlier results reported among adult and adolescent population.[23242526]

It is well established that body weight status of an individual is affected by multiple underlying factors including a more complex interaction of environment and genetic. SES comprises the social environment, social norms, and media exposure, which could affect food preferences and consequently body weight.[27]

In the present study, we found that the distribution pattern in the prevalence of weight disorders was remarkably different by SES of the living region. We found higher values in the mean of anthropometric measures including BMI, WC, HC, and WHtR in urban than rural neighbors in all SES regions. By socioeconomic classification of Iran into four distinct regions, highest mean values were related to high SES districts. By contrast, the lowest mean anthropometric indices including BMI, WC, wrist, HC, and WHtR was documented in low SES region. Urban-rural disparities in odds of being an overweight or obese individual, illustrated by both BMI and WC, were highlighted in previous research, both in adult,[28] and pediatric population.[27] It could possibly be because of life style differences as urbanization accompanied with adherence to western-like diets and more sedentary activities.[2930]

In our study, the prevalence of overweight and obesity was at its highest level in high SES regions of the country and underweight was almost prevalent in rural than in urban areas. This finding is in line with some previous reports from the third national survey in China that the higher proportion of children with overweight and obesity were in geographic areas of Northern regions.[2431] Earlier studies have confirmed different patterns of overweight and obesity according to SES development.[3233] Higher SES position is less likely associated with childhood obesity in developed countries, whereas in developing nations as Indonesia, Brazil, and China children from households of higher SES are more likely to be obese compared to their lower SES counterparts.[343536] Various reasons as the local SES, process of industrialization, nutrition, physical activity, dietary habits, and the living condition might explain such differences.[33]

Furthermore, higher risk of stunting and underweight due to environmental conditions including food insecurity, lower access to healthy foods, inadequate nutrition, and health knowledge has been reported in previous studies.[37] Also, high prevalence of overweight and obesity might partly reflect the rapid changes in standards of living because of more urbanized industries, followed by epidemiologic and nutrition transition, and socioeconomic alterations.[3138]

Findings derived from the present study could be used to develop more effective health strategies, nutrition education and interventions for obesity prevention in the specific and diverse regions, SES, and urban vs. rural parts of the country.

This study has some limitations. First, the cross-sectional nature of the study does not allow us to conclude cause and effect relations. However, its nationwide representative sample might increase the generalizability of the results to urban-rural students across the country. In addition, we used measured data of anthropometric indices instead of self-reported measurements.

We found a considerable difference in the prevalence of anthropometric measures according to the SES of the region at national and sub-national levels. Higher income areas had more proportion of overweight, obese, and centrally obese children while underweight was more prevalent in low SES parts. These results emphasize the importance of SES development in the prevalence of anthropometric disorders and could probably help for implementing and designing nutrition and health education strategies specific to the SES of each geographic location.

AUTHOR'S CONTRIBUTIONS

RK and MB participated in study design and drafted the manuscript. RH and MQ participated in study design and statistical analysis and drafted the manuscript. MM contributed in study design. GA contributed in study design and drafted the manuscript. HA and TA contributed to the data acquisition and drafted the manuscript. AK and FN participated in study design and drafted the manuscript.