Trend in the prevalence of metabolic phenotypes of obesity in Iranian children and adolescents: the CASPIAN (Childhood and Adolescence Surveillance and Prevention of Adult Non-communicable Disease) studies
Article information
Abstract
Purpose
Cardiometabolic risk factors can originate in childhood, especially in overweight individuals. In this study, we aimed to determine the trends in the prevalence of metabolic phenotypes among Iranian children and adolescents.
Methods
We determined the trends of the data from 3 nationwide school-based studies in Iran from 2003 to 2016 (the CASPIAN [Childhood and Adolescence Surveillance and Prevention of Adult Non-communicable Disease] studies). A total of 8,711 individuals (49.6% boys) aged 10–18 years were studied. Obesity and normal weight were considered as an age- and sex-specific body mass index > 95th percentile and between the 5th to 85th percentile, respectively. Metabolic syndrome (MetS) was defined according to the modified Adult Treatment Panel III criteria for children and adolescents. Children were categorized into 4 groups: metabolically healthy obesity (MHO), metabolically unhealthy obesity (MUO), metabolically healthy normal weight, and metabolically unhealthy normal weight (MUNW).
Results
Over 13 years, the prevalence of obesity increased significantly from 9.8% to 11.6% (p<0.001), whereas that of MetS did not change significantly (from 5.35% in 2003–2004 to 7.76% in 2009–2010 and 4.45% in 2015-2016, p=0.83). The prevalence of MHO increased significantly from 7.1% in 2004 to 9.6% in 2016 (p=0.005). However, the change in prevalence was not significant for MUO and MUNW.
Conclusions
From 2003 to 2016, the prevalence of MetS and metabolic phenotypes except MHO did not change significantly among Iranian children. The marginal increase in MHO prevalence should be considered, as shifts from this phenotype to unhealthy phenotypes may influence the risk of developing noncommunicable diseases in adulthood.
Highlights
· Data from repeated nationwide, school-based surveys conducted in Iran between 2003 and 2016 were used to assess trends in metabolic phenotypes among children and adolescents.
· Childhood obesity increased significantly over time, while the prevalence of metabolic syndrome remained stable.
· Metabolically healthy obesity showed a modest but significant increase, underscoring the importance of early cardiometabolic prevention, as this phenotype may progress to metabolically unhealthy states.
Introduction
In recent decades, the prevalence of weight disorders has increased among children and adolescents [1]. According to the World Health Organization (WHO), in 2022, more than 390 million children aged 5–19 years were overweight or obese [2]. According to a metaanalysis from 2001 to 2021, the prevalence of obesity among more than 2.5 million Iranian children was 11.4 % [3]. Another meta-analysis demonstrated that the prevalence of overweight and obesity among Iranian children up to 2022 was 12.4 % and 10.3 %, respectively [4]. There are associations between childhood obesity and cardiovascular diseases (CVDs) in adulthood. Obese children and adolescents are approximately 5 times more likely to remain obese in adulthood compared to their non-obese counterparts [5,6].
Despite the risk of various metabolic disorders among overweight and obese children, some of them are metabolically healthy. In this regard, the term "metabolically healthy obesity" (MHO) has been utilized in several investigations [7-9]. According to this concept, using anthropometrics and metabolic syndrome (MetS) parameters, individuals are categorized into 4 groups of MHO, metabolically unhealthy obese (MUO), metabolically healthy normal weight (MHNW), and metabolically unhealthy normal weight (MUNW) [8]. Compared to the MHNW, MHO cases are at higher risk of converting to MUO and developing noncommunicable diseases (NCDs). Thus, preventive interventions should be focused on MHO subjects [10]. Various studies have shown that the increased risk of NCDs in individuals with MUO compared to MHO was due to distribution and function of adipose tissue [11,12]. Individuals with MUO have lower subcutaneous fat, higher visceral fat, and greater fat accumulation in hepatic and muscular tissues compared to the MHO cases. These factors contribute to insulin resistance in MUO individuals [13].
Studies have assessed the prevalence of metabolic phenotypes among children and adolescents in different regions and reported various findings [14-16]. This might be due to differences in criteria for defining metabolic phenotypes, the age range of the participants, and genetic differences. However, there are limited studies regarding the trends in the prevalence of metabolic phenotypes. A multisection cross-sectional survey of South Korean youths demonstrated that the prevalence of MHO did not change significantly between 2011 and 2019. However, the prevalence of overweight and obesity increased significantly during this period [17]. On the other hand, a serial investigation among US adolescents showed a significant increase in MHO prevalence [18].
Investigation of the trends of metabolic phenotypes among children and adolescents in a community reflects the impact of health interventions over time and shows a path for further preventive interventions. In addition, implementing appropriate preventive measures during childhood could diminish the burden of NCDs in adulthood. However, no longitudinal or repeated surveys have investigated the changes in metabolic phenotypes in Iranian children and adolescents. In the present study, we examined the trends of prevalence of metabolic phenotypes of obesity in Iranian children and adolescents over a span of 13 years.
Materials and methods
1. Study design and patients
This study was performed using data obtained from the "Childhood and Adolescence Surveillance and Prevention of Adult Non-communicable Disease (CASPIAN) studies" of Iranian children and adolescents. These multisection cross-sectional investigations were conducted in 30 provinces of Iran and assessed the possible risk factors for NCDs. Data of Iranian children and adolescents were gathered through CASPIAN I (2003– 2004), CASPIAN-III (2009–2010), and CASPIAN V (2015– 2016). Detailed information on the survey design and methods of each survey has been published previously [19-21]. The protocol of the current study was approved by the ethical committee of Isfahan University of Medical Sciences (IR.MUI.MED.REC.1402.162).
The data were collected via interviews; questionnaires completed by children and their parents; and measurement of biochemical parameters in blood samples, anthropometric features, and blood pressure (BP). CASPIAN-I was performed from 2003 to 2004 in 23 provinces of Iran. The sample size was 21,111 children and adolescents aged 6–18 years. Anthropometrics and BP were evaluated in all participants, and biochemical parameters were measured in 4811 participants [19]. CASPIAN-III was conducted between 2009–2010 in 27 provinces of Iran. The total sample size was 5,528 students aged 10–18 years [20]. CASPIAN-V was performed in 2015–2016 among 14,400 students aged 7–18 years. Blood samples and biochemical items were collected from 4,200 participants [21]. The flowchart of participant inclusion is shown in Fig. 1. After explaining the aim and objectives of the investigation, written and verbal consent was obtained from both participants and their parents.
Study flowchart of included participants. CASPIAN, Childhood and Adolescence Surveillance and Prevention of Adult Non-communicable Disease; BMI, body mass index; WC, waist circumference; TG, triglycerides; HDL-C, high-density lipoprotein cholesterol; FBS, fasting blood sugar; BP, blood pressure.
2. Physical measurements
A team of qualified healthcare providers conducted the physical examination following established protocols and utilizing calibrated instruments. Weight was recorded in light clothing to the nearest 0.1 kg using a SECA digital weighing scale (SECA, Germany). Height was measured without shoes to the nearest 0.1 cm while the participants stood with their shoulders in a natural position [22]. Body mass index (BMI) was determined by dividing weight in kilograms by the square of height in meters. The WHO growth charts were used to classify BMI [23]. Waist circumference (WC) was assessed with a nonelastic tape measure, positioned at a point equidistant from the lower edge of the rib cage and the iliac crest, after a normal expiration and was recorded to the nearest 0.1 cm. BP was assessed on the right arm with the participant in a seated position utilizing a mercury sphygmomanometer equipped with a suitable cuff size. Measurements were performed twice at 5-minute intervals. Both systolic and diastolic BPs were documented, and the average value was calculated [24].
3. Laboratory data
Following a 12-hour overnight fasting period, a 6-mL venous blood sample was obtained from eligible participants. All collection tubes underwent centrifugation at 2,500–3,000 g for 10 minutes. Immediately postcentrifugation, serum samples were divided into 200-μL aliquots and preserved at -70°C. Utilizing a cold chain protocol, all samples were transported to the Isfahan Mahdieh Laboratory. Fasting blood sugar (FBS), triglyceride (TG), total cholesterol, low-density lipoprotein cholesterol, and high-density lipoprotein cholesterol (HDL-C) levels were determined enzymatically using a Hitachi auto-analyzer (Tokyo, Japan).
4. Definitions
All participants regardless of CASPIAN phase were categorized into 4 groups based on obese or normal weight and metabolically healthy or unhealthy. According to the WHO growth curve, general obesity is defined as a BMI higher than the 95th age- and sex-specific percentile. Normal weight is a BMI between the 5th to 85th percentiles for age and sex [23]. MetS was defined according to the modified Adult Treatment Panel III criteria for children and adolescents [25]. FBS greater than 110 mg/dL, fasting serum TG higher than 110 mg/dL, serum HDL-C less than 40 mg/dL, hypertension (systolic or diastolic BP higher than 90th age-, sex-, and height-specific percentile) [26], and abdominal obesity (WC greater than the 90th age- and sex-specific percentile) are considered as the parameters of MetS. If a person had 3 of the 5 parameters, the participant was categorized as metabolically unhealthy. According to these criteria, participants were categorized into 4 groups of MHO, MUO, MHNW, and MUNW.
5. Statistical analysis
Analyses were based on complete case data. Descriptive statistics were reported for each CASPIAN phase. Categorical variables were expressed as frequencies and percentages. Comparisons across the 3 survey time points (CASPIAN-I: 2003–2004, CASPIAN-III: 2009–2010, CASPIAN-V: 2015–2016) were performed to identify trends in prevalence over time. To test for significant changes in prevalence, we used the Cochran-Armitage trend test for binary variables and Kendall's tau-c test for ordinal data. Chi-square tests were used where appropriate to assess differences in proportions between subgroups, such as sex. All trend analyses were stratified to explore sex-specific patterns, and results were presented separately for boys and girls. A 2-sided P-value <0.05 was considered statistically significant. No adjustments were performed for multiple comparisons due to the descriptive and exploratory nature of the study. Potential confounding factors were considered in interpretation but were not adjusted through multivariable modeling, given the focus on unadjusted trends over time in repeated cross-sectional surveys. All analyses were conducted using Stata 17.0 (StataCorp LLC, TX).
Results
Demographic characteristics of participants in each phase of the CASPIAN studies are presented in Table 1. Overall, 48% of participants in CASPIAN-V, 50.2% in CASPIAN-III, and 46.5% in CASPIAN-I were female. Table 1 and Fig. 2 also show the prevalence of MetS and its components among participants in each survey. The prevalence of MetS increased from 5.35% in CASPIAN-I to 7.76% in CASPIAN-III and then decreased to 4.45% in CASPIAN-V. According to Kendall’s tau-c test, the change was not significant (P=0.830). Regarding MetS components, the data show a significant increase in abdominal obesity over the timeline (8.32% to 14.11%, P<0.001), while the prevalence of hypertriglyceridemia (28.89% to 21.77%, P<0.001) and low HDL-C (41.67% to 30.95%, P<0.001) decreased significantly. The prevalence of high BP from 2002 to 2015 fluctuated, while the prevalence of high FBS significantly increased (0.91% to 4.46%, P<0.001). The prevalence of general obesity decreased from 9.8% in CASPIAN-I to 8.9% in CASPIANIII and then increased to 11.6% in CASPIAN-V. Overall, its prevalence significantly increased (P<0.001).
Prevalence of general obesity and MetS and its components among participants across 3 nationwide cross-sectional studies in Iran (CASPIAN studies)
Prevalence of MetS and its components among participants across 3 nationwide cross-sectional studies in Iran (CASPIAN studies). CASPIAN, Childhood and Adolescence Surveillance and Prevention of Adult Non-communicable Disease; FBS, fasting blood sugar; HDL-C, high-density lipoprotein cholesterol; BP, blood pressure; MetS, metabolic syndrome; TG, triglycerides; WC, waist circumference.
We also reported the prevalence of MetS and its components, as well as general obesity in each gender (Table 1). Among boys, the prevalence of general obesity increased from 9.6% (CASPIAN-I) to 10.1% (CASPIAN-III) and 12.6% (CASPIAN-V). However, its trend was not statistically significant (P=0.139). The prevalence of MetS significantly decreased among boys from 6.62% (CASPIAN-I) to 4.61% (CASPIAN-V) (P=0.022). As in the general population, the prevalence of hypertriglyceridemia and low HDL-C significantly decreased during the studied time period in both sexes (P=0.003 and P<0.001, respectively). Additionally, the prevalence of high FBS significantly increased in both girls and boys, the prevalence of high BP significantly decreased among boys (P=0.008), and the prevalence of abdominal obesity significantly increased among girls (P<0.001).
Table 2 shows the prevalence of the metabolic phenotypes over 13 years in both the general population and by sex. The prevalence of MUO and MUNW phenotypes increased from CASPIAN-I to CASPIAN-III, but a decrease occurred from CASPIAN-III to CASPIAN-V. The prevalence of MHO significantly increased from CASPIAN-I to CASPIAN-V (P=0.005), while the prevalence of MHNW significantly decreased (P=0.044) (Fig. 3).
Prevalence of metabolic phenotypes of obesity among participants across 3 nationwide cross-sectional studies in Iran (CASPIAN studies)
Prevalence of metabolic phenotypes across 3 nationwide cross-sectional studies in Iran (CASPIAN studies). CASPIAN, Childhood and Adolescence Surveillance and Prevention of Adult Non-communicable Disease; MUO, metabolically unhealthy obese; MUNW, metabolically unhealthy normal weight; MHO, metabolically healthy obese.
Discussion
According to nationwide studies in Iran, we observed a stationary trend in the prevalence of MetS, MUO, and MUNW phenotypes from 2003 to 2016. However, the prevalence of MHO indicated a marginal increase, and that of MHNW showed a marginal decrease during this time period. These results are similar to those of an investigation in Korea from 2011 to 2019 [17]. However, that study reported a not significant change in the prevalence of MHO (from 34.8% to 35.7%), with a considerably higher rate than that in our population. Another research among US adolescents aged 12–19 years indicated a significant increase in the prevalence of MHO from 13.2% to 16.4% during 1999–2018. As in our findings, the prevalence of MHNW showed a significant decrease from 68.1% to 61.7% among their population [18].
Additionally, a significant increase in the prevalence of abdominal obesity and high FBS and a significant decrease in those of hypertriglyceridemia and low HDL-C levels were observed in our population during this period. The prevalence of obesity increased in our study, which is consistent with the global increasing trend of obesity in youths [2,27]. This increase in the prevalence of obesity among Iranian children and adolescents might be attributed to shifts in lifestyle, which have led to greater accessibility to food and fastfood options, along with increased exposure to mass media and computer games among young people [3]. The WHO recommends that children and adolescents aged 5–17 years engage in a minimum of 60 minutes of moderate to vigorous physical exercise daily [28]. According to this criterion, 29.5% of Iranian girls and 20.5% of boys are considered physically active, highlighting that a large number of Iranian youths do not perform optimal levels of physical activity [29]. This sedentary behavior has resulted in various health complications that can persist into adulthood [30].
MHO refers to individuals with obesity without cardiometabolic disorders. The prevalence of MHO varies between regions, ranging from 7% to 87% [9,31,32]. This variation might be due to different definitions of MetS, genetic variations, and environmental factors. Individuals with MHO are at higher risk of transitioning to an unhealthy metabolic state [33] and have a higher risk of CVDs [34]. Therefore, recognizing MHO individuals, especially in early life, would help healthcare providers prevent progression of NCDs during adulthood. The MHO prevalence among Iranian youth was approximately 7.5% in 2003–2016, which is lower than in other investigations among Korean adolescents (39% in 2011–2019) [17], European youths (41.1% in 2014–2019) [32], United States adolescents (15.4% in 1999–2018) [18], and Canadian children (25% in 2010) [35]. Differences in lifestyle and environmental factors in addition to genetic predispositions can contribute to this variation [36]. However, differences in cutoff points used for MetS definitions and the year of investigation might affect the results, as temporal changes in environmental exposures, lifestyle patterns, and measurement tools can influence the observed prevalence. This increase in MHO should be addressed by the healthcare system, and measures should be taken to prevent unhealthy metabolic status.
The term MUNW or metabolically obese normal weight was first introduced by Ruderman et al. [37] in 1981 and refers to normal-weight individuals with metabolic abnormality. The presence of this phenotype among youths increases the risk of NCDs [38]. In all CASPIAN investigations, the prevalence of MUNW in adolescents was higher than that of MUO individuals. Therefore, even children with normal weight could be at risk for metabolic abnormalities, and repeated measurements of MetS components are pivotal [38].
This study provides the temporal trend of obesity of Iranian children and adolescents up to 2015 and also the changes in metabolic profile. To the best of our knowledge, this is the first investigation in Iran and the third across the world to determine the temporal trends of metabolic phenotypes of obesity among children and adolescents. In addition, the sample size of our study was much larger than in previous studies among Korean [17] and United States [18] youths. However, there are some limitations that should be considered. First is the decrease in activity required during the coronavirus disease 2019 pandemic [28]. Second, due to the multi– cross-sectional manner of this survey, we were unable to assess causal relations. Third, insufficient data on pubertal stage prevented us from distinguishing between prepubertal and pubertal participants. Future studies should aim to include detailed pubertal assessments to better understand how developmental stage influences the outcomes under investigation. Updated investigations are needed to clarify the changes in metabolic phenotypes over time. Further longitudinal studies would better clarify the transition rate between phenotypes.
In conclusion, according to multi–cross-sectional investigations among Iranian children and adolescents from 2003 to 2016, the prevalence of MetS and metabolic phenotypes other than MHO indicated a stationary trend. However, significant increase in abdominal obesity and high FBS and significant decrease in hypertriglyceridemia and low HDL-C levels were observed over the 13 studied years. Preventive interventions targeting children with MHO might decrease the burden of NCDs during adulthood.
Notes
Conflicts of interest
No potential conflict of interest relevant to this article was reported.
Funding
This study was conducted as project number 3402202, supported by Isfahan University of Medical Sciences. The funds allocated for conducting this project were received by Dr. Roya Kelishadi for the implementation of the study.
Data availability
The data that support the findings of this study can be provided by the corresponding author upon reasonable request.
Acknowledgments
This project was conducted using the data of 3 national school-based surveillance programs. The authors are thankful for the large team working on these national projects and for all the participants who cooperated with this study.
Author contribution
Conceptualization: SMT, MHB, MQ, MY, RK; Data curation: MY, RK; Funding acquisition: RK; Methodology: SMT, MHB, MQ, MY, RK; Project administration: MY, RK; Writing - original draft: SMT, MHB, MQ, MY; Writing - review & editing: SMT, MHB, MQ, MY, RK