Association between Dietary Antioxidant Quality Score and Anthropometric Measurements in Children and Adolescents: The Weight Disorders Survey of the CASPIAN-IV Study

Abstract

INTRODUCTION

Prevalence of obesity and overweight among children and adolescents has increased significantly over the past few decades. Between 2011 and 2012, 9.7% of Iranian children and adolescents were overweight and 11.9% were obese [1]. Excess body weight in childhood is associated with increased risk for developing chronic diseases such as hypertension and diabetes in adulthood [2]. Obesity-associated inflammation and oxidative stress may be involved in the development of chronic conditions. Oxidative stress is characterized by the over-production of reactive oxygen species, which causes cell damage and consequent cardiovascular diseases, insulin resistance, diabetes mellitus and atherosclerosis [3]. It has been shown that anthropometric indices such as body mass index (BMI) are closely related to oxidative stress in adults, children and adolescents [4, 5]. Certain foods contain some antioxidants including vitamins A, C, E, zinc and selenium that protect cells against oxidative damage induced by free radicals [6]. Several studies have demonstrated an inverse relationship between dietary antioxidants intake and risk of cancer [7, 8]. Longer leukocyte telomere, a highly sensitive biomarker of oxidative damage, has been linked to dietary total antioxidant capacity (TAC) in Spanish children and adolescents [9]. However, few studies have investigated the impact of antioxidants intake on oxidative stress in obese pediatrics. It appears that dietary antioxidants play a preventive role against reduction of vitamin levels and antioxidant capacity in obese children and adolescents through regulation of pro-inflammatory cytokines expression [2]. It is not clear whether lower or higher dietary antioxidant intake is associated with obesity. To the best of our knowledge, limited experience exists on the relationship between anthropometric measures and dietary antioxidant intake among children and adolescents. Additionally, mostly single dietary antioxidant intake has been evaluated. The purpose of the present study was to investigate the association of dietary antioxidants intake and anthropometric measurements in Iranian children and adolescents.

MATERIALS AND METHODS

This nationwide cross-sectional study was performed within the framework of the Childhood and Adolescence Surveillance and PreventIon of Adult Noncommunicable disease (CASPIAN-IV). Detailed information about the study has been published previously [10]. In summary, this survey collected health-risk behaviors data from 4270 children and adolescent aged 6–18 years.

The study protocol was approved by the Ethics Committee of the Isfahan University of Medical Sciences and written informed consent was obtained from the participants.

Anthropometric assessment

Body weight was measured using a scale to ∼0.1 kg with light clothing and without shoes. Height was measured using a measuring tape to ∼0.1 centimeter without shoes. The BMI was defined as body weight (kg) divided by height squared (m²). The following cut-off points for age and gender was used for BMI classification: <5th percentile considered as underweight, between 5th and 85th percentiles considered as normal-weight and ≥85th percentile considered as overweight/obese [11]. Waist circumference (WC), hip circumference (HC), wrist circumference and neck circumference (NC) were measured with a flexible tape to ∼0.1 cm. Waist-to-hip ratio (WHR) was determined by dividing WC (in cm) by HC (in cm). Waist-to-height ratio (WHtR) was calculated as the ratio of WC (in cm) to height (in cm).

Physical activity assessment

Physical activity (PA) was evaluated by two questions: (i) during last week, how many days were you physically active for at least 30 min a day? The response options ranged from 0 to 7 days and (ii) on a regular basis, how much time do you spend in school physical education per week? PA <2 h/week was considered as low.

Dietary antioxidant quality score

Dietary intake data were obtained through a 168-item semi-quantitative food frequency questionnaire. This questionnaire was previously developed and validated [12]. Energy and nutrients intake was estimated using the Nutritionist IV software.

Dietary antioxidant quality score (DAQS) was calculated based on the daily dietary intake of selenium, zinc, vitamin A, vitamin C and vitamin E compared with daily recommended intake (DRI). This comparison was done for each of five mentioned nutrients and the following values were assigned: 0 if the intake was <2/3 of the DRI and 1 if the intake was >2/3 of the DRI. Total DAQS was achieved by adding the scores for five antioxidant nutrients with a range of 0 (very poor quality) to 5 (high quality) [13].

Statistical analysis

The results are represented as mean [standard deviation (SD)]. The normality of data was assessed graphically and using statistical tests. Comparisons between means of anthropometric measures and intakes of antioxidant nutrients in boys and girls were performed using independent Student’s t-test for normally distributed data and the Mann–Whitney test for non-normally distributed data. One-way ANOVA and Kruskal–Wallis tests were applied to compare intakes of antioxidant nutrients among groups of underweight, normal weight and overweight/obese for normal and non-normal distributions, respectively. The association between DAQs and anthropometric measurements, adjusted for age, gender, living area (rural or urban), energy intake and PA, was evaluated using multiple linear regression analysis. Statistical analyses were performed using statistical software STATA 12.0 (STATA Corp., College Station, TX, USA). p-Values <0.05 were considered as statistically significant.

RESULTS

The data for 4270 children and adolescents aged 6–18 years were eligible for the present study. Of the 4270 subjects studied, 52.6% were boys and 71.5% were urban. The mean (SD) age of boys was 11.26 (3.25) years, while that of girls was 11.57 (3.11) years. Table 1 shows the means (SD) of anthropometric measurements, age and PA by gender. The means of height, WC, NC, wrist circumference and PA in boys were significantly higher than girls (p < 0.05), whereas girls had significantly greater BMI and HC than boys (p < 0.05). Comparison of mean intakes of antioxidant nutrients by BMI status (underweight, normal-weight and overweight/obese) and gender are shown in Table 2. Underweight girls had significantly higher intakes of vitamin C and zinc than underweight boys. The intake of vitamin E was significantly more in normal-weight girls. Normal-weight boys had higher intakes of zinc and selenium than girls. Overweight/obese boys had higher selenium intake than overweight/obese girls. Totally, further intake of vitamin A, vitamin C, zinc and selenium was seen in overweight/obese children and adolescents (all p-values <0.001). The results of multiple regression analysis (Table 3) showed that DAQS adjusted for age, gender, living area (rural or urban), energy intake and PA was positively associated with WC, HC and WHtR in underweight children and adolescents (B = 1.614, 1.634 and 0.01, respectively; all ps < 0.05). Increased DAQS was significantly associated with higher WC and WHtR in normal–weight children and adolescents (B = 0.536 and 0.003, respectively; all ps < 0.05).

DISCUSSION

Our study showed significant differences in the dietary intake of antioxidant nutrients between weight categories. Mean intakes of vitamin A, vitamin C, zinc and selenium were highest in overweight/obese children and adolescents. There were some sex-differences in antioxidant intake of pediatrics. In under- and normal-weight children and adolescents, DAQS was positively related to WC and WHtR.

Inflammation was correlates closely with oxidative stress. It has shown that pro-inflammatory factors are predictors of the extent of oxidative stress [14]. As obesity is considered an inflammatory state [15], there are interrelationships among obesity, oxidative stress and inflammation [16]. Some of the inflammatory factors including fibrinogen, ferritin, IL-6 and TNF-α have been detected in overweight and obese children [17]. It has also been reported that weight loss might ameliorate circulating levels of oxidative stress biomarkers [18].

Oxidative stress could exacerbate obesity-related comorbidities including cardiovascular diseases and metabolic syndrome in adults [19]. There are possible reasons for the relationship between obesity and oxidative stress. Defective antioxidant defense system, lower concentration of antioxidants, increased lipid peroxidation and release of cytokines and adipokines from adipose tissue in obese compared with normal-weight individuals have been reported [20].

Lower level of antioxidants including carotenoids, vitamins E and C, zinc, magnesium and selenium was seen in obese individuals among age groups [21]. Similarly, Ortega, et al. [22] showed that obese children and adolescents had lower intake of antioxidants compared with controls. Puchau, et al. [23] showed that obese children and adolescents consumed less vitamins E and C compared with the controls. In contrast, our results suggested that overweight/obese children and adolescents had higher intakes of vitamin A, vitamin C, zinc and selenium. We previously reported that overweight/obese children and adolescents consumed more fruits than normal-weight children and adolescents [24]. This could justify higher intake of antioxidants in the present study. The reason could be attributed to higher energy intake in overweight/obese children and adolescents. These results do not mean that overweight/obese children and adolescents have lower oxidative stress.

An inverse association between BMI and dietary TAC has been found in children and adolescents [23]. Similarly, dietary TAC was negatively related to central adiposity measurements in healthy young adults [25]. Unexpectedly, our results do not support this hypothesis. We found that under- and normal-weight children and adolescents had higher WC and WHtR if their DAQS was greater. Null results have also been reported. No significant relationship between BMI and antioxidant intake was found in pre-to-early adolescent children [26]. Although some studies have demonstrated that fruit and vegetables are main sources of antioxidants [27] and its consumption is effective in reducing anthropometrics [28], a study on female softball players showed that WC increased when fruit and vegetable consumption rose after 11‐week nutrition curriculum with a technology component [29]. Increased intake of fruit and vegetables in primary school children was associated with increased weight, WC and WHR [30]. There are some conflicting findings as well. Higher serum α-tocopherol concentration has been positively associated with general and central obesity in adults [31]. There was no justification for these surprising findings in any of these studies and further investigation was suggested. The limitations of the present study are its cross-sectional design, possible biases of cross-sectional studies cannot be excluded, blood levels of antioxidants did not measured, potential interactions between the different dietary intakes was not assessed, dietary changes or lifetime dietary intake were not assessed, the lack of the culinary treatments data that might influence on the reported intake of antioxidants. However, representative study with large sample size, measuring NC and wrist circumference and adjusted data for relevant covariates known to affect anthropometric measurements are its strengths.

CONCLUSION

In this cross-sectional study, dietary intake of vitamin A, vitamin C, zinc and selenium was more in overweight/obese children and adolescents. DAQS was associated with some anthropometric measurements in under-weight and normal-weight children and adolescents. These findings suggest that DAQS may also be a potential marker of diet quality in under-weight and normal-weight subjects. It can provide a novel approach to assess the role of antioxidant intake on health promotion and diet-based therapies in under-weight and normal-weight children and adolescents.

FUNDING

This study was supported by Isfahan University of Medical Sciences.

REFERENCES