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Epidemiology

Sociodemographic disparity in the nutritional status among children and adolescents in Zhejiang Province

Abstract

Objective

To explore the sociodemographic disparity in the nutritional status including BMI, vitamin D and vitamin A status among children and adolescents in Zhejiang Province.

Methods

Weight, height serum 25-hydroxyvitamin D, and serum retinol were assessed in 2818 children and adolescents (6–17 years of age), using ten investigation sites in Zhejiang Province including urban and rural areas data from the China National Nutritional Study 2016–2017, which is a nationally representative cross-sectional study, to form provincial representative sample of Zhejiang Province. Sociodemographic disparity was explored.

Results

The prevalence of low weight, eutrophic, overweight and obese were 6.7%, 70.4%, 11.6%, and 11.2%, respectively. Significant difference was observed on BMI between males and females (P < 0.05), and between urban and rural areas (P < 0.05). The prevalence of vitamin D deficiency, inadequacy, normal and appropriate were 1.8%, 34.9%, 46.4% and 16.9%, respectively. Significant difference was observed on the concentration of 25‐hydroxyvitamin D (25(OH)D) both between genders and between living areas (P < 0.05). The prevalence of vitamin A deficiency, marginal deficiency and appropriate were 4.5%, 24.7%, and 70.9%, respectively. Significant difference was observed on the concentration of retinol between living area (P < 0.05).

Conclusions

Overweight and obesity, deficiency and inadequacy of vitamin D, deficiency and marginal deficiency of vitamin A were prevalent among children and adolescents. There were disparities between genders and between living areas on the nutritional status. Regional and sex-specific guidelines and public health policies for children and adolescent nutrition are needed.

Introduction

Childhood and adolescence are a critical period for physical development and learning knowledge, and nutrition status is crucial during this period. Obesity is a multifactorial condition and has also been described as a phenotype of numerous pathologies [1]. An article in lancet suggests that from 1979 to 2016, the number of obese girls has increased from 5 million to 50 million in 2016, and the number of obese boys has increased from 6 million to 76 million. In addition, 213 million children and adolescents are overweight, which is a precursor to obesity [2]. Similar to the increasing trend of childhood obesity and overweight in the world, with the transformation of China’s economic and social development, the nutritional and health status of students aged 6–17 has greatly improved, but they still face many nutritional problems, such as multiple forms of malnutrition (low body weight, overweight and obesity) and micronutrient deficiencies such as vitamin D and vitamin A. Vitamin D deficiency and insufficiency is a global health issue that afflicts more than one billion children and adults worldwide [3] and vitamin D deficiency may cause preeclampsia, childhood dental caries, periodontitis, autoimmune disorders, infectious diseases, cardiovascular disease, deadly cancers, type 2 diabetes and neurological disorders. Vitamin A deficiency recognized as a major public health nutrition issue in developing countries [4] and vitamin A play an important role for the cell function for growth, immunity and visual system. According to the systematic analysis for the Global Burden of Disease Study 2017, we learned that there is continuing disparity in mortality rates by sex across age groups [5]. Mia reported that observed sociodemographic and geographical inequalities imply slow progress in the overall improvement of both under- and overnutrition [6]. Sociodemographic disparity in the nutritional status remain an important issue for public health policy making. Nutritional status among children and adolescents needs to receive more careful attention because nutritional status of children and adolescents not only affects their health after adulthood, but also affects the establishment of lifelong healthy lifestyle. Based on these public nutrition issues that have not been taken seriously before, and limited information on nutritional complex status among children and adolescents in the recent years, this study intends to learn the nutritional status among children and adolescents in Zhejiang Province, and to analyze the sociodemographic disparity.

Methods

Study design

This study was based on data obtained from the China National Nutrition and Health Survey 2016–2017(CHNNS2016–2017). Our study chose children and adolescents from ten investigation sites in Zhejiang Province including urban and rural areas to form provincial representative sample of Zhejiang Province to access the nutritional status of students of 6–17 years old. In Zhejiang Province, the field investigation, physical examination and blood specimen collection was conducted between September 2016 and November 2017. Ethics approval was obtained from the Ethical Committee of Zhejiang Provincial Center for Disease Control and Prevention. All student guardian provided written informed consent after the research protocols were carefully explained to them. Thus, informed consents from the parents/guardians of all participants were received.

Sampling method and study population

This survey is part of the Chinese National Nutrition and Health Survey [7]. The China National Nutrition and Health Survey in 2016–2017 was a cross-sectional survey designed to examine the health and nutritional status of children and adolescents. A stratified multistage probability sampling design was used for the selection of participants. In Zhejiang Province, there were ten surveillance site representing urban and rural area of provincial coverage. The city is defined as the centre area of the big city as urban area, and the residential village is defined as a county as rural area. In every surveillance site, at least 280 children under 5 years old, 280 children and adolescents between 6 and 17 years old were interviewed. In this study, 2818 children and adolescents (6–17 years of age) were included in the analysis.

Measurements and data collection

Children’s sex and age were collected by general information questionnaire. Anthropometrical measurements were conducted by well-trained health workers of local community health centre who followed a reference protocol recommended by the WHO [8]. Height was measured without shoes to the nearest 0.2 cm using a portable stadiometer (TZG, Wuxi weighing instrument factory Co., Ltd, Wuxi, China), and weight was measured without shoes and in light clothing to the nearest 0.1 kg on a calibrated beam scale(G&G tc—200k, Shanghai taizhiheng electronic weighing instrument Co., Ltd, Shanghai, China). BMI was calculated by weight (kg)/height(m)2. According to “Screening for overweight and obesity among school-age children and adolescents” [9], overweight refers to a pre obesity state in which excessive fat accumulation in the body may cause health damage, and obesity is a kind of chronic metabolic disease, which is caused by the excessive accumulation of fat in the body, because the energy intake exceeds the energy consumption. We judged overweight and obesity of children aged 6–17 years old by BMI boundary values which are stratified by age. According to “Screening standard for malnutrition of school-age children and adolescents” [10], we judged low weight of children aged 6–17 years old by BMI boundary values, which are stratified by age. Blood samples were collected to detect the concentration of retinol, and we judged marginal deficiency and deficiency of vitamin A among children and adolescents by boundary values of serum retinol level [11]. Blood samples were collected to detect the concentration of 25‐hydroxyvitamin D (25(OH)D), and according to Standards recommended by the American Endocrine Association, we judged deficiency and inadequacy of vitamin D among children and adolescents by boundary values of the concentration of 25‐hydroxyvitamin D (25(OH)D) [12].

Statistical analysis

All the data were analyzed with SAS9.4(SAS Institute Inc, Cary, NC, USA). As continuous variables were not normally distributed, they were described as the median, 25th and 75th centiles. The differences between rural residents and urban residents were evaluated by nonparametric test (Mann–Whitney test). Bonferroni correction were used to perform the statistical adjustment for multiple comparisons. Category variables were evaluated with chi-square test. A two side P < 0.05 was utilized to assess statistical significance.

Results

Subject characteristics

Of the 2818 children and adolescents (6–17 years of age), there was 50.2% males. The prevalence of low weight, eutrophic, overweight and obese were 6.7%, 59.2%, 22.9% and 11.2%, respectively.

Nutritional status stratified by gender and living area

We classified the nutritional status as low weight, eutrophic, overweight and obese. According to “Screening for overweight and obesity among school-age children and adolescents”, we judged overweight and obesity. According to “Screening standard for malnutrition of school-age children and adolescents”, we judged low weight. The prevalence of overweight and obesity was 26.3% among males, higher than 19.4% among females (P < 0.05), and that was 26.6% among children and adolescents living in urban area, higher than those living in rural area (P < 0.05). The prevalence of obesity was 13.9% among males, higher than 8.6% among females (P < 0.05), and that was 13.5% among children and adolescents living in urban area, higher than those living in rural area (P < 0.05). The prevalence of low weight was higher in males than in females only in 12 age group (P < 0.05). But there was no significant difference of the prevalence of low weight between genders.

The median BMI of males and females was 17.79 and 17.35 kg/m2, and that of students living in urban area and rural area was 17.91 and 17.24 kg/m2. Significant difference was observed on BMI between males and females, and between urban and rural areas (P < 0.05). There was significant difference on BMI among different age (P = 0.000) (Table 1).

Table 1 BMI characteristics of children and adolescents stratified by age, gender and living area.

Vitamin D status stratified by gender and living area

The prevalence of vitamin D deficiency, inadequacy, normal and appropriate were 1.7%, 29.5%, 48.2% and 20.5% in males and 1.9%, 40.3%, 44.6% and 13.2% in females and that were 2.8%, 38.0%, 44.8% and 14.4% in urban area and 0.9%, 31.9%, 48% and 19.3% in rural area.

The median concentration of 25(OH)D of males and females was 23.23 and 21.43 mg/L, and that of students living in urban area and rural area was 21.62 and 22.89 mg/L. Significant difference was observed on the concentration of 25(OH)D both between genders and between living areas (P < 0.05). There was significant difference on the concentration of 25(OH)D among different age P = 0.000 (Table 2).

Table 2 Serum concentration of 25(OH)D among children and adolescents stratified by gender and living area.

Vitamin A status stratified by gender and living area

The prevalence of vitamin A deficiency, marginal deficiency, and appropriate were 5.2%, 25.3% and 69.4% in males and 3.7%, 24.0% and 72.3% in females, and that were 1.9%, 18.8% and 79.3% in urban area and 6.9%, 30.4% and 62.7% in rural area.

The median concentration of retinol of males and females was 0.34 and 0.35 ng/ml, and that of students living in urban area and rural area was 0.37 and 0.33 ng/ml. Significant difference was observed on the concentration of retinol between living area (P < 0.05), but there was no significant difference between genders (P > 0.05). There was significant difference on the concentration of retinol among different age (P = 0.000) (Table 3).

Table 3 Serum concentration of retinol among children and adolescents stratified by age, gender and living area.

Discussion

The present study illustrates the nutritional status using comparable data of the prevalence of obesity and overweight, vitamin D and vitamin A status in Zhejiang Province at the gender and living area level. We found that overweight, obesity, deficiency and inadequacy of vitamin D, deficiency and marginal deficiency of vitamin A were prevalent among children and adolescents. Disparities existed between genders and between living areas.

Better than previous investigations which were of small sample sizes and did not display detailed age-specific information about nutritional status, in this study, we found that the overall prevalence of overweight and obesity were 11.6% and 11.2% among children and adolescents in Zhejiang Province, higher than that of in Shandong Province and Jiangsu Province [13, 14], and higher than our previous study on children and adolescent [15]. The prevalence of overweight and obesity was 26.3% among males, higher than 19.4% among females, and this difference between genders is consistent with results from previous studies throughout China [16,17,18]. In most regions, the number of moderately and severely underweight children and adolescents decreased despite population growth [19]. In this study, the prevalence of low weight was 6.7% and there was no significant difference between genders. This result is consistent with results from previous studies in most countries [20]. Overweight was a greater problem in urban than rural areas [21, 22], and we found that the prevalence of overweight and obesity was 26.6% and 13.5% among children and adolescents living in urban area, higher than those living in rural area. But the United States, the prevalence of childhood obesity was low among youths living in households in the highest income families [23], and this contrasting suggests that in the period of economic transformation, the nutritional status of students in urban and rural areas is different. Although they have improved, but there is still a gap from the goal of reasonable diet.

Vitamin D plays a critical role in calcium and phosphate metabolism and helps maintain skeletal integrity in childhood, yet vitamin D status among children and adolescents is not optimistic. In our study, the prevalence of vitamin D deficiency, inadequacy, normal and appropriate were 1.8%, 34.9%, 46.4% and 16.9%, respectively. Similar with our study, a study carried out in southeastern China showed that older age groups were involved in increasing risk of vitamin D deficiency and insufficiency [24]. The data showed that vitamin D deficiency was very common among children and adolescents. The prevalence of vitamin D deficiency and inadequacy among females were higher than that of males, and this result is consistent with results of the result of nutrition survey in China, 2010–2012 [25], that the serum 25(OH)D concentration for males was higher than that of females. Another study in Canada suggested that children, who were older, obese, were less likely to be vitamin D sufficient [26].

Despite many of the countries lying within the tropics and subtropics, overcrowding, atmospheric pollution, a lack of vitamin D-fortified foods, and social customs that limit skin exposure to sunlight are major factors in the development of vitamin D deficiency [27]. Effective sun exposure should be encouraged and dietary vitamin D and vitamin D supplements are also recommended. Consumption of vitamin D-rich foods should be promoted among children and adolescents, and fortification of more food items or formal recommendations for vitamin D supplementation should be considered.

Vitamin A deficiency is a leading cause of preventable childhood blindness, and has been recognized as an important public health problem in many developing countries, according to China National Nutrition and Health Survey 2002 (CHNNS2002) and CHNNS2010–2013. The incidence of vitamin A deficiency in 10- to 13-year-old group was lower than that in 10- to 13-year-old group across areas and genders between 2002 and 2012. In 2012, the incidence of marginal vitamin A deficiency in the children was lower than that in 2002 [28]. However, vitamin A deficiency was still a moderate public health problem in Chinese children. The study in 2010–2012 found that the prevalence of vitamin A deficiency was 5.53%, and were 6. 14% in general rural areas and 4.55% in poverty rural areas, and the prevalence of marginal vitamin A deficiency was 18. 75%, and were 19. 17% in general rural areas and 18.07% in poverty rural areas, with no significant difference [29]. In our study, the prevalence of vitamin A deficiency was 4.5%, lower than the previous study of China, but the prevalence of marginal deficiency of vitamin A was 24.7%, higher than the previous study of China. Different from the previous study, our study also found the difference of the prevalence of vitamin A deficiency and marginal deficiency between urban and rural areas. Like the result of our study, a meta-analysis reported that in 2015, the prevalence of vitamin A deficiency and marginal deficiency was 5.16% and 24.29% in Chinese children aged 12 years and under. And this meta-analysis also suggested that rural children had a higher prevalence of vitamin A deficiency and marginal deficiency prevalence than urban children [30]. Our results suggest that children and adolescents especially those among rural areas should be considered an important population who were high-risk group for vitamin A deficiency.

Limitations of the present study should be noted. Family might be a clustering factor for these measures. Dependence among family members may be an issue for tests assuming sampling independence. But because of the policy of birth control of previous years in China, most of the respondents come from different families, and very few come from the same family. In addition, family information of the children and adolescents were not available in this study. The analysis of disparity of sociodemographic on nutritional status should be further explored in the future study.

Conclusions

In summary, the present study documented overweight and obesity, deficiency and inadequacy of vitamin D, deficiency and marginal deficiency of vitamin A were prevalent among children and adolescents. There were disparities between genders and between living areas on the nutritional status. Future public health strategies focused on the children and adolescents should consider the sociodemographic disparity.

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Acknowledgements

This work was supported by the National Key Research and Development Project (2018YFC1603103) and the Basic Public Welfare Research Plan of Zhejiang Province (LGF19H260002).

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YZ and RZ were responsible for the study design. YZ was responsible for data collection and analysis, paper writing and revision. LH, DS, MH, YF, DZ, WW and DH took part in the field investigation and data collection.

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Correspondence to Ronghua Zhang.

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Zou, Y., Zhang, R., Huang, L. et al. Sociodemographic disparity in the nutritional status among children and adolescents in Zhejiang Province. Eur J Clin Nutr 75, 307–313 (2021). https://doi.org/10.1038/s41430-020-00704-5

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