Systematic Literature Review of the Nutrient Status, Intake, and Diet Quality of Chinese Children across Different Age Groups

There is a lack of comprehensive reports on nutrient deficiencies and dietary intake among various age groups of children in China. The objective of this review is to provide an overview of the nutrient status, intake, and diet adequacy of Chinese children (0–18 years old). PubMed and Scopus were searched for literature published between January 2010 and July 2022. A systematic review approach with a quality assessment was performed to analyze 2986 identified articles in English and Chinese. Eighty-three articles were included in the analysis. In younger children, anemia and iron and Vitamin A deficiencies remain severe public health problems, despite high Vitamin A and adequate iron intake. In older children, a high prevalence of selenium; Vitamin A and D deficiencies; and inadequate intakes of Vitamins A, D, B, C, selenium, and calcium were reported. Intakes of dairy, soybeans, fruits, and vegetables were below recommended levels. High intakes of iodine, total and saturated fat, and sodium and low dietary diversity scores were also reported. As nutritional concerns vary with age and region, future nutrition interventions should be tailored accordingly.


Introduction
Malnutrition can have a significant and often irreversible adverse impact on a child's survival and growth, their ability to learn in school, and productivity in later life [1]. Failure to provide optimal nutrition can lead to malnutrition in the long term. The different forms of malnutrition are often referred to as a triple burden: undernutrition (underweight, stunting, and wasting), vitamin or mineral deficiencies, and overnutrition (overweight and obesity), resulting in diet-related non-communicable diseases [2].
China is the most populous country in the world, with approximately 1.4 billion people and one-fifth of the total number of children [3]. Recent decades of rapid socioeconomic development, urbanization, and modernization in China have greatly improved children's nutritional status [4]. There was a significant reduction in undernutrition and related mortality. China is one of the few countries on course to meet the nutrition-related targets for stunting and wasting under the Sustainable Development Goals (SDG) of the United Nations, and some progress has been made for low birth weight [5,6]. The rates of stunting were reduced by 70% (from 33.4% in 1990 to 9.9% in 2010) and underweight by 84% (from 19.1% to 3.6%) among Chinese children under 5 years. Similarly, stunting and underweight decreased in Chinese children and adolescents (7-12 years) from 2.4% in 2009 to 0.4% in 2011, and 24.6% in 2009 and 21.4% in 2011 [7,8].
In contrast, China has made no progress towards the SDG targets on the prevalence of overweight; instead, there has been a transition with the proportion of overweight children dren now exceeding the prevalence of undernutrition indicators. From 2000 to 20 rate of overweight and obesity among children 1-4 years increased from 9.5% and 11.9% and 6.9%, respectively [9]. In children and adolescents (7-12 years), the rate weight and obesity also increased, from 11.3% and 2.9% in 2009 to 12.6% and 6.3% [8]. In slightly older children and adolescents (6-17 years), the rate of overweig obesity increased from 9.0% and 7.2% in 2009 to 11.5% and 10.5% in 2011. The mos estimates in 2015 showed further increases of 11% and 12.7%, respectively [10].
Information on the nutritional status (e.g., stunting) of Chinese children is p available in reports by various organizations such as the United Nations Network trition (UNICEF, WHO, and FAO). Most of the data are derived from the Chin (Chinese Control and Prevention) and are based on its 2011-2013 and 2015-2017 Nutrition and Health Surveillance. However, a comprehensive report on nutrie ciencies and dietary inadequacies across various age groups and geographical area as readily available. It is hypothesized that due to the size of the country and rap nomic transition, there would be geographical differences across regions. Therefor from national studies, we have also included an overview of subnational studies, frequently provide more in-depth information for more limited geographical are objective of this paper is to provide an overview of the nutrient status, intake, a adequacy of Chinese children (0-18 years old) across various age groups and regi ing a systematic review approach.

Guidelines and Registration
This systematic review was conducted following PRISMA guidelines (Figure the study protocol registered under PROSPERO International Prospective Register tematic Reviews (registration number: CRD42020220110).  . PRISMA flow chart. * QATSDD score cut off reflected the third tertile for all the retrieved articles. Special weightage was given to criteria 5, 'Representative sample of target group of a reasonable size', whereby all observational studies with a maximum score (3) were included in the review regardless of the total QATSDD score.

Quality and Bias Assessment
Each of the four authors assessed the quality and bias of the included studies in one topic classification based on the 'Quality Assessment Tool for Reviewing Studies with Diverse Design' (QATSDD) [11]. These reviewers independently awarded each included paper quality scores by assessing each QATSDD criterion (for example, 'Description of the procedure for data collection') on a 4-point scale from 0 to 3 (0 = the criterion is not at all described, 1 = described to some extent, 2 = moderately described, and 3 = described in full). The resulting scores were then expressed as a percentage of the maximum possible score of 42. The sum of the scores for all relevant QATSDD criteria reflected the overall quality of each paper. The reviewing team decided to only include articles with a cutoff score of 26 or higher, which reflected the third tertile of the QATSDD score for all the retrieved articles. Special weightage was given to criteria 5, 'Representative sample of target group of a reasonable size', whereby all observational studies with a maximum score (3) were included in the review regardless of the total QATSDD score. This allowed all studies with large and representative sample sizes to be included in the review regardless of scoring on other quality criteria. The QATSDD assessment was then repeated by a different reviewer. In the case where the difference in scoring between reviewer #1 and reviewer #2 was larger than 4 points, a third reviewer further assessed the article.

Data Analysis
Data were then extracted and tabulated into standardized tables for nutrient status, nutrient intake, and food group intake (which included diet quality scores); outcome indicators are summarized in Table 1. A second reviewer repeated the data extraction on 5% of all full texts for quality purposes. For continuous outcomes with 3 or more data points (hemoglobin status, Vitamin A intake, and Vitamin D status), mean and standard errors (SEs) of the levels/intakes were pooled by meta-analysis and visualized using a forest plot in Stata version 17, 2021 (StataCorp LLC, College Station, TX, USA). For outcomes with different cutoffs across age groups (hemoglobin status and Vitamin A intake), pooled estimates were calculated within each age group. Subgroups other than age groups within the same study were combined to create a single study point for simplicity. If SEs were not reported, they were calculated or estimated from SDs, CIs, or pooled from studies reporting sufficient information. Inverse variance weighting was used to pool the different studies/publications. Results from the random-effects model were presented, considering the large between-study heterogeneity (quantified by the I2 statistic) in most cases.
Where 3 or fewer data points were available per age group, the data points were tabulated per nutrient or food group. The prevalence of nutrient deficiencies, insufficiencies, and inadequacies were reported based on cutoff levels used in the original articles (Table 1) be associated with subclinical functional deficits and/or enhanced risks of pathologies. Nutrient inadequacies refer to nutrient intakes below the recommended amount [12]. Mean nutrient intake values were reported and classified against the Chinese estimated average requirement (EAR) and Upper Limit (UL) [13]. Food intake was reported in g/day and % below recommendations (based on original article). Food group intake (g/day) was classified as adequate or inadequate based on the recommended daily intake from the Chinese Nutrition Society's Food Guide Pagoda [14]. Diet Quality was measured by scoring food patterns in terms of how closely they aligned with national dietary guidelines and how diverse the variety of choices was. The score was recorded, as was the scoring system used [15]. Prevalence of anemia: as per WHO guidelines, age-specific groups: for children <5 years <110 g/L anemia, for children aged 5-11 years <115 g/L anemia, for children aged 12-14 years <120 g/L anemia, for non-pregnant women (15 years and above) <120 g/L anemia, and for men (

Study Characteristics
A total of 202 eligible articles were identified from the literature search, of which 83 met the inclusion criteria for further analysis. Twenty-five studies (30%) were based on national surveys. However, these national studies do not cover all provinces in China. The remaining publications (n = 58, 70%) were subnational studies, mostly from western China (n = 28). Almost half of the studies (47%) included children from the general population (both rural and urban or unspecified), and around 47 studies (57%) included nutrient status indicators (Table 2).           5 Defined by consumption of at least 10 gs of 10 food groups. 6 Defined by consumption of at least 10 gs of 17 food groups. 7 The Healthy Diet Score included the following 5 components: fruits and vegetables ≥1/d; fish or fish products ≥2/wk; milk, bean, or dairy products ≥1/d; fried food/Western fast food ≤2/wk; sugar-sweetened beverages ≤2/wk. 8 The Chinese Children Dietary Index: 16 components, which incorporated nutrients, foods/food groups, and health-promoting behaviors.
The overall prevalence of anemia in rural settings ranged from 5.6 to 86%, and that in urban settings between 2.7% and 17%. Anemia prevalence in children aged 0-23 months in rural settings ranged from 17 to 86% and that in urban settings was between 6.3 and 17%, whereas children at 24-35 months in rural settings ranged from 5.6 to 42% and those in urban settings between 4.5 and 20% [52,53,[55][56][57]61,64,65,67,68,75,87,102,103,105]. In rural children aged 9, 12, and 14 years, the mean hemoglobin level was significantly lower (134.7 ± 12.6 g/L vs. 135.6 ± 13.0 g/L, p < 0.001) and the prevalence of anemia was significantly higher (8.9% vs. 8.0%, p < 0.01) compared with their urban peers. When analyzed stratified by sex and age, the difference between rural and urban anemia prevalence remained significant only in 12-and 14-year-old girls [47].
Similarly reported in the Nutrition Study of Pre-school Children and School Children, for children 3-11 years in seven cities and two villages across east, west, and central China, the prevalence of iron deficiency (ID), as measured by serum ferritin levels, significantly decreased with age (p < 0.001) [82].

Zinc Intake
Zinc inadequacy appears to increase with age. Data from CHNS 2011-12 showed children between 11 and 17 years had the highest prevalence of inadequacy, between 38 and 42%, followed by children aged 7-10 years at 28% and children 4-6 years at 24% [36]. CHNS 2015 reported that approximately 30% of children (6-17-year-old normal-weight children) had zinc inadequacy [28]. The MING study showed children between 0 and 6 months had a zinc inadequacy between 0.4 and 19% based on the type of feeding (breast and artificial, respectively) [63]. Further sub-national data are given in Table 4 [51,77,96,97].

Selenium Intake
Two studies reported selenium intake data from CHNS 2011-12. Lui et al., 2017 reported that children 6-11 years old had an overall median dietary selenium intake of 33.6 µg/day, and the prevalence of selenium inadequacy was 52% [22].  reported that for children 4-17 years, inadequacy ranged between 50.8 and 71.8%, which appeared to increase with age (Table 4) [36]. Hu et al., 2021 reported CHNS 2015 data showing approximately 65% selenium inadequacy in normal-weight boys and 70% in normal-weight girls (6-17 years) [28]. Tian et al. reported selenium intake of 70 µg/day (above the EAR (25-45 µg/day)) among 3-5-year-old children living in rural Hubei province. This, in combination with the selenium level in drinking water of 0.04µg/L, was suggested as an increased risk of toxicity [79], but not yet to the level of the UL between 100 and 150 µg/day.

Magnesium Intake
Magnesium intake in children (6 months-17 years) was reported in national studies, CHNS 2011-12 and CHNS 2015, and sub-national studies, between 113 and 2798 mg/day [28,42,62,77,84]. The CHNS 2015 study showed a rate between 50 and 60% magnesium inadequacy in normal-weight boys and girls (6-17 years) [28]. For all age groups, the mean magnesium intake was above the EAR, except for those 11 to 13 years.

Sodium Intake
Sodium intake in children (0-17 years) was reported to be between 67 and 6100 mg/day [36,39,42,62,63,77,97]. The prevalence of inadequacy was not reported for any age group. The mean sodium intake of younger children (0-11 months) was below the AI, and children from 1 to 17 years had a mean sodium intake above the AI and proposed intake for preventing non-communicable disease (PI-NCD) (

Iodine Status
Iodine deficiency prevalence, as measured by the presence of goiter in children (8-10 years), ranged from 2.2 to 14%, with 2.2% being the national average and 11-14% in Hebei province [46,100,106]. The median urinary iodine concentration (UIC) nationally for children (8-10 years) was less than 250 µg (227-239 µg/L nationally in 2011; 211 µg/L in Hebei, Guangxi and Zhejiang; and 191 µg/L in Zhejiang province) [45,46,86,100,106]. In Hebei, the median UIC was 419 µg/L; additionally, 68% of the study populations were > 300 µg/L, while this was 28% at the national level [46,100]. Two studies in Zhejiang province showed higher UIC in rural populations versus urban; however, this was not significant [86,101]. Pre-schoolers (3-6 years) had a median UIC of 181 µg/L for those living in rural areas and 182 µg/L for those living in urban areas; school-aged children (7-12 years) had a median of 191 µg/L for those living in rural areas and 166 µg/L for those living in urban areas; and adolescents (13-18 years old) had a median of 193 µg/L for those living in rural areas and 186 µg/L for those living in urban areas [86]. Similarly, in another study, children aged 8 years had UIC of 158 µg/l in rural areas and 161 µg/L in urban areas; children aged 9 years had 180 µg/L in rural areas and 157 µg/L in urban areas; and children aged 10 years had 185.4 µg/L in rural areas and 180 µg/L in urban areas [101].
No iodine intake data for children were found.
Yang C et al. used a higher cutoff of <30 µg/dL serum retinol concentration (same as VAI) than was used in other studies based on WHO criteria (<20 µg/dL serum retinol concentration), and reported a higher prevalence at 27% for children 7-17 years [32].
VAI appeared to peak in the 1-3-year-old group, between 43.3 and 54.1% [67,68,74], and to go down with age to approximately 14.32-21.13% (Table 5) [32,40,41,95,105]. One study by Wang et al. in central China reported a higher prevalence of VAD, namely 20% (VAI 41%) in children 0-12 years, compared with the CHNS studies mentioned above and other sub-national studies in western China [67,68,80,81,105]. In this study, VAD decreased with age; however, significance was not assessed, and no difference between sexes was found [74].  CHNS 2011-2012 data reported VAD among 6-17-year-old children. The reported prevalence of VAD was not significantly different between children in large cities (8.0%) vs. small-and medium-sized cities (7.6%) and between age groups for 6-11-year-old children (8.0%) vs. 12-17-year-old children (7.2%) [40]. The prevalence of VAI among children in large cities was 19% vs. small-and medium-sized cities (19%) and did not significantly differ. However, a significant difference was seen between 6-11-year-old children (17%) and 12-17-year-old children (21%) [40,41]. The prevalence of VAD in urban vs. rural Chinese children was also determined. However, no test of difference was performed. Children aged 6-9 years living in urban regions had a VAD of 10.7%, and those living in rural regions had a VAD of 8.9%. Children aged 10-13 years living in urban regions had a VAD prevalence of 7.6%, and those living in rural regions had a VAD prevalence of 5.7% [33]. A significant difference in VAD prevalence was reported for children of 6-17 years living in towns without high poverty levels (6.1%) vs. towns with high levels of poverty (4.6%) and for 6-11-year-old children (6.6%) vs. 12-17-year-old children (4.5%). The prevalence of VAI for children in towns without high levels of poverty was 19%, whereas this was 18% for children in towns with high poverty levels and 23% for 6-11-year-old children vs. 14% for 12-17-year-old children [41].

Vitamin B3 (Niacin) Intake
Vitamin B3 intake for children (0-17 years) was between 2.1 and 15.9 mg/day [42,50,62,63,84,97] (Table 5). The mean Vitamin B3 intake was above the AI and EAR for children 0-10 years old. The mean intake of Vitamin B3 from national data for children 11-17 years met the EAR; however, some sub-national values did not meet the EAR.
Vitamin B3 status information was not available.

Vitamin C Intake
Vitamin C intake for younger age groups (0-6 years) met the AI or EAR, whereas for older groups (7-17 years), mean intake from national and sub-national studies was lower than the EAR [36,42,50,62,63,84,97]. CHNS 2015 that reported approximately 65% of normal-weight children 6-17 years old had Vitamin C inadequacy [28]. The prevalence of Vitamin C inadequacy increased with age, as reported in the CHNS 2011-12 [36] (Table 5). Vitamin C status information was not available.

Vitamin D Intake
Vitamin D intake was reported in children 7-12 years old from The 2012 Nutrition Study of Pre-School children and School Children study at 1.1 μg/day, where the intake of 84% was below the EAR, 86% was below the RNI, and 8.9% was over the UL. The study showed that a higher quartile of Vitamin D intake was associated with a 16% reduction in the risk of Vitamin D deficiency (p < 0.001) [85].

Vitamin D Intake
Vitamin D intake was reported in children 7-12 years old from The 2012 Nutrition Study of Pre-School children and School Children study at 1.1 µg/day, where the intake of 84% was below the EAR, 86% was below the RNI, and 8.9% was over the UL. The study showed that a higher quartile of Vitamin D intake was associated with a 16% reduction in the risk of Vitamin D deficiency (p < 0.001) [85].

Vitamin B12 Status
There are limited studies on the prevalence of Vitamin B12 deficiency. Two studies located in west China reported that Vitamin B12 deficiency in children 6-35 months living in rural areas was between 0 and 20% [55,67]. In rural Huzhu county, Qinghai province, Vitamin B12 deficiency was reported at 0% in children 6-23 months of age [55], whereas in three counties with high levels of poverty (Wuding, Zhengan, and Zhenan) it was reported at 20% in children 12-35 months of age (347 ± 165 pg/mL) [67]. No dietary intake data were reported.

Folic acid Intake
Folic acid intake was reported in the MING study in eight urban cities of children 6-35 months and was reported to be above the AI and EAR [62].

Food Group Intake
The amount consumed (g/day) per food group and the percentage below recommendations are displayed in Table 6 and are defined across different age groups and geographical areas. Overall, the intake of milk and milk products was inadequate in 96-99% of children (3-8 years), and the mean intake was below the recommended amount (300 g/day) in all age groups [25,27,38,48,93,108]. Seafood intake was below national recommendations for children living in moderately urbanized and rural areas [38]. Intake of red meat and cereals, tubers, and legumes was above national recommendations for all groups, while for eggs, this was only the case for children living in highly and moderately urbanized areas [27,38,93,108]. All remaining (fruits, vegetables, and poultry) were within national recommendations. CHNS 2011-12 reported sugar-sweetened beverage intake at 2.84 ± 5.26 servings per day [44]. Table 6. Food group consumption of Chinese children (between 3 and 17 years) across general, highly urban, moderately urban, and rural areas. Recommendations are based on the 2016 Chinese Food Pagoda for general population of healthy people over 2 years of age.  [108]. c Calculated based on 5 g/day of soybeans, 21.5 g/day of beans, and 1.9 g/day of nuts (Cheng et al. (2016) sub-national study) [93]. d Grains = 217 g, tubers = 37 g, fried cereals = 23 g; children 12-17 years. e Chengdu (Cheng et al. (2016); sub-national study) [93].
Among older children, one study recommended adequate diet diversity, and based on national data of children aged 3-17 years, diet diversity was below the recommendation [53]. Another two studies showed a high proportion of the population not meeting recommendations, with only 8.7% of children 6-17 years meeting the 'Healthy Diet' Score based on The Chinese Child and Adolescent Cardiovascular Health (CCACH) study, and 20% of 9-15-year-old children meeting the dietary China Dietary Guidelines Index for Youth (CDGI-Y) score [43].

Discussion
As seen in the retrieved literature in this review, deficiencies of different vitamins and minerals were reported across various age groups. Anemia and iron deficiency remain severe public health problems in children below one year of age, while selenium deficiency was more frequent in older children. Both problems were frequently reported in western China. VAD remained severe for children of all ages based on national data, while VDD appeared to be less of a problem when abundant sunlight was available (in the summer and in south China).
Nutrient intakes in younger children did not seem to always match the nutrient deficiencies mentioned above. For example, Vitamin A intake was above recommended values, iron was adequate, and diet diversity scores were below recommended. Meanwhile, there was a high prevalence of VAD, VDD, and selenium deficiency in older children, matching the reported inadequacies. The intake of additional nutrients: calcium; magnesium; Vitamins B1, B2, and C; and food groups-dairy, soybeans, fruits, and vegetables-was also inadequate. Nevertheless, energy intake was below the recommendation, whereas fat and sodium intake were above the recommendation, suggesting an imbalanced diet.
Discrepancies between urban and rural areas seem to still exist, with some of the nutrient deficiencies such as Vitamin A, iron, and anemia being more prevalent in rural areas and towns with high poverty levels [33,40,41]. Additionally, children in rural areas tend to have less dietary diversity as than those in urban areas [83].
Causes of anemia can be multiple, with usually only half of the anemia cases attributable to iron deficiency and the other half to a lack of other hemopoietic nutrients (Vitamin B12, Vitamin A, and folic acid) or iron absorption enhancers (Vitamin C), infectious diseases, and genetic hemoglobin disorders [111]. Despite the limited number of publications on iron deficiency found in this review, the available data suggest that the majority of anemia cases (in one study, as high as 81%) in Chinese children may be due to iron deficiency [55]. Deficiencies in Vitamin B12 and folic acid were generally low and are unlikely to contribute much to the prevalence of anemia, whereas VAD remained high across all age groups and may contribute.
Globally, children under 5 years of age have the highest frequency of anemia [112]. A recent Lancet analysis in 2020 reported that 56% of preschool-age children (6-59 months) had at least one of the three core micronutrient deficiencies (iron, zinc, and Vitamin A). This was consistent with this review's finding of a higher prevalence of anemia, iron, and Vitamin A deficiency in younger aged children (no data were available in this review on zinc deficiency for children under 7 years old). The Lancet analysis reported a low prevalence of Vitamin B12 and folate deficiency from a limited number of countries; this was consistent with this review [113].
This review found that the highest anemia and ID prevalence were in children under 1 year old, especially from 6 to 12 months. It is recognized in the literature that at this age, during the complementary feeding phase, when foods are introduced to complement milk feeding, there is an increased risk of nutrient deficiencies, especially ID and IDA [114]. The prevalence of anemia in children under 6 months was found to be 46.1% in one study conducted in three national counties with high poverty levels. For the first 6 months of an infant's life, it is thought that most newborns have sufficient iron stored in their bodies. However, this is dependent on a number of factors, such as the mother having adequate iron stores during pregnancy, the baby being full-term, with normal birthweight, delayed umbilical cord clamping, and sufficient iron [115]. These factors were not given in this article; however, they may play a role in the high prevalence of ID in infants under 6 months found in this review. After 6 months, breastmilk is low in iron and body stores run out; iron-containing foods are important [115].
Exclusive breastfeeding was reported between 0.50 and 33.45% in 17 cities in China between 2005 and 2016 [115]. Due to the low number of articles included in this review on infants under 6 months of age, the impact of breastfeeding on the nutrient status of children could not be concluded. One study by MING et al. in 2014 showed the impact of breastfeeding, mixed feeding, and artificial feeding in the first 6 months on nutritional status and nutrient intake. Artificially fed children showed higher disease prevalence and lower Z scores of length-for-age, weight-for-age, and weight-for-length compared with those in breastfed infants. Mostly adequate nutrient intakes were found, except for Vitamin A and zinc, where many artificially fed infants were above the Upper Limit [63].
The prevalence of anemia in Chinese children was positively associated with anemia in mothers [67] and with monotonous diets [55], and was negatively associated with the consumption of meat [55], egg, and milk [47]. The consumption of animal-sourced foods, red meat, and eggs appears lower in the younger years of 0-29 months [55,61]. Animal food sources contain haem iron and retinol, which are both more bioavailable than the chemical forms of those nutrients found in plant foods. Furthermore, high cereal diets contain phytates which can additionally inhibit iron absorption [116]. Although iron and Vitamin A intake in younger children appear to be adequate, the bioavailability of these nutrients may be low. Additionally, the lower fat intake in children 0-3 years old, below the recommendation, could also reduce the availability of Vitamin A, as fat is needed to facilitate carotenoid absorption. The micronutrient deficiencies (Vitamins A and D, and selenium) and inadequacies (calcium; selenium; magnesium; Vitamins A, B1, B2, C, and D) in the diets of older children could be accounted for by low consumption of the following food groups: dairy, soybeans, seafood [93], nuts [108], fruits and vegetables [93,108], as well as diet diversity [42]. Vitamin D, calcium, and dairy are important nutrients and foods required for bone development in children. Infancy and childhood are important periods of life for bone development through the accrual of peak bone mass for skeletal maturity [117]. Poor bone health can have long-term adverse effects, such as osteoporosis in later life, which is of special concern in view of the ageing population of China [118]. The selenium content in soil is important to consider as a solution for selenium deficiency and intake inadequacies, as the selenium content of animal products, cereals, and plants can vary at least 10-fold based on the soil's selenium content [116]. It is important to consider the regional differences in selenium status, as Hebei province was at risk of toxicity.
Globally, obesity and overnutrition appear to be of increasing nutritional concern especially among older children [6]. In this review, total fat, saturated fat, and sodium intake were all reported as above recommended limits. It is important to limit the intake of these nutrients due to their contribution to obesity and risk for other non-communicable diseases, such as hypertension. It is likely that energy was under-reported in this review, given the increasing overweight and obesity prevalence in Chinese children and the reported energy being below the EER. Under-reporting is a common phenomenon in dietary intake assessment methods, especially in overweight and obese participants [119].
Several other nutrients and foods are also at risk of being overconsumed. It was reported that in some areas, such as in Hebei province, excess iodine levels were found for up to 68% of the population [100]. Salt, being one of the most important condiments in the Chinese diet, was used as an iodine fortification vehicle, enacted via legislation with the universal salt iodization act (USI) in 1995. Iodine intake is therefore linked to sodium intake from salt, which was shown to be consumed at higher than recommended levels across all age groups. Thus, the level of iodine in the salt might need to be revisited, as it may result in excessive iodine intake, leading to iodine-induced thyroid dysfunction. Drinking water from shallow wells may also have high iodine content and may expose people to high levels; this was found in eastern China [120].

Strength and Limitations
To the best of our knowledge, this is the first systematic review summarizing the available literature from the last 10 years on nutrient status, nutrient intake, food intake, and diet diversity in Chinese children 0 to 18 years of age. This review has several limitations, such as a lack of recent nutrient status and intake data at the national level. The latest national nutrient status data were collected in 2009 (not including anemia, which was last collected in 2014) for children 7 years and under and excluded calcium, folic acid, and Vitamin B12. National nutrient intake data for children 3 years and younger were missing, and thus we could only analyze sub-national or regional data. Additionally, national surveys, such as CHNS, do not cover all provinces of China. Sub-national studies, and in particular the data from baseline of intervention trials, which were included in the review, are in their nature limited in representativeness, containing lower subject numbers and frequently focusing on a specific group of interest. The prevalence of energy and nutrient adequacy was not always reported; therefore, the mean intake was assessed against several indicators, such as EAR, EAR, AI, %EI, and/or UL, depending on the reference values used in the individual study. These limitations do not allow accurate quantification of the inadequacy of intake. The adequacy of consumption of food groups and diet quality was even more difficult to assess, as the retrieved studies used a variety of scoring systems. A consistent approach to assessing the nutrient status and intake using the same food groups and scoring systems is warranted, especially in national studies.

Future Opportunities
Globally, there has been a shift in public health focus to move from nutrient to foodbased approaches. This is because of the multiple social, economic, and health benefits associated with successful food-based approaches that lead to year-round availability of, access to, and consumption of nutritionally adequate amounts and varieties of foods [121]. Additionally, poor dietary choices leave gaps in micronutrient intake and nutritional deficiencies still exist [122]. Even though food fortification programs in China have been successful in reducing many nutritional issues in recent decades [68,105,[123][124][125], it seems there are still pockets of nutritional deficits in specific age groups or regions that could require specific approaches. For example, a targeted food-based solution, focusing on specific food groups that were below recommended levels and nutrients that were deficient and/or inadequate, could be implemented. In older children, this could be dairy fortified with Vitamin A, Vitamin D, and/or selenium. For younger children, more bioavailable sources of Vitamin A and iron could be considered in terms of food fortification and supplementation. In addition, increasing dietary diversity can provide a more sustainable option to control malnutrition [126] and should be considered, especially in younger age groups, to develop lifelong healthy eating habits. Studies to assess the efficacy of these specific approaches need to be planned in the future.

Conclusions
Overall, anemia and iron deficiency remain key issues among the youngest age groups, especially in the western rural population of China. VAD remains of high concern in all age groups among Chinese children. Additionally, in older children, deficiencies in Vitamin D and selenium are nutritional issues. Nutrient inadequacies (iron; calcium; selenium; zinc; and Vitamins A, B1, B2, and C intake), in parallel with excess intake of total and saturated fat and sodium, tended to increase with age. The consumption of dairy, soybean, nuts, seafood, fruit and vegetables, and diet diversity could be increased, especially in younger children. Given various nutrition issues across age groups, seasons, and regions of China, nutrition interventions should be tailored to specific groups and geographically relevant areas.
Supplementary Materials: The following supporting information can be downloaded at: https://www. mdpi.com/article/10.3390/nu15061536/s1, Table S1: The mean carbohydrate intake range, reported from different studies across different age groups compared with EAR, %EI; Table S2: The mean protein intake range, reported from different studies across different age groups compared with RNI, EAR, and UL; Table S3: The mean phosphorus intake range, reported from different studies across different age groups compared with RNI, EAR, and UL.