A Case-Control Study of the Factors Associated with Anemia in Chinese Children Aged 3–7 years Old

Background Anemia in children is still an important public problem in China and can have a profound impact on the physical and mental health of children. The purpose of this study was to explore the risk factors for anemia among Chinese children aged 3–7 years old and to provide some basis for the prevention and control of anemia. Methods A matched case-control study was conducted and 1104 children (552 cases and 552 controls) were recruited in this study. Cases were children who were diagnosed with anemia by the doctor of physical examination and checked by one deputy chief physician of pediatrics, and controls were healthy children without anemia. Data were collected using a self-designed structured questionnaire. Univariable and multivariable analyses were used to identify independent determinants of anemia. P values less than 0.05 were used to declare statistical significance. Results In the multivariable analyses, maternal anemia before or during pregnancy and lactation (OR = 2.14, 95% CI: 1.10∼4.15; OR = 2.86, 95% CI: 1.66∼4.94; OR = 2.51, 95% CI: 1.13∼5.60), gestational weeks (OR = 0.72, 95% CI: 0.53∼0.96), having G6PD deficiency or thalassemia (OR = 8.12, 95% CI: 2.00∼33.04; OR = 36.25, 95% CI: 10.40∼126.43), having cold and cough in previous two weeks (OR = 1.56, 95% CI: 1.04∼2.34), family income (OR = 0.80, 95% CI: 0.65∼0.97), and being a picky eater (OR = 1.80, 95% CI: 1.20∼2.71) were determinants of anemia in children aged 3–7 years old. Conclusions Some of the identified factors are modifiable and could be targeted to reduce childhood anemia. More emphasis should be given by the concerned bodies to intervene in the anemia problem by improving the maternal health education, screening for disease-related anemia, requesting medical services in a timely manner, improving the economic status of households, promoting dietary habits, and improving sanitation and hygiene practices.


Introduction
Anemia is regarded as a decrease in the number of red blood cells or their oxygen-carrying capacity. It is also defned as a hemoglobin level below 11 mg/dl for children 6 to 59 months of age [1]. Childhood anemia is a major public health problem worldwide afecting both developing and developed countries [2]. It is associated with adverse efects including impaired immunity and, cognitive development and reduce capacity for work [3][4][5].
Te causes of anemia are multifactorial, including shortage of hematopoietic materials [11]. Some reviews have reported the factors related to anemia, such as poor dietary diversity, food insecurity, deworming, maternal anemia, gastrointestinal disease, and educational status [12,13].
Children are deemed to be at greater risk than other populations [14]. Over the recent years, more attention has been on children. However, many studies related to anemia in children have been cross-sectional, and few analytical studies have been reported. Pingshan is one district of Shenzhen municipality located in the northeast. Te economic level is relatively lower, and the migrant population is relatively large. Implementing concrete strategies to reduce is a major task. Terefore, it is important to identify the associated factors to address the problem. To explore factors related to anemia in children, a case-control study was conducted, which could provide support for future anemia prevention and control measures.

Study Design and Participants.
A case-control study was conducted from 2018 to 2020 among children aged 3-7 years old in all kindergartens of Pingshan District, Shenzhen. Every child received physical examination and blood tests at least once a year. All children identifed as having anemia by physical examination and HemoCue were included in the casecontrol study as cases. Ten healthy children without anemia were selected as controls from the same class. A case/control rate of 1 :1 was applied. Te matching conditions were the same sex and an age diference of less than 3 months. Te sample size was determined by the software of PASS. Assuming a proportion of exposure in cases was 12.0%, a power of 80% and 5% of signifcance, and odds ratio being assumed to be 1.7, we required 528 cases and 528 controls (1 control per 1 case). In our study, we fnally included 552 cases and 552 controls.

Measurements.
Hemoglobin concentration of children was measured using the HemoCue. Te operational instructions were strictly obeyed and the outcomes were identifed by multiple researchers. Anemia was defned as hemoglobin <110 g/L for children under 59 months or <115 g/L for children over 5 years. Weight and height were measured for all children. Te height and weight of children were measured by intelligent physical examination instrument for children (Kangwa Intelligent physical examination instrument). Te scales were calibrated each morning and checked at regular intervals throughout the day. All measurements were made by a highly trained research anthropometrist. In addition, a repeated measurement for 10% of the children randomly selected each day was conducted. If the two measurements difered by more than 0.5 cm, a third measurement was taken. When the two measurements were similar, their mean was calculated. Weight-for-age (WAZ), height-for-age (HAZ), and BMI-for-age (BMIZ) z-scores were calculated using the World Health Organization Child Growth Standards Macro for SPSS. Underweight, stunting, and wasting were defned as WAZ < −2.0, HAZ < −2.0, and BMIZ < −2.0 standard deviations (SD), respectively.
2.3. Questionnaire. Self-designed structured questionnaires were administered to children's caregivers to obtain information. Te questionnaire's contents mainly included age, sex, ethnicity, birth status, maternal anemia condition, G6PD defciency, thalassemia, family status, and dietary habits. Trained interviewers conducted face-to-face interviews with the main caregivers. All caregivers participated on a voluntary basis and were not remunerated for their contribution.

Data Analysis.
Te information was recorded in a database using Excel. Te data was cleaned and analyzed using Stata 16.0. Simple frequencies and percentages were used for categorical variables. Univariable conditional logistic regression was used to determine the association of independent variables with the dependent variable. Using a manual stepwise forward selection of variables, signifcant variables were put in the multivariable conditional logistic models, one at a time, to check for signifcant association until a fnal model of signifcant variables was achieved. A P value equal to or less than 0.05 was considered statistically signifcant.

Ethics Approval and Consent to Participate
Tis study was approved by the Institutional Review Board (IRB) of Shenzhen Pingshan Maternal and Child Health Hospital and complied with the national legislation and the Declaration of Helsinki guidelines. Informed written consent was obtained from the caregivers who agreed to participate in this study, and their participation was voluntary.

Characteristics.
A total of 552 children and 552 controls were enrolled in the study. Tere were 55.62% (307/552) males and 44.38% (245/552) females in both the case group and the control group. Te mean ages for the cases and controls were 5.19 ± 0.80 years and 5.21 ± 0.79 years, respectively, and their age ranged between 3 and 7 years. Tere was no diference in the two matched variables including sex and age between the two groups. Greater than 90% of children, mothers, and fathers were of Han nationality in the two groups. Te mean ages of the mothers were 32.77 ± 4.26 years and 32.42 ± 4.73 years for the case and control groups. Te mean ages of the fathers were 34.86 ± 5.20 years and 32.99 ± 4.83 years for the case and control groups. More than 50% of children's parents had an educational level of senior high school or above in cases and controls (Table 1). Table 2 shows the results of univariable analysis conducted between anemia and each of the independent variables. Children in the East were likely to develop anemia than children in the West (OR � 1.86, 95% CI: 1.22∼2.86). Ethnic minority students and parents were prone to anemia compared with Han nationality (children: OR � 1.73, 95% CI: 1.02∼2.92; mother: OR � 1.76, 95% CI: 1.08∼2.88; father: OR � 1.92, 95% CI: 1.17∼3.14). Parents with higher education could decrease the risk of anemia in children ( Mothers' age, times of pregnancies, times of birth, mothers' consumption of tea during pregnancy, mode of delivery, diarrhea in recent weeks, trauma in the previous two weeks, permanent household population, consumption of dietary supplements containing iron, giving tea or milk to the children, cooking alone for the children, receiving childcare guidance, stunting, underweight, and wasting were not associated with anemia (p > 0.05).

Multivariable Analysis of Determinants of Anemia in
Children Aged 3-7 years Old. Te multivariable analysis (Table 3) identifed an association between maternal anemia before or during pregnancy and lactation and more children having anemia (before pregnancy: OR � 2.14, 95% CI:

Discussion
In China, the program for the development of children was implemented by the government and, has been working to solve the problem of anemia in children. Under this background, identifying the risk factors related to anemia is a very important task for eliminating anemia. Analytic   research, such as case-control studies, could provide more reliable predictors to guide the prevention and control of anemia in children.
Maternal anemia was consistently related to the occurrence of childhood anemia. Te study showed that children whose mothers had anemia before or during pregnancy and nursing period were more likely to develop anemia than those whose mothers did not have anemia during that time. Tis fnding was consistent with the results from Leite MS [15], as mothers and children were most often mutually exposed to a common set of physical, socioeconomic, and dietary conditions. Besides, Catherine Smith [16] suggested that maternal anemia would increase the risk of preterm birth. Children born prematurely have a higher risk of anemia in childhood. Similarly, we discovered that mothers with greater gestational weeks could decrease the risk of anemia in children.
We also found that genetic diseases, such as thalassemia and G6PD defciency, might increase the risk of anemia in children. In our study, children with thalassemia had the highest risk of developing anemia, with odds ratio of 34.26. Children with G6PD defciency also had an increased risk of anemia, with an odds ratio of 8.78. Similarly, a study from Philippe Joly [17] reported that these two kinds of genetic diseases were associated with children developing anemia. Because of enzyme genetic defciency or gene mutation, these two genetic diseases may lead to varying degrees of hemolysis in children, resulting in anemia.
In addition, we found that children with cold and cough in the previous two weeks were prone to anemia. Children with recurrent respiratory infections are more susceptible to anemia [18]. Terefore, when children develop respiratory symptoms such as colds and coughs, parents should seek medical services in a timely manner and take efective intervention measures to reduce the occurrence of adverse efects.
We also discovered that children's family economic level and living habits were important factors of infuencing anemia in children. In this study, the higher the family income was, the less likely children were to develop anemia. A similar study reported that the odds of children with a lower family income having iron defciency anemia were 3 times higher than those of children in the highest family income group [19]. Moreover, children who were picky eaters were prone to anemia. A meta-analysis also reported that poor food diversity was an important predictor of anemia in children under 5 [12]. Terefore, children with higher economic families might be more easily to acquire diversifed food, good health education, and develop good living habits that protect them from anemia.
Tere were some limitations to this study. First, we could not determine the prevalence of anemia, so we could not compare the status of subgroups. Second, some information bias may have occurred in this study because some data were obtained from past information. Tird, the factors associated with diferent types of anemia were not identifed in this study. Four, some variables (e.g., dietary intake) were not included because of the limited resources.

Conclusions
In this study, anemia was signifcantly associated with maternal anemia, gestational weeks, G6PD defciency, thalassemia, cold and cough in the previous two weeks, family income, and being a picky eater. Deeper knowledge about the etiology of anemia in this region is essential to its proper treatment and prevention.

Data Availability
Te data used to support the fndings of this study are available from the corresponding author upon request.

Conflicts of Interest
Te authors declare that they have no conficts of interests.