In the present study, we observed that more than half of studied children were stunted. Mentally retarded children were more affected compared with other children. Compared with children in the lowest category of dairy consumption, those in the highest category had lower odds of stunting. This association remained significant even after adjusting for covariates. In addition, moderate consumption of egg (1–3 time/wk) was inversely associated with stunting either before or after controlling for potential confounders. Such finding was also seen among mentally retarded children. No other significant association was seen between intakes of other food groups and stunting. To the best of our knowledge, this study is the first to assess the association between intakes of food groups and stunting in exceptional children.
Stunting is related to high morbidity during childhood and it’s consequence in adulthood [14]. This condition can increase risk of overweight, obesity and related diseases such as metabolic syndrome in adulthood [15, 14]. Furthermore, stunting in children can affect the cognitive status and also reduce work capacity [5, 16]. Diet has an important role in etiology of stunting. A large number of studies have assessed the association between dietary intakes and stunting [5, 17, 18]. However; less attention has been laid on exceptional children such as mentally retarded ones. Based on our findings, a significant inverse association was found between dairy consumption and stunting. In line with our findings, in a prospective cohort study, Nguyen et al. reported that consumption of dairy products was inversely associated with stunting [19]. In another cohort study, children who consumed higher amount of milk had better height growth, but consumption of other dairy products revealed no beneficial effect [20]. However, mentioned studies were conducted on healthy children, not exceptional ones. To our knowledge, we found no study assessing the association between dairy consumption and stunting in exceptional children.
Protein and calcium content of dairy may be a reason for the beneficial effects of this food group on height growth in children [21, 22]. A large number of studies have shown that calcium is involved in bone mineralization and longitudinal bone growth [23, 24]. Therefore, high intake of calcium may have role in prevention of stunting. In addition, dairy products are a rich source of high-quality proteins that are required for bone growth [23, 25]. These proteins can also stimulate the secretion of growth factors such as insulin-like growth factor 1 (IGF-1), known as contributing factor in linear growth of bone and mineralization [26]. In addition, children need more calcium and high-quality proteins (relative to weight) compared with adults because of rapid linear growth [27, 28]. Therefore, children who eat more dairy products, have higher bone and linear growth.
We also found that moderate intake of egg was inversely associated with stunting among exceptional children and also those who were mentally retarded. Some studies had shown similar findings in healthy children. In a clinical trial, it had been shown that children who consumed 10 eggs per week during 6 month had more linear growth compared with those who ate ≤ 1 egg per week [29]. Lee et al. reported [5] that consumption of egg in short stature children were significantly lower than those with normal height. In contrast, in a cross-sectional study on children in Ethiopia, Melaku et al. reported that adherence to a dietary pattern rich in egg was positively associated with stunting [30]. Assessing dietary pattern with high content of egg, not intake of egg alone, might be a reason for inconsistent results in Melaku et al. [30] study compared with present and previous studies. In addition, differences in previous findings might be explained by different processing and cooking of egg in different cultures.
The lack of significant inverse association between the highest category of egg consumption and stunting might be due to the low number of participants or cases of stunting in this category which can in turn result in the wide confidence intervals. Another reason might be cholesterol content of egg. Recently, it has been shown that total cholesterol levels in stunted children is higher than normal-height ones. Therefore, high intake of egg may stimulate stunting through elevation of total cholesterol concentrations.
Egg contains high biological value proteins that are required for skeletal and linear growth. In addition, egg is known as a rich source of choline and essential fatty acids. Choline as a precursor of phospholipids is required for growth and development [31]. Previous studies have shown that choline have a benefit for linear growth [32, 33]. For example, in a study on rural children, serum choline levels were lower in stunted children than those with normal height [33]. In addition, cell proliferation that is the first step of linear growth needs proteins, choline and essential fatty acids that are available in egg [32, 29, 34].
In the current study, we found that intakes of meat, fruits and vegetables were not associated with risk of stunting. This association remained non-significant even after adjustment for potential confounders. However, most previous studies showed an inverse association. Lee et al. reported that consumption of meat, fruits and vegetables in stunted children was lower than normal height ones [5]. These food groups contain antioxidants, different types of vitamins and minerals and also proteins which all are necessary for growth and development [10]. Different physical condition of children participated in the current study compared with those who participated in the earlier studies might be a reason for the lack of significant association between these food groups (meat, fruits and vegetables) and stunting in the current study. Chewing meat, fruits and vegetables for exceptional children particularly those who were mentally retarded might be more difficult than healthy children. In addition, energy intake of exceptional children might be low due to their physical condition and it is possible that beneficial effects of meat, fruits and vegetables intakes on height might occur in the range of required energy intake. However, we did not measure energy intake in the current study. It is suggested that future studies consider this important variable for diet-disease relationships in exceptional children.
Several limitations should be considered in the interpretation of current findings. Based on the cross-sectional design of our study, we cannot confer a causal link between intakes of food groups and stunting. Therefore, our findings should be confirmed by prospective studies. Although a validated questionnaire was used to assess dietary intakes in our study, the closed-end response nature of the questionnaire might increase the rate of misclassification. Although several confounders were adjusted for to assess the association between food groups intake and stunting, further controlling for other variables such as energy intake, parents’ height, economic status and physical activity might be needed to reach an independent association. Unfortunately, we did not collect data on these variables in the present study.
In conclusion, prevalence of stunting among exceptional children participated in the current study was high (50.6%). In terms of contributing factors, intakes of dairy products and egg were inversely associated with risk of stunting. However, intakes of other food groups including meat, fruits and vegetables were not significantly related to stunting.