To our knowledge, this study provides the first evidence on the relationship between country-level prevalence of ECC, malnutrition, and anemia. However, not all types of malnutrition were associated with ECC. We found a positive and significant relationship between country-level prevalence of overweight and ECC in children 0-2-years of age, with higher prevalence of overweight associated with higher ECC prevalence. There was also an inverse relationship between country-level prevalence of anemia and ECC in 3-5-years olds with lower prevalence of anemia in countries with higher prevalence of ECC.
Overweight was associated with ECC only in children ≤ 2-years of age. The relationship between ECC, and childhood growth and development is not clear [5, 31]. The studies on the relationship between ECC and nutritional status provide conflicting results – some found no association [32-34], others found a positive association and some had inconclusive results [31, 35]. Recent Canadian studies reported that preschool children with severe ECC who were undergoing dental rehabilitation were more likely to have higher BMI z-scores than were caries-free controls [11, 12, 21, 23]. The inconsistent findings of the previous studies may be due to differences in the methods used for nutritional assessments, age range cut-offs, and confounders of dental caries, including differences in definition and severity of ECC [33].
The higher prevalence of overweight in countries with higher estimates of ECC in 0-2-year-olds may reflect the findings by El Tantawi et al. [26] who reported a higher prevalence of ECC in countries with greater economic growth. ECC and overweight/obesity share common risk factors – high frequency and quantity of free sugar consumption [36], food insecurity [37, 38], low socioeconomic status [39-41], residence in urban slums [42, 43] and rural areas [44, 45]. Growing economies are most likely to be undergoing nutrition transitions from traditional diets to low quality, processed, high-sugar, high-fat, carbohydrate-dense food and beverages that are poor in micronutrients [46, 47], which predisposes to overweight and high ECC prevalence. Our results might suggest that having ECC and being overweight have shared risk factors that are related to the macro-economic status of the country. A common risk factor approach [20, 48] may be used to address both ECC and overweight problems; with global action to control these health problems given priority to countries with greater economic growth.
The few studies that have assessed the relationship between ECC and nutritional status often included age ranges larger than that of ECC. Four studies conducted amongst preschool children, found no association between ECC and overweight in children 3 years of age [49], 2-5-year-olds [50], and 2-6-year-olds [51, 52]. These findings highlight the need for appropriate age groupings when studying ECC, as the relationship between ECC and nutritional status seems to be modulated by age. However, Davidson et al. [21] found that severe ECC was associated with obesity in 2-5-year-olds, thereby highlighting two additional dimensions to determining the association between ECC and overweight – the severity of ECC and the severity of overweight. Interestingly, those authors found an association between the two extremes of the phenomena studied. This finding also implies that enrolling children who have milder forms of caries and nutritional status may underestimate potential relationships [21]. Therefore, we suggest that future studies on ECC and nutritional status not only ensure that ECC is analyzed by age groups 0-2-year-olds and 3-5-year-olds, but also ensure that ECC and malnutrition data include the extremes of the variables, with emphasis on severe levels of ECC, such as those data using the World Health Organization Significant Caries Index. We exercise caution that the correlation we observed may be an artifact as correlational analysis at the macro-level is usually larger than it is for individuals [53].
Anemia, which is a complication of malnutrition and factors not malnutrition related [24, 36], was inversely associated with ECC in older preschool children. Anemia may not be a direct result of ECC, but it may be related to increased milk consumption in early childhood [23]. Evidence suggests that in developed countries where milk intake is high, the risk of anemia also is high [54, 55]. Anemia from high milk intakes results from early weaning of the child, and introduction of foods with low iron bioavailability. Milk also impairs non-heme and heme iron absorption [56]. Recent Canadian studies, a developed country that do not have malnutrition as a major health crisis [57] and have lower prevalence of ECC [58], reported that preschool children with severe ECC undergoing dental rehabilitation were more likely to have iron deficiency anemia than were caries-free controls [11, 12, 21, 23]. Future studies should explore this finding.
The present findings may have implications at the micro-level. Malnutrition is a complex disorder not solely caused by lack of food [59]. Feeding practices and other risk factors leading to malnutrition and/or anemia may be associated with greater risk for ECC. Health education programs to improve parental dietary choices and provision of sponsored healthful meals in kindergartens and similar gatherings may contribute to reducing the risk of these diseases but may not eliminate it. In addition, health providers who manage malnutrition, anemia and ECC could provide better and more comprehensive care to children by screening for either of the diseases and referring children to for specialized care. Structuring primary health care services to provide integrated dental and pediatric care may help address the dual burden of ECC and malnutrition. Dentists who care for patients with severe ECC should be aware that the children may have undiagnosed nutritional disease that warrants investigation.
One of the strengths of this study is that collated data on malnutrition included high-quality data from the Demographic Health Survey [60]. However, there is the risk of over-representation of children who have living mothers since the anthropometric variables used for assessment of nutritional status are only available for those who are alive: the sample may therefore have under-represented malnutrition in infants and preschool children [61, 62]. We controlled for gross national income per capita, but we could not control for all possible confounders, as these remain largely unknown due to lack of data. One of the confounders is sex, which plays a role in nutrition [63], but its role as a risk factor for ECC is unknown. We also were not able to adjust for possible confounders like sugar intake and oral hygiene status as country-level data for these variables were not available. Controlling for these factors may attenuate the relationships we established in this study. Our use of the z-scores adjusted for age and sex to determine nutritional status allowed for more meaningful reporting of means [21]. We did not use the body mass index to assess nutritional status because it is meant to be used in children ≥ 2 years of age whereas we focused on 2-year-olds and younger, in addition to children > 2 years of age.
A limitation of this study was use of the World Health Organization’s criteria for assessing caries by many of the epidemiological surveys [64]. This assessment tool does not include non-cavitated lesions: only 15% of ECC surveys reported non-cavitated and/or cavitated as the caries detection level [36]. The ECC prevalence for many countries may therefore be under-reported. Our study analysis was also limited by only a minor portion of the global ECC prevalence estimates being based on national surveys, which made generalizability of the study findings challenging. ECC is under-studied in many parts of the world and true population estimates are often unknown. Also, although we split the data on ECC into two age groups - 0-2 and 3-5-year-olds – estimates for wasting, stunting and overweight could not be split because the data were not available. Further, our study is cross-sectional, so the direction of the observed relationships cannot be ascertained i.e, whether ECC increases the risk of 0-2-year-old children being overweight, or being overweight increases the risk for ECC. A carefully designed longitudinal study may answer the questions this study have raised but were unanswered.