The results of the National Survey reveal that more than half of indigenous children in Brazil presented anemia (51.2%) and approximately one-sixth presented moderate/severe anemia (16.4%). These results are similar in scale to those from the few existing epidemiological studies of anemia among indigenous children in Brazil, which highlighted the significance of this nutritional deficit in the epidemiological profile of members of localized communities, ethnic groups, and populations
According to the results of the National Survey, the prevalence rates of anemia in indigenous children nationally were approximately double those reported for non-indigenous Brazilian children in the same age group. According to the first nationwide survey assessing the occurrence of anemia in children < 5 years of age in Brazil, the National Survey on Demography and Health of Women and Children (Pesquisa Nacional de Demografia e Saúde da Criança e da Mulher – PNDS), which did not systematically include indigenous populations, the reported prevalence rates for anemia and moderate/severe anemia were 20.9% and 8.7%, respectively
. The pattern of inequality in the occurrence of anemia in indigenous and non-indigenous children in Brazil is also quite pronounced when comparing the frequencies observed among the four geopolitical regions of the country studied in the National Survey. The prevalence ratios of anemia among indigenous and non-indigenous children < 5 years were 1.6 in the Northeast, 4.7 in the Central-West, and 6.4 in the North. A prevalence ratio could not be calculated for the South/Southeast region because, whereas we combined the prevalence of anemia for these regions (48.0%), the PNDS presented them separately for the South (21.5%) and Southeast (22.6%) regions
The geographical distribution of anemia in indigenous children reveals prevalence rates to be highest in the North (66.4%), followed by the Central-West (51.5%), South/Southeast (48.0%), and Northeast (41.1%). This notable regional difference follows a similar pattern to that observed in the National Survey for other nutritional measures, such as the prevalence of chronic undernutrition among indigenous children
. Additionally, indigenous households in the North region were observed to have lower sanitation, maternal schooling, and socioeconomic indicators as compared to all other regions
. These findings suggest that nationwide generalizations about indicators of nutritional status in indigenous children in Brazil, such as anemia and undernutrition, can conceal important regional patterns.
The notable difference in the occurrence of anemia in indigenous and non-indigenous children in Brazil documented by the National Survey finds parallel in results from other countries. Khambalia et al.
 conducted a systematic review of the literature, identifying 50 studies published in English on the topic of anemia in indigenous peoples from 13 countries (Australia, Brazil, Canada, Guatemala, India, Kenya, Malaysia, Mexico, New Zealand, Sri Lanka, Tanzania, United States, and Venezuela). According to the authors, “the burden of anemia is overwhelmingly higher among indigenous groups compared to the general population and represents a moderate (20–39.9%) to severe (≥ 40%) public health problem”. Also according to these authors, anemia in indigenous children is most often preventable, being associated with the promotion of food security, improved living conditions and sanitation, and the treatment and prevention of parasitic diseases such as malaria and intestinal parasites.
Presently, about 300 indigenous ethnic groups, speakers of approximately 200 distinct languages, are identified in Brazil, constituting one of the national indigenous populations with the greatest ethnic diversity in the world
[23, 24]. Because these societies are socioculturally distinct from one another and from the national population, with heterogeneous forms of livelihood and social organization, the theoretical models of determination of diseases, including anemia, should be applied and interpreted with caution. Models such as those used in this paper are based in part on a set of variables, such as income and education, among others, which were originally derived from studies conducted in non-indigenous societies. Nevertheless, the use of such models for indigenous peoples in Brazil may be justified insofar as they increasingly participate in local and global markets, which in turn has important ramifications for their health, local economies, political systems, and social organizations, as is also occurring in other parts of the world
[25, 26]. Despite these caveats, the outcomes in the final models for anemia, which are discussed below, were associated with evaluated variables at all levels, as they are in many other studies on the epidemiology of childhood anemia.
The observed association between child’s age and anemia has been reported in several other studies worldwide
[27–29]. Children under two years of age experience high rates of growth, which increases the demand for micronutrients such as iron, folate, and vitamin B12. The introduction of foods with low iron levels during weaning and elevated frequencies of infectious and parasitic diseases among young children are also important factors in determining childhood anemia. However, the relationship between child’s sex and anemia is less consistent, with some studies indicating associations between these variables
[30, 31] and others not
[32–34]. The results of the National Survey point to an association between sex and anemia in indigenous children, with greater risk among boys, although the difference was small.
With regard to socioeconomic characteristics, the results of the National Survey indicate that both maternal schooling and the household goods index, which are often considered linked to family income, were shown to be protective factors for the occurrence of anemia in indigenous children in Brazil. As is well documented elsewhere, such dimensions are intimately related to the care received by children, including nourishment and access to health services
Concerning the physical and sanitation characteristics of households, several variables showed a protective effect against the occurrence of anemia, including type of flooring, type of roofing, and source of drinking water. The use of non-durable materials, generally of plant origin, in home construction is often interpreted in the international epidemiological literature as a reflection of unfavorable socioeconomic conditions. However, care must be taken in interpreting these results because the use of plant-based raw materials (e.g., wood or palm thatch) in indigenous communities in Brazil does not necessarily derive from monetary poverty and is often an essential component of traditional household architectural techniques, especially in rural areas
. Nevertheless, as previously indicated, indigenous peoples in Brazil are experiencing rapid environmental, sociocultural, and economic transformations with repercussions for the variables associated with anemia. Whereas in some parts of Brazil, especially the North region, traditional indigenous home construction techniques are widespread, in other parts of the country with longer and more widespread histories of economic development, industrialized materials often predominate
. This contrast suggests that at least in certain portions of Brazil, such as the South/Southeast and Northeast, the presence of traditional plant-based construction materials may indicate unfavorable socioeconomic conditions as is understood to be the case in other populations globally.
The findings of the National Survey indicate an unexpected association between anemia and domestic source of drinking water. Several studies point to the protective effect of piped water available for domestic consumption on the occurrence of anemia in Brazil and elsewhere
[40, 41]. However, the present study shows indigenous children living in households relying on drinking water from rivers and lakes to present lower rates of anemia than those in households with access to piped water. Potentially, these children may have greater access to nutrient-rich local foods than those living in household with piped water but relying on low-cost industrial foods. Analysis of this possibility is beyond the scope of the present paper and deserves further investigation.
Maternal anemia was consistently associated with the occurrence of child anemia. Mothers and children most often share a home environment, which involves mutual exposure to a common set of physical, socioeconomic, and dietary conditions. This association gains relevance when considering that the prevalence of anemia among indigenous women was 32.7%, which is also extremely high
[42–45]. Maternal iron deficiency is associated with low birth weight and prematurity, and there is evidence that even children born with adequate weight have diminished iron reserves when their mothers are anemic
[35, 46, 47].
Among the analyzed variables related to children, low height-for-age and low weight-for-age remained associated positively with anemia after controlling for other variables. The association between these anthropometric indices and anemia has also been observed in several other studies
[41, 48]. Nutritional status, as assessed by both anthropometry and hemoglobin levels, is affected by a common set of factors, including socioeconomic status, sanitation, infectious and parasitic diseases, and diet. With regard to diet, protein-energy malnutrition favors the development of anemia through a synergistic relationship. Moreover, low hemoglobin levels have been implicated in compromising linear growth
[49, 50]. It remains unclear why weight-for-height showed an inverse association in our sample. Other factors recognized as important in determining child anemia, such as gestational age at birth and birth order, were not investigated here due to the impossibility of obtaining reliable data from local indigenous health services and the limitations of our data, which were restricted to children < 5 years
Some limitations to this study should be taken into account when interpreting its results. The cross-sectional nature of the research design does not allow for the establishment of causal relationships. Moreover, the absence of data on infant feeding precludes analysis of dietary sources of bioavailable iron, which is important for understanding the epidemiology of anemia in the study population. The use of capillary blood instead of venous samples can constitute a source of bias due to the possibility of hemoglobin dilution with extracellular fluid through manipulation of the subject’s finger at the moment the technician pricks the skin and collects the blood drop. Nevertheless, this technique offers numerous widely recognized practical advantages and does not compromise the quality of diagnosis at the population level
[53, 54]. Additionally, the National Survey methodology did not address the etiology of anemia. This last point deserves particular attention because appropriate population treatment measures and intervention vary according to the disease’s etiology.
Iron deficiency is generally assumed to be the major cause of anemia globally
[1, 3]. In Brazil, dietary supplementation with iron sulfate for children between 6 and 18 months of age is a major nutritional initiative of the Ministry of Health that was implemented based on the assumption that most cases of anemia derive from dietary iron deficiency
. However, besides iron deficiency, other factors that may cause or be associated with anemia include nutritional deficiencies involving other micronutrients (e.g., folate, vitamin A, and vitamin B12), infectious and parasitic diseases (e.g., diarrhea, malaria, and geohelminthosis), glucose-6-phosphate dehydrogenase (G6PD) deficiency, and genetically derived hemoglobinopathies
[2, 27, 55]. Recent research in the western Amazonian region of Brazil indicate that about a third of anemia cases observed in a sample of non-indigenous children was not associated with iron deficiency
. Similarly, studies of children living in the South and Northeast regions of Brazil demonstrate that sizable rates of children suffer from anemia caused by other factors other than iron deficiency
Given this context, deeper knowledge about the etiology of anemia in indigenous children in Brazil is essential to its proper treatment and prevention. At present, there are no studies on nutritional deficiencies among indigenous populations in Brazil that measured serum folate, vitamin B12, plasma ferritin, or other micronutrients associated with anemia. Moreover, it is known that helminthiasis and diarrhea are highly prevalent in indigenous children in all regions of the country
[60–64] and that about 70% of Brazil’s indigenous population lives in regions with high risk for transmission of malaria, a parasitic disease that can be particularly acute during childhood and can cause severe anemia
[65–67]. Iron sulfate supplementation or treatment with standard dosages has low efficacy where there are high levels of infectious and parasitic diseases with the potential to impact nutritional status and, more specifically, to interfere directly on hemoglobin concentrations
In conclusion, the findings of the National Survey reported here show widespread occurrence of anemia among indigenous children in Brazil, with prevalence rates being substantially higher than those among non-indigenous children. The findings also point to regional differences in the prevalence of anemia among indigenous children, with the highest rate being observed in the North region of the country. Considering the serious consequences of anemia for child health and development, as well as the preventable nature of iron-deficiency anemia, it is necessary to develop control and prevention strategies that attend to the sociocultural and nutritional specificities of anemia in indigenous children in Brazil.