Adjustment for time-invariant and time-varying confounders in ‘unexplained residuals’ models for longitudinal data within a causal framework and associated challenges

‘Unexplained residuals’ models have been used within lifecourse epidemiology to model an exposure measured longitudinally at several time points in relation to a distal outcome. It has been claimed that these models have several advantages, including: the ability to estimate multiple total causal effects in a single model, and additional insight into the effect on the outcome of greater-than-expected increases in the exposure compared to traditional regression methods. We evaluate these properties and prove mathematically how adjustment for confounding variables must be made within this modelling framework. Importantly, we explicitly place unexplained residual models in a causal framework using directed acyclic graphs. This allows for theoretical justification of appropriate confounder adjustment and provides a framework for extending our results to more complex scenarios than those examined in this paper. We also discuss several interpretational issues relating to unexplained residual models within a causal framework. We argue that unexplained residual models offer no additional insights compared to traditional regression methods, and, in fact, are more challenging to implement; moreover, they artificially reduce estimated standard errors. Consequently, we conclude that unexplained residual models, if used, must be implemented with great care

Prevalence of anemia in children 6-59 months old in the state of Pernambuco, Brazil

Objective. To determine the prevalence of anemia in children 6-59 months old in Pernambuco, a state in northeastern Brazil, so as to help guide health and nutrition policies there. Methods. In 1997 a representative sample of 777 young children had their hemoglobin concentration measured. The sampling process was in three stages. First, 18 municipalities were randomly selected to represent the state and its three geographic areas (metropolitan region of Recife, urban interior, and rural interior). Next, using census lists, 45 census sectors were randomly chosen. Finally, 777 children aged 6-59 months old were selected. Blood was collected by venipuncture, and hemoglobin was measured with a portable hemoglobinometer. In the analysis, prevalence was weighted to reflect the census age distribution. Results. The prevalence of anemia among children 6-59 months old was 40.9% for the state as a whole. Prevalence in the metropolitan region of Recife was 39.6%, and it was 35.9% in the urban interior. The rural interior had the highest prevalence, 51.4%. Prevalence was twice as high in children aged 6-23 months as among those 24-59 months old, 61.8% vs. 31.0% (chi² = 77.9, P < 0.001). The mean hemoglobin concentrations in the younger and older age groups were 10.4 g/dL (standard deviation (SD) = 1.5) and 11.4 g/dL (SD = 1.4), respectively. There was no statistically significant difference between the sexes in terms of prevalence. Conclusions. This is the first statewide assessment of anemia prevalence among young children in Brazil. Given the very high prevalence of anemia among the children studied in Pernambuco, especially those in the age group of 6-23 months, public health interventions are needed

Desenvolvimento mental e motor aos 24 meses de crianças nascidas a termo com baixo peso Mental and motor development at 24 months of full-term low birthweight infants

Este estudo teve como objetivo comparar o desenvolvimento aos 24 meses de 152 crianças nascidas a termo, com baixo peso (< 2500g) e peso adequado (3000 a 3499g), pareadas numa proporção de 1:1 por sexo e idade. O desenvolvimento mental e motor foram avaliados pela escala de Bayley. Estudaram-se ainda algumas variáveis ambientais, como as condições sócio-econômicas e demográficas e a estimulação ambiental. As crianças do grupo de baixo peso ao nascer apresentaram, para os índices mental e motor, média significantemente mais baixa do que a do grupo de peso adequado (p<0,001) com diferença de 9,1 e 10,2 pontos, respectivamente. A análise de regressão linear múltipla evidenciou que as condições sócio-econômicas e de estimulação ambiental explicaram 11% e 12% da variação do índice de desenvolvimento mental e 12% e 9% do desenvolvimento motor, respectivamente. Juntas elas explicaram 23% e 21% da variação desses índices. O baixo peso ao nascer influenciou apenas 3% da variação do índice mental e 5% do motor.<br>The objective of this study was to compare the development at 24 months of 152 full-term infants, born with low (<2500g) and appropriate birth weight (3000 to 3499g), paired in a proportion of 1:1 by sex and age. Mental and motor development were assessed through the Bayley scale. A variety of sociodemographic and environmental stimulation conditions were also assessed. The infants born with low weight had on average significantly lower mental and motor indexes than those born with appropriate weight (p<0.001), with a difference of 9.1 and 10.2 points, respectively. The multiple linear regression analysis showed that socioeconomic conditions and environmental stimulation explained 11% and 12% of the variation of mental index, and 12% and 9% of motor development, respectively. All together, they explained 23% and 21% of the variation of these indexes. Low birth weight influenced only 3% of the variation of mental index and 5% of motor index

Uso de suplementos vitamínicos e/ou minerais por crianças menores de seis meses no interior do estado de Pernambuco Use of vitamin and/or mineral supplies by infants under six months of age in the interior of Pernambuco State

OBJETIVOS: descrever o uso de suplementos vitamínicos e/ou minerais em crianças, do nascimento até o sexto mês de vida, bem como avaliar a associação entre o uso dos suplementos e características socioeconômicas, biológicas, padrões alimentares e de assistência à saúde. MÉTODOS: o estudo compreendeu uma sub-amostra de 399 crianças que pertenciam a um estudo coorte, realizado no interior de Pernambuco. RESULTADOS: a proporção de crianças que recebeu vitaminas e/ou minerais foi de 18,8%. O uso desses suplementos aumentava com a idade da criança, OR=4,38 com 17 semanas e OR=9,82 com 26 semanas de vida, quando comparadas com as crianças na idade de quatro semanas. O maior uso de suplementos foi observado naquelas crianças de melhor renda e entre aquelas que não compartilhavam o domicílio com outras menores de cinco anos. As mães com idade igual ou superior a 25 anos recorreram mais à suplementação para seus filhos do que aquelas mais jovens. A duração mediana do aleitamento materno esteve associada à suplementação de vitaminas e/ou minerais, sendo menor entre as crianças que utilizaram esses medicamentos. CONCLUSÕES: verificou-se a utilização do recurso medicamentoso como via de ingestão de vitaminas e/ou minerais em lactentes cujas necessidades nutricionais poderiam ser atendidas através do aleitamento materno exclusivo.<br>OBJECTIVES: to describe the use of vitamin and or minerals supplements in children from birth to six months of age, as well as to assess the association between supplements use and social, economic, biological features, nutrition standards and healthcare. METHODS: the study comprised a sub-sample of 399 children in a cohort study performed in the interior of Pernambuco. RESULTS: the proportion of children receiving vitamin and/or minerals supplements was of 18.8%. The use of these supplements increased with the child's age, OR=4.38 with 17 weeks and OR=9.82 with 26 weeks of age when compared with four weeks old infants. The increased use of supplements was determined in children of low income families and among the ones not sharing the home with other children under five years old. Twenty five year old or older mothers used more supplements than younger mothers. The average time for breastfeeding was associated to vitamins and/or minerals supplements use, being shorter among children using these supplements. CONCLUSIONS: the use of supplements as a means for vitamins and/or minerals offer in babies whose nutritional needs could be met through exclusive breastfeeding, was determined

Consumo alimentar de crianças em municípios de baixo índice de desenvolvimento humano no Nordeste do Brasil Food consumption of children from cities with a low human development index in the Brazilian Northeast

OBJETIVO: Este trabalho tem como objetivo analisar o consumo alimentar de crianças em Gameleira, na Zona da Mata Meridional de Pernambuco, e em São João do Tigre, no Semi-Árido da Paraíba, municípios do Nordeste do Brasil. MÉTODOS: Trata-se de estudo transversal envolvendo crianças menores de dois anos, das quais 238 em Gameleira, e 207 em São João do Tigre. O consumo alimentar foi registrado utilizando o método recordatório de 24 horas. Os nutrientes foram analisados utilizando as Dietary Referency Intakes. RESULTADOS: O consumo médio de energia e da maioria dos nutrientes esteve acima das ingestões de referência, em todas as faixas etárias e em ambos os municípios. A maioria dos valores de prevalência de risco de inadequação dos nutrientes foram elevados, principalmente de ferro e zinco, nas crianças entre 7 e 11 meses. O município de São João do Tigre apresentou prevalência de risco, com inadequação em todas as faixas etárias e nutrientes analisados, com exceção da proteína e do ferro na faixa etária entre 12 e 23 meses, embora sem diferença estatisticamente significante. CONCLUSÃO: A situação nutricional da população estudada ainda preocupa devido às acentuadas prevalências de risco de inadequação dos nutrientes. Portanto, é necessária a elaboração de estratégias que reforcem e promovam a segurança alimentar e nutricional para essas populações, a fim de evitar o risco de instalação de distúrbios nutricionais.<br>OBJECTIVE: This study analyzes the food consumption of children from Gameleira, located in the Southern Forest Area of Pernambuco, and from São João do Tigre, located in the semiarid region of Paraíba, in the Brazilian Northeast. METHODS: This cross-sectional study included 238 children from Gameleira and 207 from São João do Tigre aged <2 years. Food consumption was investigated using a 24-hour dietary recall. Nutrient intake adequacy was classified according to the Dietary Reference Intakes. RESULTS: Mean intakes of energy and most nutrients were above the reference values for all ages in both cities. The prevalences of risk of inadequate nutrient intake were high for most nutrients, especially iron and zinc, in children aged 7 to 11 months. São João do Tigre presented higher said prevalences for most studied age groups and nutrients, except for protein and iron in children aged 12 to 23 months, although the difference was not statistically significant. CONCLUSION: The nutrition situation of this population is still of concern because of the high prevalence of risk of inadequate nutrient intake. Therefore, strategies that promote and ensure food and nutrition security are needed for these populations to prevent risk of nutrition disorders