Is the number of siblings associated with dietary patterns in adolescents? The 1993 birth cohort of Pelotas (Brazil).

Our study aimed to estimate the association between number of siblings and dietary patterns in adolescents. Prospective longitudinal study was developed using data from the birth cohort of the city of Pelotas, Brazil, which included 5249 participants. At the 18-year-old follow-up, from 4563 individuals located, 4106 were interviewed (follow-up rate 81.3%). Of these, 3751 were included in our principal component analysis of dietary patterns. Regular dietary intake of 45 food groups over the previous year was measured with a food frequency questionnaire. We identified four patterns, which accounted for 40% of the total variance in food group consumption. These were labeled "Protein and fast food", "Fruit and vegetables", "Common Brazilian", and "Sweets, soft drinks, and dairy products". Crude and adjusted analyses of the association between number of siblings and dietary patterns were performed using linear regression. The number of siblings was positively associated with a higher adherence to each dietary pattern, with the exception of the "Common Brazilian" patterns, for which there was no apparent relationship with number of siblings. The findings showed that a greater number of siblings is related to a more diverse diet in the later adolescence, which may predict better nutrient adequacy and health outcomes.

The influence of birth order and number of siblings on adolescent body composition: evidence from a Brazilian birth cohort study.

The aim of this study was to estimate the association between birth order and number of siblings with body composition in adolescents. Data are from a birth cohort study conducted in Pelotas, Brazil. At the age of 18 years, 4563 adolescents were located, of whom 4106 were interviewed (follow-up rate 81.3 %). Of these, 3974 had complete data and were thus included in our analysis. The variables used in the analysis were measured during the perinatal period, or at 11, 15 and/or 18 years of age. Body composition at 18 years was collected by air displacement plethysmography (BOD POD®). Crude and adjusted analyses of the association between birth order and number of siblings with body composition were performed using linear regression. All analyses were stratified by the adolescent sex. The means of BMI, fat mass index and fat-free mass index among adolescents were 23.4 (sd 4.5) kg/m², 6.1 (sd 3.9) kg/m² and 17.3 (sd 2.5) kg/m², respectively. In adjusted models, the total siblings remained inversely associated with fat mass index (ß = - 0.37 z-scores, 95 % CI - 0.52, - 0.23) and BMI in boys (ß = - 0.39 z-scores, 95 % CI - 0.55, - 0.22). Fat-free mass index was related to the total siblings in girls (ß = 0.06 z-scores, 95 % CI - 0.04, 0.17). This research has found that number of total siblings, and not birth order, is related to the fat mass index, fat-free mass index and BMI in adolescents. It suggests the need for early prevention of obesity or fat mass accumulation in only children.

Challenges in modelling the random structure correctly in growth mixture models and the impact this has on model mixtures.

Lifecourse trajectories of clinical or anthropological attributes are useful for identifying how our early-life experiences influence later-life morbidity and mortality. Researchers often use growth mixture models (GMMs) to estimate such phenomena. It is common to place constrains on the random part of the GMM to improve parsimony or to aid convergence, but this can lead to an autoregressive structure that distorts the nature of the mixtures and subsequent model interpretation. This is especially true if changes in the outcome within individuals are gradual compared with the magnitude of differences between individuals. This is not widely appreciated, nor is its impact well understood. Using repeat measures of body mass index (BMI) for 1528 US adolescents, we estimated GMMs that required variance-covariance constraints to attain convergence. We contrasted constrained models with and without an autocorrelation structure to assess the impact this had on the ideal number of latent classes, their size and composition. We also contrasted model options using simulations. When the GMM variance-covariance structure was constrained, a within-class autocorrelation structure emerged. When not modelled explicitly, this led to poorer model fit and models that differed substantially in the ideal number of latent classes, as well as class size and composition. Failure to carefully consider the random structure of data within a GMM framework may lead to erroneous model inferences, especially for outcomes with greater within-person than between-person homogeneity, such as BMI. It is crucial to reflect on the underlying data generation processes when building such models.

The spatial distribution of overweight and obesity among a birth cohort of young adult Filipinos (Cebu Philippines, 2005): an application of the Kulldorff spatial scan statistic.

OBJECTIVES: The objectives of the study were to test for spatial clustering of obesity in a cohort of young adults in the Philippines, to estimate the locations of any clusters, and to relate these to neighborhood-level urbanicity and individual-level socioeconomic status (SES). SUBJECTS: Data are from a birth cohort of young adult (mean age 22 years) Filipino males (n=988) and females (n=820) enrolled in the Cebu Longitudinal Health and Nutrition Survey. METHODS: We used the Kulldorff spatial scan statistic to detect clusters associated with unusually low or high prevalences of overweight or obesity (defined using body mass index, waist circumference and body fat percentage). Cluster locations were compared to neighborhood-level urbanicity, which was measured with a previously validated scale. Individual-level SES was adjusted for using a principal components analysis of household assets. RESULTS: High-prevalence clusters were typically centered in urban areas, but often extended into peri-urban and even rural areas. There were also differences in clustering by both sex and the measure of obesity used. Evidence of clustering in males, but not females, was much weaker after adjustment for SES.

Identifying infants at risk of becoming obese: can we and should we?

OBJECTIVES: Increased understanding of the risk factors for childhood obesity has raised the possibility of identifying infants who are at risk of becoming overweight or obese, enabling early intervention for infants at high risk. This paper considers the known risk factors, describes statistical work aimed at identifying risk, and considers the ethical and practical issues of such a development. STUDY DESIGN AND METHODS: An overview of the published evidence for risk factors in the early development of overweight and obesity, and a statistical assessment of the practicality of developing a simple obesity risk assessment tool (ORT) for use in the primary care setting. RESULTS: Analysis of data from two currently available UK birth cohort studies suggests that an ORT based on these data does not provide acceptable levels of specificity and sensitivity for use in a primary care setting. CONCLUSION: Further development of an ORT using additional data and enhanced statistical analysis may lead to a practical tool. However the practical, ethical and legal issues involved in its use, and the public health policy considerations that follow must be resolved.

Does lower birth order amplify the association between high socioeconomic status and central adiposity in young adult Filipino males?

OBJECTIVES: To test the hypothesis that lower birth order amplifies the positive association between socioeconomic status and central adiposity in young adult males from a lower income, developing country context. DESIGN: The Cebu Longitudinal Health and Nutrition Survey is an ongoing community-based, observational study of a 1-year birth cohort (1983). SUBJECTS: 970 young adult males, mean age 21.5 years (2005). MEASUREMENTS: Central adiposity measured by waist circumference; birth order; perinatal maternal characteristics including height, arm fat area, age and smoking behavior; socioeconomic status at birth and in young adulthood. RESULTS: Lower birth order was associated with higher waist circumference and increased odds of high waist circumference, even after adjustment for socioeconomic status in young adulthood and maternal characteristics that could impact later offspring adiposity. Furthermore, the positive association between socioeconomic status and central adiposity was amplified in individuals characterized by lower birth order. CONCLUSIONS: This research has failed to reject the mismatch hypothesis, which posits that maternal constraint of fetal growth acts to program developing physiology in a manner that increases susceptibility to the obesogenic effects of modern environments.

A structural equation model of the developmental origins of blood pressure.

BACKGROUND: Birth-size is a problematic proxy for the fetal environment, and regression models testing for associations between birth-size and blood pressure have been criticized. METHODS: We modelled fetal environment as a latent variable determined by maternal height and arm fat area (AFA) during pregnancy using structural equation modelling. We tested for associations between latent fetal environment (LFE) and systolic blood pressure (SBP) while controlling for birth weight (BW) and current weight (CW). Data are from 1435 male and 1218 female young adult Filipinos (2005; mean age 21 years) enrolled in the Cebu Longitudinal Heath and Nutrition Survey, an ongoing, community-based study of a one-year birth cohort. Using AMOS 6.0, LFE was modelled as a determinant of BW, CW and SBP; CW was modelled as a determinant of SBP. RESULTS: Overall model fit was excellent (chi2: 32.14, 27 df, P=0.23). The estimated direct relationship between LFE and SBP was inverse for both males ((-0.43) -0.26 (-0.10)) and females ((-0.29) -0.18 (-0.07)). CONCLUSIONS: These results are consistent with the hypothesis that maternal height and AFA impact fetal development in a manner that is positively associated with fetal growth (as reflected by BW) and inversely associated with SBP in young adulthood.