Comparative Models of Biological and Social Pathways to Predict Child Growth through Age 2 Years from Birth Cohorts in Brazil, India, the Philippines, and South Africa.

Background: Early growth faltering accounts for one-third of child deaths, and adversely impacts the health and human capital of surviving children. Social as well as biological factors contribute to growth faltering, but their relative strength and interrelations in different contexts have not been fully described. Objective: The aim of this study was to use structural equation modelling to explore social and biological multidetermination of child height at age 2 y in longitudinal data from 4 birth cohort studies in low- and middle-income countries. Methods: We analyzed data from 13,824 participants in birth cohort studies in Brazil, India, the Philippines, and South Africa. We used exploratory structural equation models, with height-for-age at 24 mo as the outcome to derive factors, and path analysis to estimate relations among a wide set of social and biological variables common to the 4 sites. Results: The prevalence of stunting at 24 mo ranged from 14.0% in Brazil to 67.7% in the Philippines. Maternal height and birthweight were strongly predictive of height-for-age at 24 mo in all 4 sites (all P values <0.001). Three social-environmental factors, which we characterized as "child circumstances," "family socioeconomic status," and "community facilities," were identified in all sites. Each social-environmental factor was also strongly predictive of height-for-age at 24 mo (all P values <0.001), with some relations partly mediated through birthweight. The biological pathways accounted for 59% of the total explained variance and the social-environmental pathways accounted for 41%. The resulting path coefficients were broadly similar across the 4 sites. Conclusions: Early child growth faltering is determined by both biological and social factors. Maternal height, itself a marker of intergenerational deprivation, strongly influences child height at 2 y, including indirect effects through birthweight and social factors. However, concurrent social factors, many of which are modifiable, directly and indirectly contribute to child growth. This study highlights opportunities for interventions that address both biological and social determinants over the long and short term.

Birth order and number of siblings and their association with overweight and obesity: a systematic review and meta-analysis.

Context: The effect of both birth order and number of siblings on overweight and/or obesity has not been determined. Birth order and sibsize have been mathematically coupled to overweight and/or obesity, but thus far their respective effects have been estimated separately. Objective: The aim of this systematic review was to evaluate the effects of both birth order and number of siblings on the risk of overweight/obesity. Data Sources: The electronic databases MEDLINE, Social Science, SocINDEX, PsycINFO, CINAHL Plus, and Academic Search Complete were searched systematically. Study Selection: Titles and abstracts of 1698 records were examined. After 1504 records were excluded, 2 authors independently assessed the full text of all remaining papers (n = 194); disagreements were resolved by discussion. Data Extraction: A standardized form for assessment of study quality and evidence synthesis was used to extract data from the included studies. Results: Twenty studies were included in the systematic review, 14 of which were included in the meta-analysis. Meta-analyses showed that lower (vs higher) birth order and smaller (vs greater) number of siblings were associated with overweight and/or obesity, with ORs of 1.47 (95%CI, 1.12-1.93) and 1.46 (95%CI, 1.17-1.84), respectively. However, among the 9 studies that attempted to separate the effects of birth order and number of siblings in the same analysis, a higher risk of overweight/obesity was consistently found among individuals without siblings than among those with 1 or more siblings, rather than among firstborns more generally. Conclusion: The results show that both lower birth order and lower number of siblings are associated with risk of overweight/obesity, which suggests that only children are at a slightly increased risk of overweight/obesity. Systematic Review Registration: PROSPERO registration number CRD42014015135.

Correlates of self-reported weekday sleep duration in adolescents: the 18-year follow-up of the 1993 Pelotas (Brazil) Birth Cohort Study.

OBJECTIVE: To investigate factors associated with sleep duration in adolescence. METHODS: Data are from the 1993 Pelotas Birth Cohort Study of 5249 live births. Of these individuals, 4563 were located for follow-up at 18 years of age, and 4106 agreed to be interviewed (follow-up rate 81.3%). Sleep duration was continuously assessed by survey as hours per weekday. Additional covariates were collected during the perinatal period and at the 11- and 18-year follow-ups. Linear regression models were used to estimate associations between sleep duration and its hypothesized influences. All analyses were sex-stratified. RESULTS: The average sleep duration among participants was 8.4 hours (standard deviation 1.9). Longer sleep duration at 18 years of age was associated with the following perinatal factors: low maternal schooling, low family income, maternal black skin color, and low birth weight; and with the following factors measured at 18 years of age: being out of school, low achieved schooling, low family income, absence of depressive symptoms, and high screen time. CONCLUSION: Social and demographic variables may play an important role in determining adolescents' sleep duration, but the nature of these relationships in Brazil may differ from those observed in higher-income contexts.

Sleep Duration Trajectories and Body Composition in Adolescents: Prospective Birth Cohort Study.

We aimed to estimate the association between sleep duration trajectories and body composition in adolescents. We used data from participants of the 1993 Pelotas (Brazil) Birth Cohort Study who were later followed up at age 18 years (response rate of 81.3%). At the time, 3974 adolescents had complete data on body composition, which was assessed by air displacement plethysmography. Sleep duration was self-reported by participants at ages 11 and 18 years. Analyses were sex-stratified. The mean sleep duration at 11 years was 9.7 (SD 1.4) and 8.4 (SD 1.9) at 18 years. Sleep duration was dichotomized as inadequate (<8 hours/day) or adequate (≥8 hours/day). Mean body mass, fat mass, and fat-free mass indices at 18 years were 23.4 kg/m2 (SD 4.5), 6.1 kg/m2 (SD 3.9) and 17.3 kg/m2 (SD 2.5), respectively. Girls who reported inadequate sleep duration at 11 years of age, but adequate sleep duration at 18, on average experienced an increase in body mass index (ß = 0.39 z-scores; 95% CI 0.13, 0.65), fat mass index (ß = 0.30 z-scores; 95% CI 0.07, 0.53), and fat-free mass index (ß = 0.24 z-scores; 95% CI 0.08, 0.39) compared to those who had adequate sleep duration at both time points. The results suggest that changes in sleep duration across adolescence may impact body composition in later adolescence and that this may differ by sex.

Associations of linear growth and relative weight gain during early life with adult health and human capital in countries of low and middle income: findings from five birth cohort studies.

BACKGROUND: Fast weight gain and linear growth in children in low-income and middle-income countries are associated with enhanced survival and improved cognitive development, but might increase risk of obesity and related adult cardiometabolic diseases. We investigated how linear growth and relative weight gain during infancy and childhood are related to health and human capital outcomes in young adults. METHODS: We used data from five prospective birth cohort studies from Brazil, Guatemala, India, the Philippines, and South Africa. We investigated body-mass index, systolic and diastolic blood pressure, plasma glucose concentration, height, years of attained schooling, and related categorical indicators of adverse outcomes in young adults. With linear and logistic regression models, we assessed how these outcomes relate to birthweight and to statistically independent measures representing linear growth and weight gain independent of linear growth (relative weight gain) in three age periods: 0-2 years, 2 years to mid-childhood, and mid-childhood to adulthood. FINDINGS: We obtained data for 8362 participants who had at least one adult outcome of interest. A higher birthweight was consistently associated with an adult body-mass index of greater than 25 kg/m(2) (odds ratio 1·28, 95% CI 1·21-1·35) and a reduced likelihood of short adult stature (0·49, 0·44-0·54) and of not completing secondary school (0·82, 0·78-0·87). Faster linear growth was strongly associated with a reduced risk of short adult stature (age 2 years: 0·23, 0·20-0·52; mid-childhood: 0·39, 0·36-0·43) and of not completing secondary school (age 2 years: 0·74, 0·67-0·78; mid-childhood: 0·87, 0·83-0·92), but did raise the likelihood of overweight (age 2 years: 1·24, 1·17-1·31; mid-childhood: 1·12, 1·06-1·18) and elevated blood pressure (age 2 years: 1·12, 1·06-1·19; mid-childhood: 1·07, 1·01-1·13). Faster relative weight gain was associated with an increased risk of adult overweight (age 2 years: 1·51, 1·43-1·60; mid-childhood: 1·76, 1·69-1·91) and elevated blood pressure (age 2 years: 1·07, 1·01-1·13; mid-childhood: 1·22, 1·15-1·30). Linear growth and relative weight gain were not associated with dysglycaemia, but a higher birthweight was associated with decreased risk of the disorder (0·89, 0·81-0·98). INTERPRETATION: Interventions in countries of low and middle income to increase birthweight and linear growth during the first 2 years of life are likely to result in substantial gains in height and schooling and give some protection from adult chronic disease risk factors, with few adverse trade-offs. FUNDING: Wellcome Trust and Bill & Melinda Gates Foundation.

Size at birth, weight gain in infancy and childhood, and adult blood pressure in 5 low- and middle-income-country cohorts: when does weight gain matter?

BACKGROUND: Promoting catch-up growth in malnourished children has health benefits, but recent evidence suggests that accelerated child weight gain increases adult chronic disease risk. OBJECTIVE: We aimed to determine how birth weight (BW) and weight gain to midchildhood relate to blood pressure (BP) in young adults. DESIGN: We pooled data from birth cohorts in Brazil, Guatemala, India, the Philippines, and South Africa. We used conditional weight (CW), a residual of current weight regressed on prior weights, to represent deviations from expected weight gain from 0 to 12, 12 to 24, 24 to 48 mo, and 48 mo to adulthood. Adult BP and risk of prehypertension or hypertension (P/HTN) were modeled before and after adjustment for adult body mass index (BMI) and height. Interactions of CWs with small size-for-gestational age (SGA) at birth were tested. RESULTS: Higher CWs were associated with increased BP and odds of P/HTN, with coefficients proportional to the contribution of each CW to adult BMI. Adjusted for adult height and BMI, no child CW was associated with adult BP, but 1 SD of BW was related to a 0.5-mm Hg lower systolic BP and a 9% lower odds of P/HTN. BW and CW associations with systolic BP and P/HTN were not different between adults born SGA and those with normal BW, but higher CW at 48 mo was associated with higher diastolic BP in those born SGA. CONCLUSIONS: Greater weight gain at any age relates to elevated adult BP, but faster weight gains in infancy and young childhood do not pose a higher risk than do gains at other ages.