Sibling composition and children's anthropometric indicators of nutritional status: Evidence from native Amazonians in Bolivia

Background: Siblings compete for parental resources. Little is known about how sibling composition (older sisters, older brothers, younger sisters, younger brothers) might affect child anthropometric indicators of nutritional status. Aim: This study evaluates the associations between sibling composition and child anthropometry using panel data from a native Amazonian society (Tsimane'). Methods: Anthropometry of similar to 168 girls and 169 boys aged 2-9 years were measured annually during 2002-2007 (2360 observations). Children's weight-for-height Z-score (WHZ), mid-upper arm circumference (MUAC), mid-upper arm muscle area (AMA) and triceps skin-fold thickness (TST) were regressed separately against all of the sibling composition variables while controlling for child's age and survey year. Multivariate panel linear regressions were used with individual, village, survey year and village-year fixed-effects, clustering by household. Results: Among girls, an additional older brother was associated with a 1.4% decrease in MUAC (p < 0.01) and a 4.3% decrease in AMA (p < 0.01); an additional younger sister was associated with a 6.3% decrease in TST (p < 0.01). The association between sibling composition and arm anthropometry was robust to various model specifications. Conclusion: Older brothers and younger sisters were negatively associated with arm measures in girls. This finding may help improve policy interventions that aim to address children's nutritional health and long-term wellbeing.