The ubiquity and consequences of childhood growth stunting (<-2 SD in height-for-age Z score, HAZ) in rural areas of low-income nations has galvanized research into the reversibility of stunting, but the shortage of panel data has hindered progress. Using panel data from a native Amazonian society of foragers-farmers in Bolivia (Tsimane'), we estimate rates of catch-up growth for stunted children. One hundred forty-six girls and 158 boys 2 < or = age < or = 7 were measured annually during 2002-2006. Annual Delta height in cm and in HAZ were regressed separately against baseline stunting and control variables related to attributes of the child, mother, household, and village. Children stunted at baseline had catch-up growth rates 0.11 SD/year higher than their nonstunted age and sex peers, with a higher rate among children farther from towns. The rate of catch up did not differ by the child's sex. A 10% rise in household income and an additional younger sibling lowered by 0.16 SD/year and 0.53 SD/year the rate of growth. Results were weaker when measuring Delta height in cm rather than in HAZ. Possible reasons for catch-up growth include (a) omitted variable bias, (b) parental reallocation of resources to redress growth faltering, particularly if parents perceive the benefits of redressing growth faltering for child school achievement, and (c) developmental plasticity during this period when growth rates are most rapid and linear growth trajectories have not yet canalized.
Article Archive: Bolivia/epidemiology
Researchers have shown interest in the relation between (a) social capital and individual income and (b) the individual health of people of industrial nations. The socioeconomic complexity of industrial nations makes it difficult to arrive at firm conclusions. We circumvent the obstacle by using data from a small-scale rural society of foragers-farmers in the Bolivian Amazon (Tsimane'). We examine the interactions between the outcome (BMI) and relative income, relative social capital, village income, and village social capital. We test three hypotheses: people in villages with more social capital should have higher BMI, the positive association between social capital and BMI will be more marked among the less well-off, and better-off people who display generosity will have higher BMI than better-off people who do not. On the methodological side we show the importance of: focusing on relative measures of income and social capital, estimating interaction between community and relative measures of income and social capital, and showing results through contour plots that summarize the relation between BMI and pairs of explanatory variables. On the substantive side we find evidence that village social capital and village income complement each other and are associated with higher BMI, the rich who are stingy have lower BMI than the rich who display generosity, and increase in village income might reduce individual incentives to invest in social capital. We explore interactions between explanatory variables and their influence on BMI, and end by recommending the use of an experimental research design to obtain unbiased estimates of causal effects.
Leptin is thought to signal energy stores, thus helping the body balance energy intake and expenditure. However, the strong relationship between leptin and adiposity in populations with adequate nutrition or common obesity is not universal across ecologic contexts, and leptin often correlates only weakly, or not at all, with adiposity in populations of lean or marginally-nourished males. To clarify whether the relationship between adiposity and leptin changes during development, this study examines leptin and body fat among children and adolescents of lowland Bolivia. Anthropometric measures of body composition and dried blood spot samples were collected from 487 Tsimane' ranging from 2 to 15 years of age. Leptin was assayed using an enzyme immunoassay protocol validated for use with blood spot samples. In this population, leptin concentrations were among the lowest reported in a human population (mean +/- SD: 1.26 +/- 0.5 and 0.57 +/- 0.3 in females and males). In addition, the relationship between leptin and adiposity follows distinct developmental trajectories in males and females. In males, leptin is weakly correlated with most measures of body composition at all ages investigated. However, in females, the level of body fat and the strength of the correlation between body fat and leptin (a measure of its strength as a signal of energy stores) both increase markedly with age. These findings suggest a more important role of leptin as a signal of energy stores among females as they approach reproductive maturity, while raising questions about the function of this hormone in lean males.
Infectious disease, such as diarrheal disease, respiratory infections, and parasitic infections, are an important source of nutritional and energetic stress in many populations. Inspired by the research and methodological innovations of A. Roberto Frisancho, this work considers the impact of childhood environment and local disease ecology on child health and nutritional patterns among an indigenous group in lowland Bolivia. Specifically, we examine the association between soil-transmitted helminth infection, especially hookworm species, and anthropometric markers of short- and long-term nutritional status. Fecal samples, anthropometric dimensions, and health interviews were collected for 92 children ranging in age from 2.0 to 10.9 years. Microscopic examination revealed high levels of parasitic infection, with 76% of children positive for hookworm species infections (77% of girls and 74% of boys). Less common infections included Ascaris lumbricoides, Trichurius trichiura, and Strongyloides stercoralis with only 15% of children positive for multiple-species infections. After adjusting for sex and age, no statistically significant associations were observed between helminth infections and the frequency of reported illness or anthropometric measures of nutritional status. These data demonstrate the difficulty of assessing nutritional impacts of endemic infections.
Infectious disease is a major global determinant of child morbidity and mortality, and energetic investment in immune defenses (even in the absence of overt disease) is an important life-history variable, with implications for human growth and development. This study uses a biomarker of immune activation (C-reactive protein) to investigate an important aspect of child health among the Tsimane', a relatively isolated Amerindian population in lowland Bolivia. Our objectives are twofold: 1) to describe the distribution of CRP by age and gender in a cross-sectional sample of 536 2-15-year-olds; and 2) to explore multiple measures of pathogen exposure, economic resources, and acculturation as predictors of increased CRP. The median blood-spot CRP concentration was 0.73 mg/l, with 12.9% of the sample having concentrations greater than 5 mg/L, indicating a relatively high degree of immune activation in this population. Age was the strongest predictor of CRP, with the highest concentrations found among younger individuals. Increased CRP was also associated with higher pathogen exposure, lower household economic resources, and increased maternal education and literacy. The measurement of CRP offers a direct, objective indicator of immune activation, and provides insights into a potentially important pathway through which environmental quality may shape child growth and health.
Recent research documents the effects of adverse conditions during gestation and early childhood on growth responses and health throughout life. Most research linking adverse conditions in early life with adult health comes from industrial nations. We know little about the plasticity of growth responses to environmental perturbations early in life among foragers and horticulturalists. Using 2005 data from 211 women and 215 men 20+ years of age from a foraging-horticultural society of native Amazonians in Bolivia (Tsimane'), we estimate the association between (a) adult height and (b) rainfall amount and variability during three stages in the life cycle: gestation (year 0), birth year (year 1), and years 2-5. We control for confounders such as height of the same-sex parent. Rainfall amount and variability during gestation and birth year bore weak associations with adult height, probably from the protective role of placenta