Article Archive: South American

Am J Hum Biol 22(3):336-47
1 May 2010

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.

1 July 2007

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.

Soc Sci Med 63(2):359-72
1 July 2006

Researchers have found a positive association between income inequality and poor individual health. To explain the link, researchers have hypothesized that income inequality erodes community social capital, which unleashes negative emotions, stress, and stress behaviors that hurt health. Few studies have tested the hypothesized path. Here we estimate the association between (a) village income inequality and social capital, and (b) three distinct negative emotions (anger, fear, sadness) and one stress behavior (alcohol consumption). We use four quarters of panel data (2002-2003) from 655 adults in 13 villages of a foraging-farming society in the Bolivian Amazon (Tsimane'). We found that: (1) village income inequality was associated with more negative emotions but with less alcohol consumption, (2) social capital always bore a negative association with outcomes, and (3) results held up after introducing many changes to the main model. We conclude that village income inequality probably affects negative emotions and stress behaviors through other paths besides social capital because we conditioned for social capital. One such path is an innate dislike of inequality, which might have pre-human origins. Our prior research with the Tsimane' suggests that village income inequality bore an insignificant association with individual health. Therefore, village income inequality probably affects negative emotions and stress behaviors before undermining health.

Journal of ethnobiology and ethnomedicine 2:21
1 January 2006

BACKGROUND: New quantitative methods to collect and analyze data have produced novel findings in ethnobiology. A common application of quantitative methods in ethnobiology is to assess the traditional ecological knowledge of individuals. Few studies have addressed reliability of indices of traditional ecological knowledge constructed with different quantitative methods.

METHODS: We assessed the associations among eight indices of traditional ecological knowledge from data collected from 650 native Amazonians. We computed Spearman correlations, Chronbach's alpha, and principal components factor analysis for the eight indices.

RESULTS: We found that indices derived from different raw data were weakly correlated (rho<0.5), whereas indices derived from the same raw data were highly correlated (rho>0.5; p < 0.001). We also found a relatively high internal consistency across data from the eight indices (Chronbach's alpha = 0.78). Last, results from a principal components factor analysis of the eight indices suggest that the eight indices were positively related, although the association was low when considering only the first factor.

CONCLUSION: A possible explanation for the relatively low correlation between indices derived from different raw data, but relatively high internal consistency of the eight indices is that the methods capture different aspects of an individual's traditional ecological knowledge. To develop a reliable measure of traditional ecological knowledge, researchers should collect raw data using a variety of methods and then generate an aggregated measure that contains data from the various components of traditional ecological knowledge. Failure to do this will hinder cross-cultural comparisons.

Economics and human biology 3(1):139-62
1 March 2005

We analyze anthropometric variables of a society of forager-horticulturalists in the Bolivian Amazon (Tsimane') in 2001-2002. Community variables (e.g., inequality, social capital) explain little of the variance in anthropometric indices of nutritional status, but individual-level variables (schooling, wealth) are positively correlated with nutritional status. Dietary quality (foods high in animal proteins), access to foraging technology, and traditional knowledge of medicinal plants are related to better anthropometric indices.

Soc Sci Med 61(5):907-19
1 September 2005

Evidence has been accumulated about the adverse effects of income inequality on individual health in industrial nations, but we know less about its effect in small-scale, pre-industrial rural societies. Income inequality should have modest effects on individual health. First, norms of sharing and reciprocity should reduce the adverse effects of income inequality on individual health. Second, with sharing and reciprocity, personal income will spill over to the rest of the community, attenuating the protective role of individual income on individual health found in industrial nations. We test these ideas with data from Tsimane' Amerindians, a foraging and farming society in the Bolivian Amazon. Subjects included 479 household heads (13+ years of age) from 58 villages. Dependent variables included anthropometric indices of short-run nutritional status (body-mass index (BMI), and age- and sex-standardized z-scores of mid-arm muscle area and skinfolds). Proxies for income included area deforested per person the previous year and earnings per person in the last 2 weeks. Village income inequality was measured with the Gini coefficient. Income inequality did not correlate with anthropometric indices, most likely because of negative indirect effects from the omission of social-capital variables, which would lower the estimated impact of income inequality on health. The link between BMI and income and between skinfolds and income resembled a U and an inverted U; income did not correlate with mid-arm muscle area. The use of an experimental research design might allow for better estimates of how income inequality affects social capital and individual health.

Am J Hum Biol 21(5):651-6
1 September 2009

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.

Ann Hum Biol 35(3):276-93.
1 May 2008

BACKGROUND: Global climate change and recent studies on early-life origins of well-being suggest that climate events early in life might affect health later in life.

AIM: The study tested hypotheses about the association between the level and variability of rain and temperature early in life on the height of children and adolescents in a foraging-farming society of native Amazonians in Bolivia (Tsimane'). SUBJECT AND METhods: Measurements were taken for 525 children aged 2-12 and 218 adolescents aged 13-23 in 13 villages in 2005. Log of standing height was regressed on mean annual level and mean intra-annual monthly coefficient of variation (CV) of rain and mean annual level of temperature during gestation, birth year, and ages 2-4. Controls include age, quinquennium and season of birth, parent's attributes, and dummy variables for surveyors and villages.

RESULTS: Climate variables were only related with the height of boys age 2-12. The level and CV of rain during birth year and the CV of rain and level of temperature during ages 2-4 were associated with taller stature. There were no secular changes in temperature (1973-2005) or rain (1943-2005).

CONCLUSION: The height of young females and males is well protected from climate events, but protection works less well for boys ages 2-12.

Econ Hum Biol 8(1):88-99
1 March 2010

Among adults of industrial nations, growth stunting (<-2 SD height Z score) is associated with worse indicators of adult well-being (e.g., income). Does adult stunting also inflict private costs in traditional societies? Adult stunting penalties or height premiums might only emerge when traditional societies modernize. Here we estimate the association between adult stunting and indicators of adult well-being using data from a panel study in progress among the Tsimane', a foraging-farming society of native Amazonians in Bolivia. Subjects included 248 women and 255 men >or=age 22 measured annually during 5 consecutive years (2002-2006). Nine outcomes (wealth, monetary income, illness, access to credit, mirth, schooling, math skills, plant knowledge, forest clearance) were regressed separately against a stunting dummy variable and a wide range of control variables. We found no significant association between any of the indicators of own well-being and adult stunting. Additional analysis showed that stunting bore an association only with poorer mid-arm muscle area. Height premiums and stunting penalties, though evident and marked in modern societies, might not be common in all traditional societies.