Differences in Tsimane children’s growth outcomes and associated determinants as estimated by WHO standards vs. within-population references

Abstract

Anthropometric measures are commonly converted to age stratified z-scores to examine variation in growth outcomes in mixed-age and sex samples. For many study populations, z-scores will differ if calculated from World Health Organization (WHO) growth standards or within-population references. The specific growth reference used may influence statistical estimates of growth outcomes and their determinants, with implications for biological inference. We examined factors associated with growth outcomes in a sample of 152 Tsimane children aged 0–36 months. The Tsimane are a subsistence-scale population in the Bolivian Amazon with high rates of infectious disease and growth faltering. To examine the influence of growth reference on statistical inferences, we constructed multiple plausible models from available infant, maternal, and household attributes. We then ran identical models for height-for-age (HAZ), weight-for-age (WAZ), and weight-for-height (WHZ), with z-scores alternately calculated from WHO and robust Tsimane Lambda-Mu-Sigma growth curves. The distribution of WHO relative to Tsimane HAZ scores was negatively skewed, reflecting age-related increases in lower HAZ. Standardized coefficients and significance levels generally agreed across WHO and Tsimane models, although the strength and significance of specific terms varied in some models. Age was strongly, negatively associated with HAZ and WAZ in nearly all WHO, but not Tsimane models, resulting in consistently higher R 2 estimates. Age and weaning effects were confounded in WHO models. Biased estimates of determinants associated with WHO HAZ may be more extreme in small samples and for variables that are strongly age-patterned. Additional methodological considerations may be warranted when applying WHO standards to within-population studies, particularly for populations with growth patterns known to systematically deviate from those of the WHO reference sample.

Epigenetic aging in children from a small‐scale farming society in The Congo Basin: Associations with child growth and family conflict

“…To avoid further restricting the sample sizes in our analyses, we focused on the WFH and height‐for‐age measures. We transformed the age‐ and sex‐adjusted values for WFH and height‐for‐age to z‐scores prior to our analyses, producing local standards for growth based on the data available in our study, which can provide insights into local variation in health in settings such as this (Martin, Blackwell, Kaplan, & Gurven, ).…”

Effects of a mixed‐subsistence diet on the growth of Hadza children

“…However, given the rapid pace of change, this is a trend that warrants continuous monitoring (Wells et al, 2020). Future research should include a larger sample size and measure other factors that have been shown to regulate growth, including pathogenic load (Urlacher et al, 2018), weaning practices (Martin et al, 2019), and social-economic stressors (Bogin, Scheffler, & Hermanussen, 2017). Additionally, a Hadza specific growth reference would strengthen future analyses.…”

“…The normal curves for the WHO standardized population should not be considered “normal” for small‐scale foragers, as the WHO curves do not capture all population variation and may overestimate stunting/wasting in small‐scale societies (see Martin, Blackwell, Kaplan, & Gurven, 2019; Perumal, Bassani, & Roth, 2018). Ideally, a population specific reference would be utilized for this study; however, because no Hadza reference exists, we compared our sample against the widely accepted WHO standard.…”

Understanding Growth and Malnutrition in Baka Pygmy Children

“…These groups exhibit large variations in stature but have characteristically small body size (Stinson 1990(Stinson , 2012Natale and Rajagopalan 2014;Urlacher et al 2016;Olivero et al 2016;Blackwell et al 2017). A study of children of the Shuar of Ecuador and the Tsiname of Bolivia (Urlacher et al 2016;Blackwell et al 2017;Martin et al 2019) found that using WHO standards stunting rates were 40%, corresponding to about the median stunting rates in indigenous Amazonians (Foster et al 2005). For Amazonians in general, high rates of child stunting but low rates of underweight (low weight for age) and wasting are typical, suggesting the effect of shared environmental challenges such as high heat, humidity, and pathogen density, and low food availability (Blackwell et al 2017;Perry and Verdu 2017).…”

“…However, despite the fact that genetic adaptation to tropical forest habitats has been extensively considered (Schell and Magnus 2007;Urlacher et al 2016), nutritional insufficiency and infectious disease are generally suggested as being the main causes of small stature (Stinson 1990(Stinson , 2012Orr et al 2001;Foster et al 2005). In the Tsimane study (Martin et al 2019), the authors suggest that WHO growth standards "remain ideal for between-population comparisons and assessment of largescale health interventions" but should be used in combination with a population-specific growth reference (Blackwell et al 2017).…”