Tradeoffs between immune function and childhood growth among Amazonian forager-horticulturalists.
Level 3 - non-randomized controlled study
Prospective mixed-longitudinal cohort study with repeated measures.
PubMed 29632170 · doi:10.1073/pnas.1717522115
What was done
Researchers conducted a prospective mixed-longitudinal study in 261 Amazonian forager-horticulturalist Shuar children (aged 4–11 years) in a high-pathogen, low-resource environment. They collected baseline anthropometry (stature, subcutaneous body fat) and blood immune biomarkers (humoral and cell-mediated immune activity, acute inflammation). In subsamples, linear growth was assessed longitudinally across three distinct time intervals (1 week, 3 months, and 20 months) alongside measures of acute inflammation, and analyzed using multilevel models.
What was found
Elevated immune function showed consistent negative associations with physical growth. During periods of mildly elevated immune activity, children experienced up to a 49% reduction in linear growth. The growth-inhibiting effects were biomarker-specific over timeframes reflecting active energetic competition and were pronounced during costly acute inflammation. Children with higher baseline levels of subcutaneous body fat completely avoided the growth-inhibiting effects of acute inflammation.
Why it matters
This study provides direct field evidence in human children that immune activation trades off against linear growth under resource-limited conditions, demonstrating that body fat serves as a critical energetic buffer against infection-induced growth faltering.
Limits
The study was conducted exclusively in a single indigenous Amazonian population living in high-pathogen conditions, limiting generalizability to well-nourished, industrialized settings. The abstract does not report sample sizes for the specific longitudinal subsamples, exact biomarker cutoffs, confidence intervals, or specific statistical effect sizes beyond the percentage growth reduction.
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