Hookworm Infection and Childhood Growth: A Critical Narrative Review of Body Mass Index, Height Standard Deviation Scores, Growth Velocity and the Insulin-like Growth Factor 1 Axis in Normal-weight and Underweight Children

Abstract

Hookworm infection remains one of the most common chronic parasitic conditions of childhood in low-resource settings, and growth impairment is routinely listed among its consequences. The evidence supporting that claim is weaker and more heterogeneous than programmatic language implies. This critical narrative review evaluates what is established, contested and unknown about the relationship between hookworm infection and four related growth constructs in children: body mass index (BMI), the BMI standard deviation score (BMI-SDS), the height standard deviation score (height-SDS) and height growth velocity, together with the insulin-like growth factor 1 (IGF-1) system that plausibly links infection to linear growth. Particular attention is given to whether these relationships differ between children who are of normal weight and those who are underweight, a stratification that carries direct implications for targeted rather than universal preventive chemotherapy. Literature was identified through structured searching of scholarly databases and indexes, supplemented by backward and forward citation searching and by examination of institutional sources, and appraised for design adequacy, exposure measurement, confounding control and analytical transparency. Three findings dominate the synthesis. First, the anthropometric evidence is overwhelmingly cross-sectional, aggregates hookworm with other soil-transmitted helminths, and rarely reports species-specific or intensity-stratified estimates, so that the apparent inconsistency between studies is substantially attributable to exposure misclassification and heterogeneous outcome definitions rather than to genuine biological divergence. Second, ponderal and linear outcomes behave differently: anthelmintic treatment trials more often show weight or BMI responses than height responses, which is consistent with the short observation windows typical of such trials but does not exclude a slower linear effect. Third, direct paediatric evidence connecting hookworm infection to the IGF-1 system is almost absent; the most informative controlled data derive from adults, and the strongest paediatric mechanistic analogue concerns Trichuris trichiura rather than hookworm. Effect modification by baseline nutritional status is biologically plausible and programmatically important, yet no adequately powered study has tested it directly with prespecified strata. Priorities include species-specific longitudinal cohorts with quantitative molecular diagnostics, IGF-1 measurement interpreted against age- and sex-specific references and adjusted for inflammation, and treatment trials with prespecified nutritional-status strata and observation periods long enough to detect linear growth responses.