Exposure to environmental (chemical and biological) hazards and children undernutrition: A scoping review

Childhood undernutrition remains a major global public health concern, particularly in the Global South, where it contributes significantly to morbidity, mortality, and long-term developmental deficits. Increasing evidence suggests that environmental exposures-both chemical and biological-play a critical but under-recognized role in the etiology of undernutrition in children under five years of age. This scoping review synthesizes evidence from studies published between January 2014 and March 2024 on the individual and combined effects of exposure to environmental chemical and biological hazards on undernutrition outcomes in early childhood. We reviewed peer-reviewed literature examining associations between exposure to metals (e.g., lead, cadmium), air pollutants (e.g., particulate matter with a diameter of 2.5 μm or less (PM_2.5), carbon monoxide), natural toxins (e.g., aflatoxins), and infectious agents (e.g., malaria parasites, helminths) and undernutrition markers such as stunting, wasting, underweight, and anaemia in children under five. Prenatal and early-life exposure to heavy metals and air pollutants was consistently associated with impaired growth, stunting, and anaemia. Aflatoxin exposure was linked to growth suppression, while malaria and helminth infections were associated with wasting and anaemia, especially in sub-Saharan Africa and Asia. Despite the biological plausibility of synergistic or additive effects, few studies have assessed the impact of co-exposure to multiple environmental hazards on childhood undernutrition. Undernutrition in children is influenced not only by diet and infection but also by environmental exposures that disrupt nutrient utilization and growth. The limited number of studies addressing combined exposures highlights a critical research gap. Addressing childhood undernutrition requires a multisectoral approach that integrates nutrition, environmental health, WASH (water, sanitation, and hygiene), pollution control, and public health education. Nutritional interventions alone are insufficient unless environmental risk factors are simultaneously addressed.