Developmental impacts of heavy metals and undernutrition

A recent Lancet series highlighted enormous loss to young children's developmental potential in developing countries, from exposure to sociocultural and health risks. The possibility that nutritional deficiencies might exacerbate the adverse impact of environmental exposures to developmental toxicants such as heavy metals and pesticides has not been explored. While both arsenic and manganese exposures have known neurotoxicity in adults, systematic investigation in young children has only recently begun. Five hundred and ninety 6- and 10-year-old Bangladeshi children participated in three overlapping studies. Well-water arsenic and manganese were measured from home wells; urine and blood samples were provided; and sociodemographic and household characteristics obtained. For new analyses, 'stunting' was defined as 2 or more standard deviations below the Centers for Disease Control and Prevention gender-specific height-for-age norms. Developmental assessments employed culturally adapted variants of the WISC-III (age 10) or WPPSI-III (age 6). In prior analyses, after adjusting for social factors, well-water arsenic and manganese were both significantly associated with poorer developmental scores at age 10; associations for water arsenic at 6 years were significant, but attenuated. Negative associations with metal exposures held up in newer analyses, and stunting was significantly associated with lower intellectual functioning in analyses considering either metal. There were no significant stunting-by-metal interactions. Developmental risks often co-occur. Millions in South Asia are exposed to naturally occurring arsenic and manganese through household wells. Stunting affects more than 25% of young children in developing countries. The combined neurocognitive loss from both risks, although rarely jointly studied, represents a substantial loss of global potential.