Lead Exposure, Stunting and Language Development in Mexico: a first national study

Abstract

BACKGROUND AND AIM: Lead exposure affects language development. Poor nutrition increases lead absorption and its toxic effects. According to the 2018 National Health and Nutrition Survey (ENSANUT), there are more than 1.4 million children under 5 years of age (21.8%) with elevated blood lead levels (BLL) ( 5 µg/dL), and 14.9% presented nutritional deficiencies. Our aims were: 1) to analyze the association between lead exposure and language development in a representative sample of children aged 12–59-months and 2) to assess the potential modifying effect of this association by chronic undernutrition (stunting). METHODS: We analyzed data from the 2018 ENSANUT, a representative survey of localities with 100,000 inhabitants in Mexico. An Early Childhood Development (ECD) module with language assessment was applied to 1413 children aged 12-59 months. One child per household was randomly selected for a capillary BLL (Lead Care II, detection limit = 3.3 µg/dL) and anthropometric measurements. A multiple linear regression (MLR) model estimated the association between BLLs (categorized as below detection limit, 3.3 – 5.0 µg/dL, and above 5.0 µg/dL) and language score (continuous z-score). Furthermore, we stratified by stunting condition and all analyses were estimated according to the survey sampling design. RESULTS:26% of children had BLL 3.3 - 5.0 µg/dL and 16% above 5.0 µg/dL; 18% had stunting and mean language z-score was -0.10±1.00. Compared to children with BLL below the detection limit, children with BLLs 3.3 µg/dL showed -non statistically significant- lower language Z-score (β= -0.16, p 0.163). Children with stunting and BLL between 3.3 – 5 µg/dL had a significant reduction in language Z-score (β= -0.63, p 0.001). CONCLUSIONS:The co-exposure of lead and stunting was associated with a decrease in language score. These results add to previous research on a call for action to reduce lead exposure, particularly in children with chronic undernutrition. KEYWORDS: Lead exposure, language development, stunting