Urinary concentrations of non-essential and essential elements during weaning in infants from the NELA cohort in Spain.

Infancy is a period of continuous growth and development, where inadequate intake of essential elements and exposure to non-essential elements may have lifelong health consequences. Thus, the aim of this study is to evaluate the urine concentration of essential and non-essential elements as a proxy for internal exposure during the weaning period, from 3 to 18 months of age. The Nutrition in Early Life and Asthma (NELA) birth cohort generated the data for this study. Sociodemographic, dietary, and urine concentration of essential (Co, Cu, Mo, I, Fe, Mn, Se, Zn, and Ni) and non-essential elements (Al, V, As, Cd, Sb, Tl, and Pb) data were available for 490 participants at 3 months of age and 216 participants at 18 months of age. Paired urine samples at both time periods were available for 175 infants. At 3 months of age, exclusively breastfed infants had lower urine concentrations of Al, V, Fe, Co, Se, Sb, and Tl. Notably, the concentration of Mo had a median (IQR) of 0.60 (0.40-2.10) μg/L compared to a median (IQR) of 39.80 (25.00-56.40) μg/L observed in infants exclusively fed with formula. When we analyzed the change in urine elements concentrations between 3 and 18 months of age, we observed increased As (0.75 vs. 18.60 μg/L), Co (0.05 vs. 0.24 μg/L), Mo (1.98 vs. 50.0 μg/L), Pb (0.15 vs. 0.69 μg/L), Se (11.3 vs. 23.1 μg/L), Tl (0.02 vs. 0.11 μg/L), and V (0.05 vs. 0.11 μg/L). For Cu, lower urine concentrations were observed at 18 months of age in comparison with concentrations at 3 months (5.77 vs. 4.41 μg/L). Among the main food items identified as driving the changes in urine concentration between 3 and 18 months of age were white fish, rice and pasta, potato chips, custard, small blue fish, and legumes. Exclusively breastfed infants showed lower exposure to non-essential elements compared to those who were fed with a mixture or formula. With the introduction of solid foods, the exposure to some non-essential elements increased drastically, as in the case of As and Pb. In addition, exposure to the essential metal Mo also increased substantially with the introduction of solid food.