Hair, serum and urine chromium levels in children with cognitive defects: A systematic review and meta-analysis of case control studies.

Environmental chromium exposure may cause impaired development of children. We conducted a systematic review and meta-analysis. Electronic databases including PubMed, Embase, Web of Science and CINAHL were searched to identify case-control studies that reported childhood Cr exposure and cognitive development. The Newcastle-Ottawa Scale (NOS) was used to ensure the quality of the included studies. Cr levels were compared in cases and controls, and a random effect meta-analysis was performed using Stata version 16. Twelve of 61 studies identified in the literature search were eligible for this analysis. Hair, serum and urine Cr measurements were reported by seven, two and one studies, respectively. In addition, one study reported both serum and hair Cr exposure and another reported urine and hair Cr exposure. The pooled standard mean differences (SMD) showed that hair Cr levels were non-significantly lower among children with cognitive defects (-0.01 μg/g, 95% CI: -0.04, 00, p = 0.27). In serum and urine, the pooled SMD was higher in children with cognitive deficits compared with healthy control children (0.32 μg/g, 95% CI: -0.78, 1.42, p = 0.56 and 0.64 μg/g, CI: -0.07,1.36, p = 0.08; respectively). In summary, this systematic review found no significant differences in hair, serum and urine Cr levels between children with cognitive deficits and healthy control children when all study data were pooled in the meta-analysis. Larger studies using standardized criteria and longitudinal assessment of cognitive development are needed to determine whether there is a dose response effect of childhood Cr exposure on cognitive development of children.