An inevitable exposure to the toxic heavy metal such as lead in our environmental can have irreversible effects on children’s mental performance.In this study, 3316 children in 8 case-control studies were selected for review. The case group was exposed to a concentration of lead above 10 μg/dL, and the control group was exposed to a concentration of less than 10 μg/dL, but the duration of exposure was different among studies, and the subgroup analysis was performed based on this variable.In the subgroup with duration of exposure less than the average of 4.5 years, the difference of IQ test score between two groups was significant (MD = −3.53) (P-value <0.05). Also, in the subgroup with more than 4.5 years of duration, the difference of IQ test score was significant (MD = −22.63) (P-value < 0.001).This study demonstrates that the concentration and duration of lead exposure have a large effect on mental function in children.

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