Blood lead levels ≤ 10 micrograms/deciliter and executive functioning across childhood development: A systematic review

At low levels, the effects of lead on specific neurocognitive processes, such as executive functioning, is not well understood. The aim of this systematic review is to synthesize the empirical literature examining the relationship between prenatal and postnatal low blood lead levels and executive function across childhood development. This review considers the unity and diversity model of executive functioning by assessing the domains of working memory, cognitive flexibility, inhibition, attention, and unitary executive function separately. Nineteen studies met the inclusion criteria and were synthesized in the review. The results suggest an inverse association between postnatal lead exposure and executive function processes across childhood. The inverse relationship between postnatal lead exposure and working memory and cognitive flexibility in middle childhood is most strongly represented. Additionally, a marginal inverse relationship between postnatal lead exposure and unitary executive functioning and attention in middle childhood is suggested. The evidence does not support a relationship between postnatal lead and inhibition in middle childhood. Although there is support for the inverse relationship between low level lead exposure and executive function, lack of repeated exposure and outcome measures limit firm conclusions. Furthermore, the long-term impact of lead exposure on executive function outcomes is relatively unknown given lack of studies on adolescent populations.