Blood lead levels and cognitive functioning: A meta-analysis

Abstract

ObjectiveThe neurotoxicity of lead is well-known and even low exposure levels potentially impact neurocognitive abilities. This metaanalysis aimed to investigate associations between neurocognitive performance and lead exposure in adults and further assess potential effect thresholds. Material and methodsArticles indexed in Medline published until January 2017 reporting associations between lead exposure, blood lead, cognitive abilities and sensomotoric performance were included. The unbiased, standardized mean differences g between lead exposure and control groups extracted from the primary studies were pooled using a three-level, random-effects meta-analytic model with a restricted maximum likelihood estimator. Moderator analyses were conducted using weighted, mixedeffects regression analyses. ResultsWe identified 22 articles (n=3,849 participants, mean age 39.94±7.87years) published between 1976 and 2014 reporting lead exposure effects on cognitive and sensomotoric parameters (verbal abilities, visuospatial abilities, memory, attention, psychomotor function). On average, blood lead concentrations were 21.09±6.44 μg/dl higher in exposed than in control subjects. After exclusion of outliers, the random-effects three-level meta-analysis identified a significant (p<.001) pooled mean difference between exposure and control groups. Except for a smaller effect in the digit symbol test (p<.05), lead exposure did not result in different outcomes across the examined cognitive measures. Based on a marginally significant (p=.06) effect of difference in exposure levels, a blood lead increase of 10 μg/dl translated into a decline in cognitive abilities of Hedges g=.09. ConclusionsNeurocognitive performance in adults with occupational or environmental lead exposure was significant impaired with regard to the examined parameters. However, further studies are needed for the determination of effect thresholds and reversibility.