Childhood lead exposure linked to lower cognitive function, socioeconomic status in adulthood
Lead exposure in childhood appears to negatively impact cognition and socioeconomic status in adulthood, according to a New Zealand study.
“The findings expand knowledge about the persistence of the adverse effects of early-life [lead] exposure,” said Professor David Bellinger from the Harvard T.H. Chan School of Public Health in Boston, Massachusetts, US, in a separate editorial. [JAMA 2017;317:1219-1220]
After adjusting for covariates (maternal IQ, childhood IQ, and childhood socioeconomic status), adults whose childhood (age 11 years) blood lead levels exceeded 10 µg/dL had 2.73 lower mean IQ points (95 percent confidence interval [CI], -4.34 to -1.12; p<0.001) and 3.42 lower mean socioeconomic units (95 percent CI, -5.98 to -0.85; p=0.009) than those with lower blood lead levels. [JAMA 2017;317:1244-1251]
Adults with childhood blood lead levels >10 µg/dL also experienced a mean decline of 1.68 IQ points and an absolute mean decline of 0.18 social class scale points from childhood to adulthood, while those with lead levels ≤10 µg/dL experienced a mean increase of 1.22 IQ points (difference, 2.90 IQ points; p<0.001) and 0.12 social class scale points (difference, 0.30 scale points; p=0.02).
“The relationship between childhood lead exposure and downward social mobility by midlife was partially but significantly mediated by cognitive decline following childhood lead exposure,” said the researchers.
After adjusting for covariates, every 5 µg/dL elevation in blood lead levels during childhood was associated with a 1.61-point lower score in adult IQ (p<0.001), a 2.07-point lower score in perceptual reasoning (p<0.001), and a 1.26-point lower score in working memory (p=0.03), as well as a 1.79-unit lower score (p=0.01) in socioeconomic status.
This prospective cohort study comprised 1,037 participants of the Dunedin Multidisciplinary Health and Development Study who were born in Dunedin, New Zealand, between 1972 and 1973, of whom 1,007 were alive at age 38 years. Fifty-six percent (n=565) had their blood lead levels measured at age 11 years (54 percent male, mean blood lead level 10.99 µg/dL).
Ninety-four percent of participants (n=531) had blood lead levels above the normal reference value (5 µg/dL), while 46 percent (n=259) had blood lead levels above the historic international level of concern (10 µg/dL).
According to Bellinger, regular monitoring of lead exposure in children via blood tests, while necessary, is inadequate.
“Reducing the health burden related to lead exposure will require vigorous primary prevention measures ... Environments must be screened, in addition to children, so that the most hazardous sites can be effectively abated before rather than after a child’s exposure occurs,” he said, while stressing the importance of research into “identifying educational interventions that improve the cognitive outcomes of lead-exposed children”.
Focusing on long-term outcomes of lead exposure in childhood meant that the effects of early-life vs later-life lead exposure could not be accounted for, said the researchers, who also recommended that future research involve a more diverse population, as the current one was mainly Caucasian.
They cautioned that the findings may not extend to locations where lead exposure predominantly affects individuals of a lower socioeconomic background and those residing near “former lead-emitting industry sites”.