April 26, 2017
2 min read

Childhood lead exposure associated with lower IQ, socioeconomic decline in adulthood

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Children in New Zealand exposed to high lead levels exhibited lower cognitive function, socioeconomic status and declines in IQ scores by age 38, highlighting the possible long-term ramifications of lead exposure at young ages.

“Lead is a ubiquitous pollutant. Policies that eliminated lead from paint and gasoline were thought to have eliminated lead from most communities in the developed world,” Aaron Reuben, MEM, from the department of psychology and neuroscience at Duke University, and colleagues wrote. “But the water crisis in Flint, Michigan has triggered renewed concern about lead poisoning. Inhabitants of many U.S. cities are still exposed to high lead levels.”

Lead, a developmental neurotoxin, has uncertain effects on long-term social and cognitive abilities. To examine if there are sustained negative consequences from exposure to the toxin, including cognitive function, socioeconomic status in adulthood, and changes in both IQ and socioeconomic mobility between childhood and adulthood, a population study was designed that included children participating in the Dunedin Multidisciplinary Health and Development Study. Children born between 1972 and 1973 were observed until age 38.

Researchers used the Wechsler Adult Intelligence Scale-IV to assess various measures of children born in the selected cohort at age 38, including IQ, indexes of verbal comprehension, perceptual reasoning, working memory and processing speed. The New Zealand Socioeconomic Indec-2006 was also used to assess socioeconomic status at the same age.

Of the participants who lived to the age of 38 (1,007 of 1,037), 56% were tested for lead at 11 years. At that time, the average blood lead level was 10.99 (4.63) µg/dL. When these individuals reached 38 years of age, their IQ (average = 101.16) and socioeconomic status (average = 49.75) — when adjusted for maternal IQ, childhood IQ and childhood socioeconomic status — was affected by each additional 5 µg/dL of lead.

These negative correlations include IQ adult scores lowered by 1.61 points, perceptual reasoning skills lowered by 2.07 points, and working memory lessened by 1.26 points. Additionally, socioeconomic status was decreased by 1.79. Out of all participants, 40% demonstrated declines in IQ and socioeconomic status from childhood to adulthood, with downward mobility mediated by cognitive weakening beginning in childhood.

“The effect sizes for adult cognitive impairment that were detected are small and do not constitute the extent of impairment that would attract clinical treatment,” the researchers wrote. “They are, however, similar to IQ deficits associated with other notable childhood risk factors, such as very low birth weight. Despite being mild, the cognitive decline evident among lead-exposed children was accompanied by altered socioeconomic life trajectories, measurable as small but detectable downward social mobility by midlife for the most-exposed children regardless of their origins.” — by Katherine Bortz

Disclosure: The researchers report no relevant financial disclosures or conflicts of interest.