Childhood Exposure To Lead May Lead To Lower IQ In Later Life

Childhood exposure to lead could affect adults decades later, a long-term study of more than 500 New Zealand children who grew up in the era of leaded gasoline has shown. The research suggests an association between early childhood lead exposure and a reduction in later life socioeconomic status and cognitive ability.

Although the reported effects are slight, they are significant, and demonstrate that the higher the blood lead level in childhood, the greater the loss of IQ points and occupational status in adulthood.

Data for the study came from a life-long examination of more than 1,000 people born in Dunedin, New Zealand in 1972 and 1973. During their childhood, New Zealand had some of the highest gasoline lead levels in the world.

Senior author Terrie Moffitt, Duke University professor of psychology & neuroscience and psychiatry & behavioral sciences, said:

“This is historical data from an era when lead levels like these were viewed as normal in children and not dangerous, so most of our study participants were never given any special treatment.”

Lead Testing

From birth to adulthood, the study participants have been regularly tested for cognitive skills like perceptual reasoning and working memory. At age 11, blood samples were collected from 565 of them which, were then tested for lead.

Individuals who were found to have over 10 micrograms of lead per deciliter of blood at age 11 had IQs at age 38 that were, on average, 4.25 points lower than their less lead-exposed peers. They were also found to have lost IQ points relative to their own childhood scores.

blood lead level results

People screened for blood-lead level at age 11 and IQ-tested in childhood and at age 38, reveal an association between childhood lead exposures and a decline in IQ. Higher doses led to greater losses. Adapted from: JAMA, 2017;317(12):1-8

The study found that for each 5-microgram increase in blood lead, a person lost around 1.5 IQ points.

“This case is different from the one in Flint, Michigan and other cities where lead in the drinking water has led public health officials to begin special interventions for those children,” Moffitt said.

Flint’s children are receiving regular blood monitoring and expanded early childhood education, behavioral health services and special nutrition with the federal government’s support.

“Interventions of this sort are intended to forestall the sorts of effects we’ve measured in this study,” she said.

Level Of Concern

The mean blood lead level of the children at age 11 was 10.99 micrograms per deciliter of blood, slightly higher than the historical “level of concern” for lead exposure. Today’s reference value at which the CDC recommends public health intervention is half that, 5 micrograms per deciliter, a level which 94 percent of children in the study exceeded.

A safe blood lead level in children has not been established. Leaded gasoline was phased out in the U.S. and New Zealand between the mid-1970s and the mid-1990s, but is still used in some Asian and middle eastern countries.

Study first author Aaron Reuben, a Duke psychology graduate student, said:

“The downward social mobility we see mirrors the trend in IQ. The decline in occupational status is partially but significantly explained by the loss of IQ. If you’re above the historic level of concern (for lead exposure), you’re doing worse on both. The cognitive deficits associated with lead persisted for decades, and showed in the kinds of occupations people got.”

The childhood social status of each child’s family was compared to their adult standing at age 38. Children who were over 10 micrograms of lead attained occupations with socioeconomic status levels four-tenths lower than their less-exposed peers.

Aaron Reuben, Avshalom Caspi, Daniel Belsky, Jonathan Broadbent, Honalee Harrington, Karen Sugden, Renate Houts, Sandhya Ramrakha, Richie Poulton, Terrie Moffitt
Association of Childhood Blood Lead Levels With Cognitive Function and Socioeconomic Status at Age 38 Years and With IQ Change and Socioeconomic Mobility Between Childhood and Adulthood
JAMA. 2017;317(12):1244-1251. doi:10.1001/jama.2017.1712

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