Summary: A new study looks at the long term ramifications of childhood lead exposure, finding links to lower cognitive function, IQ and socioeconomic status.
Leaded gasoline creates a natural experiment in long-term study.
A long-term study of more than 500 children who grew up in the era of leaded gasoline has shown that their exposure to the powerful neurotoxin may have led to a loss of intelligence and occupational standing by the time they reached age 38.
The effects are slight, but significant, showing that the higher the blood lead level in childhood, the greater the loss of IQ points and occupational status in adulthood. The study appears Wednesday in the Journal of the American Medical Association.
Study participants are part of 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.
From birth to adulthood, these people have regularly been assessed for cognitive skills such as perceptual reasoning and working memory. At age 11, blood samples were collected from 565 of them which were then tested for lead.
Participants who were found to carry more than 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.
The study found that for each 5-microgram increase in blood lead, a person lost about 1.5 IQ points.
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. No safe blood lead level in children has been identified.
“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,” said Terrie Moffitt, the senior author of the study and Duke’s Nannerl O. Keohane University Professor of psychology & neuroscience and psychiatry & behavioral sciences.
“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.
What makes the New Zealand case an important natural experiment is that automobile traffic goes through all neighborhoods. Unlike exposures to leaded paint or lead pipes in older structures, which pose more of a threat to poorer families, the exposure to leaded gasoline fumes was distributed relatively evenly across all social strata.
Beginning in the 1920s, a compound called tetra-ethyl-lead was added to gasoline for its ability to boost octane ratings and raise engine power. The lead itself didn’t burn however, and emerged from tailpipes as elemental lead and lead oxides which settled as a particulate in soils around areas where cars were common.
Soil hangs on tightly to lead particles and soils next to busy roads have been found to have the highest lead concentrations from the leaded gasoline era. Children playing outside were prone to either breathe in lead-laden dust, or swallow small amounts of leaded soil.
In either case, lead can accumulate in the child’s bloodstream. It then settles into the bones, teeth and soft tissues and accumulates in the body over time.
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.
“Regardless of where you start in life, lead is going to exert a downward pull,” said Avshalom Caspi, Edward M. Arnett Professor of psychology & neuroscience and psychiatry & behavioral sciences at Duke, who is a co-author on the paper. A neurotoxin exposure that affects all parts of society relatively equally would move the entire curve of IQ and social status downward. “If everyone takes a hit from environmental pollutants, society as a whole suffers.”
The study also compared changes in social standing using a measure from the New Zealand government that plots families on a 6-point scale. 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.
“The downward social mobility we see mirrors the trend in IQ,” said Aaron Reuben, a Duke psychology graduate student who is first author on the study. After various statistical controls were applied to the data, “the decline in occupational status is partially but significantly explained by the loss of IQ,” he said. “If you’re above the historic level of concern (for lead exposure), you’re doing worse on both.”
The effects of lead exposure are probably long-lasting as well, Reuben added. “The cognitive deficits associated with lead persisted for decades, and showed in the kinds of occupations people got.”
Funding: The Dunedin Multidisciplinary Health and Development Research Unit is supported by the New Zealand Health Research Council and New Zealand Ministry of Business,
Innovation and Employment (MBIE). This research received support from U.S. National Institute on Aging grants R01AG032282, R01AG049789, R01AG048895, the U.K. Medical Research Council grant MR/P005918/1, the Economic and Social Research Council grant ES/M010309/1, and the Jacobs Foundation.
Source: Karl Leif Bates – Duke
Image Source: NeuroscienceNews.com image is credited to Duke University from JAMA, 2017;317(12):1-8.
Original Research: Abstract for “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” by Aaron Reuben, Avshalom Caspi, Daniel Belsky, Jonathan Broadbent, Honalee Harrington, Karen Sugden, Renate Houts, Sandhya Ramrakha, Richie Poulton, and Terrie Moffitt in JAMA. Published online March 28 2017 doi:10.1001/jama.2017.1712
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
Importance Many children in the United States and around the world are exposed to lead, a developmental neurotoxin. The long-term cognitive and socioeconomic consequences of lead exposure are uncertain.
Objective To test the hypothesis that childhood lead exposure is associated with cognitive function and socioeconomic status in adulthood and with changes in IQ and socioeconomic mobility between childhood and midlife.
Design, Setting, and Participants A prospective cohort study based on a population-representative 1972-1973 birth cohort from New Zealand; the Dunedin Multidisciplinary Health and Development Study observed participants to age 38 years (until December 2012).
Exposures Childhood lead exposure ascertained as blood lead levels measured at age 11 years. High blood lead levels were observed among children from all socioeconomic status levels in this cohort.
Main Outcomes and Measures The IQ (primary outcome) and indexes of Verbal Comprehension, Perceptual Reasoning, Working Memory, and Processing Speed (secondary outcomes) were assessed at age 38 years using the Wechsler Adult Intelligence Scale–IV (WAIS-IV; IQ range, 40-160). Socioeconomic status (primary outcome) was assessed at age 38 years using the New Zealand Socioeconomic Index-2006 (NZSEI-06; range, 10 [lowest]-90 [highest]).
Results Of 1037 original participants, 1007 were alive at age 38 years, of whom 565 (56%) had been lead tested at age 11 years (54% male; 93% white). Mean (SD) blood lead level at age 11 years was 10.99 (4.63) µg/dL. Among blood-tested participants included at age 38 years, mean WAIS-IV score was 101.16 (14.82) and mean NZSEI-06 score was 49.75 (17.12). After adjusting for maternal IQ, childhood IQ, and childhood socioeconomic status, each 5-µg/dL higher level of blood lead in childhood was associated with a 1.61-point lower score (95% CI, −2.48 to −0.74) in adult IQ, a 2.07-point lower score (95% CI, −3.14 to −1.01) in perceptual reasoning, and a 1.26-point lower score (95% CI, −2.38 to −0.14) in working memory. Associations of childhood blood lead level with deficits in verbal comprehension and processing speed were not statistically significant. After adjusting for confounders, each 5-µg/dL higher level of blood lead in childhood was associated with a 1.79-unit lower score (95% CI, −3.17 to −0.40) in socioeconomic status. An association between greater blood lead levels and a decline in IQ and socioeconomic status from childhood to adulthood was observed with 40% of the association with downward mobility mediated by cognitive decline from childhood.
Conclusions and Relevance In this cohort born in New Zealand in 1972-1973, childhood lead exposure was associated with lower cognitive function and socioeconomic status at age 38 years and with declines in IQ and with downward social mobility. Childhood lead exposure may have long-term ramifications.
“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” by Aaron Reuben, Avshalom Caspi, Daniel Belsky, Jonathan Broadbent, Honalee Harrington, Karen Sugden, Renate Houts, Sandhya Ramrakha, Richie Poulton, and Terrie Moffitt in JAMA. Published online March 28 2017 doi:10.1001/jama.2017.1712