Childhood Lead Exposure Tied To Midlife Brain Structural Integrity

Higher childhood blood lead levels are associated with lower structural brain integrity decades later, a new study suggests.

Researchers examined data on 564 children born in New Zealand in 1972 and 1973 who had blood lead levels measured at age 11 years, and had MRIs to assess structural brain integrity at age 45.

Mean childhood blood lead levels were 10.99 ug/dL and levels ranged from 4 to 31 ug/dL. Overall, 258 participants (46%) had childhood blood lead levels higher than 10 ug/dL, the historical level of concern, and 530 (94%) had childhood blood levels above 5 ug/dL, the current level of concern.

By age 45, MRIs showed that adults had mean cortical thickness of 2.6 mm, mean total cortical surface area of 186.5 square centimeters (cm2), and mean bilateral hippocampal volume of 8.7 cubic centimeters (cm3).

Each 5 ug/dL increase in childhood blood levels was significantly associated with a 1.19 cm2 smaller cortical surface area and a 0.10 cm3 smaller hippocampal volume at age 45, as well as a 2.07-point lower IQ score and a BrainAGE index score 0.77 years older.

"Our findings are relatively modest - lead exposure, at low levels, will not be the primary determinant of a person's overall brain health, development, or aging," said lead study author Aaron Reuben of the Department of Psychology and Neuroscience at Duke University in Durham, North Carolina.

"But we do find that childhood lead exposure exerts a downward pull on brain integrity and cognitive function well into midlife, so that people on the cusp of low functioning or problems may experience them sooner than they otherwise would," Reuben said by email.

The study didn't find a significant association between self-reported cognitive function at age 45 and childhood blood lead levels. There also was no significant association between childhood blood lead levels and mean cortical thickness in adulthood.

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The model adjusted for sex, maternal IQ, and childhood socioeconomic status. And there was no significant socioeconomic gradient in lead exposure, the authors note in JAMA.

Still, one limitation of the study is that it only examined one cohort in a single country, and results might not be generalizable to other populations, the study team notes. The researchers also lacked data on cumulative lead exposure.

Much of the impact lead exposure has on brain development and function during childhood and beyond is driven by factors such the timing, dosage, and duration of exposure as well as the route of exposure, said Travis Beckwith, a researcher in the Department of Environmental and Public Health Sciences at the University of Cincinnati College of Medicine in Ohio.

"Generally speaking, the greater the amount and the longer the duration of lead exposure, the higher the risk for adverse outcomes," Beckwith, who wasn't involved in the study, said by email.

The study results suggest that lead exposure in childhood can have profound and lasting effects on the brain and offers fresh evidence of the importance of preventing this exposure, said Dr. Brian Schwartz, a professor of environmental health and engineering, epidemiology and medicine at the Johns Hopkins Bloomberg School of Public Health in Baltimore.

The results also suggest that people with a history of lead exposure may need monitoring and intervention as they age, Dr. Schwartz, who wasn't involved in the study, said by email.

"We must prevent lead exposure in children," Dr. Schwartz said. "Regarding persons in mid- to late-life now, who had exposure to lead earlier in life, the findings suggest we need to learn more about how to minimize the later impacts of this earlier lead exposure, and how to minimize the cognitive impacts, impacts on daily activities, and risk of dementia that these persons may be at higher risk for as they age."

—Lisa Rapaport

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