Higher exposure of lead in childhood may affect brain health and disrupt cognitive development, researchers say.
Lead is a powerful neurotoxin that can accumulate in a child's bloodstream, then settle in the bones, teeth and soft tissues and build up in the body.
According to the World Health Organization, this toxin can damage the developing nervous system in young children.
The findings, published by JAMA, showed that children with more than 10 micrograms of lead per decilitre of blood at age 11 had 4.25 points lower intelligence quotients at age 38.
For each five-microgram increase in childhood blood lead, a person lost about 1.5 IQ points by age 38, causing lower cognitive function when they were adults.
Further, childhood blood lead level was also associated with lower adult socioeconomic status, reflecting downward social mobility following childhood lead exposure.
"The results indicate that childhood exposures to lead can be linked with cognitive and socioeconomic outcomes detectable more than three decades later," said Aaron Reuben, from Duke University in North Carolina, US.
"Regardless of where you start in life, lead is going to exert a downward pull," added Avshalom Caspi, Professor at Duke University.
Conversely, blood lead levels as low as five micrograms per decilitre may also lower IQ.
For the study, the team included 1,037 participants from New Zealand. Blood-lead tests were conducted for 565 of them at age 11.