Exposure to lead during childhood has a negative impact on cognitive function and socioeconomic status three decades on, scientists have shown. It is associated with decline in IQ and downwards mobility from childhood to adulthood.
Lead is a naturally occurring element which has been mined for as long as several millennia and use in a range of products used for human consumption.
In recent years, there has been mounting evidence that lead adversely affects the human body. It appears to be especially harmful to the developing nervous system of children and adolescents. Lead exposure has been found to affect children's cognitive function and behaviours on the short and on the long term.
The study now published in JAMA brings further evidence of this, showing clear changes in IQ and socioeconomic mobility between childhood and midlife.
"I am absolutely certain that lead exposure causes serious and adverse effects on children. An extensive body of work has been published on the subject. It's true that in some of the earlier work, it was hard to separate the harmful effects of lead with other effects of living in poor housing. But robust studies like this one control for these factors, and establish a causal effect", Jessica Wolpaw Reyes, professor of economics at Amherst College, who previously published on the subject, told IBTimes UK.
IQ at age 38
In this new research, the scientists analysed the data of the members of a population-representative 1972-73 birth cohort from New Zealand, which observed participants until the age of 38. A total of 1007 people were still alive at age 38, of whom 565 had been tested for the presence of lead in their blood at the age of 11.
After controlling for factors such as maternal IQ, and IQ and socioeconomic status in childhood, the scientists made a number of significant findings. They established that higher childhood blood levels were associated with lower adult IQ scores nearly three decades later, reflecting cognitive decline following childhood lead exposure.
These lead levels were also associated with lower adult socioeconomic status and with the children seeing their status decline as they reached adulthood.
The scientists also concluded that the link between childhood lead exposure, and downward social mobility by midlife, was mediated by cognitive decline following childhood lead exposure.
"This study is quite well done because it is based on a moderately large sample, representative of the population - the participants were not selected because of concerns of lead exposure, so it is not a biased population. It is also great that they are controlling for early life family and socioeconomic conditions", Wolpaw Reyes commented.
This study adds to a large body of research focusing on the risks associated with lead exposure. it reinforces the message that people should be paying attention to these threats, and should be aware that they can be exposed not only via contaminated water, but also via contaminated soils and paint in their environment.
"This study shows once again the adverse impact of lead exposure on IQ. It suggests that having a good lead policy is the best education policy you can have, as it is an incredibly effective way to help kids", Wolpaw Reyes concluded.