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Lead’s Latent Effects

Although children in North America are exposed to less lead than children 30 years ago, the lead problem has not disappeared. Lead exposure in inner-city and certain minority populations remains a serious problem. Depending on the intensity of exposure and the age of the exposed person, lead can cause developmental problems, mental retardation, stunted growth, and fertility problems.

Add to that a potential new effect of lead exposure: an increased risk of Alzheimer’s Disease. University of Rhode Island neurologist Nasser Zawia and colleagues have published a study in the Journal of Neuroscience, pointing to an association between lead exposure in infancy and Alzheimer’s in adulthood.

“People mostly think of lead exposure as being something that only affects children, and nobody has been studying the elderly and adults to see if they’re impacted,” says Zawia. But by studying monkeys exposed to low lead levels in 1980 and 1981, Zawia and his team found evidence that childhood lead exposure could trigger growth of brain plaques associated with Alzheimer’s Disease.

“What we found was simply, in the monkeys that were exposed to lead as infants, there was an increase in the expression of the genes involved in Alzheimer’s Disease and the proteins that are part of the core of the plaques,” Zawia explains.

Looking for an association between lead exposure and Alzheimer’s Disease requires a long-term study of primates. In the early 1980s, as part of a different study, a group of infant monkeys was systematically exposed to infant formula that contained lead levels considered safe for children at the time. (Since then, the Center for Disease Control and Prevention has lowered the maximum acceptable blood lead level.)

The National Institutes of Health happened to keep the post-mortem brain tissue and DNA samples from the monkeys from the earlier study, and Zawia’s team was able to analyze the samples from the NIH. When they looked at the material from the monkeys, the researchers found that “every single one of them had the same pattern of increased plaques and of dense plaques,” Zawia says.

Columbia University lead poisoning expert Joseph Graziano, who did not participate in the monkey research, describes Zawia’s findings as “a call for more research” about whether lead may cause Alzheimer’s Disease in humans.

“The finding is important in that lead probably is one of many environmental exposures that may contribute to Alzheimer’s Disease,” Graziano says. He adds that if a link between lead and Alzheimer’s Disease does bear out in people, it could mean that people exposed to relatively low levels of lead years ago may be at risk.

“Many, many Americans had blood leads in those ranges as children. Lead exposure in the United States peaked at 1977. Plenty of us had blood leads in that range and thought nothing of it at the time,” he says.

According to Zawia, the study is further evidence that “we shouldn’t assume just removing a substance from the environment means that everything will be okay. So we have to be much more vigilant, and we have to learn more how to protect ourselves” from hazardous materials like lead.

Zawia’s lab is looking into both causes and treatments for Alzheimer’s Disease. He says new tools like blood screening for past lead exposure could help the right people to seek help.

Research authors: Jinfang Wu, Riyaz basha, Brian Bock, David Cox, Fernando Cardozo-Pelaez, Christopher McPherson, Jean Harry, Deborah Rice, Bryan Maloney, Demao Chen, Debomoy Lahiri, and Nasser Zawia.

Publication: Journal of Neuroscience on January 2, 2008

Funding: National Institutes of Health (NIEHS and NIA), the University of Rhode Island INBRE Core Facility and the Alzheimer’s Association.

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