With millions of American children still at risk for lead poisioning, a new study suggests that the harmful effects could last well into adulthood. 

Research over the past 40 years has linked lead poisoning to developmental delays, cognitive problems, and behavior issues during childhood and the teen years. But the new study, published this week in the Journal of the American Medical Association, is the first to link early lead exposure to problems later in life.

Duke University researchers found that children with elevated blood levels of lead at age 11 had slightly lower IQ test scores and socioeconomic status at age 38 than expected. They also had lower IQ scores and standards of living than peers who were exposed to less lead in childhood.

The study was based on more than four decades of data on 565 children from the small city of Dunedin, New Zealand.

“The study highlights the ongoing burden to society posed by lead. Kids exposed three to four decades ago are still experiencing the adverse impacts,” says Bruce Lanphear, M.D., a children’s environmental health scientist at Simon Fraser University in Canada, who was not involved with this study.

Lead—from sources such as old paint and contaminated soil and water—can be toxic to people at any age. But young children absorb lead more readily, and their still-developing brains are more vulnerable to the effects of lead poisoning.  

Although lead exposure has been sharply reduced over the past few decades—in part due to lead-free gasoline—children in 4 million households across the nation are still being exposed to significant levels of lead, according to the Centers for Disease Control and Prevention (CDC).

The problem goes well beyond the well-publicized water contamination found in Flint, Michigan. A recent Reuters investigation of nationwide lead testing results found that almost 3,000 communities in the U.S. have higher rates of lead poisoning than Flint does. 

And just last week, high blood levels of lead were found in children in dozens of California communities, according to data obtained by Reuters from the California Department of Public Health. 

The Effects on IQ

In the Duke study, researchers compared the subjects' childhood IQ test scores with their adult tests to see if lead exposure had any lingering impact. They found that for every increase in blood lead concentration of 5 micrograms per deciliter (mcg/dL) at age 11, the study participants showed an IQ drop of 1.61 points at age 38.  

Those who were considered to have elevated blood lead levels as children—over 10 mcg/dL—had IQ test scores that were almost 3 points lower than those of their peers as adults.

For most people, the loss of a few IQ points might not significantly change one's intelligence level, explains Aaron Reuben, the Duke graduate psychology student who led the study. But for those already facing cognitive struggles, even a minor reduction in IQ might make it harder to get and keep a job, he says.

Previous research has also shown that small shifts in intellectual ability can add up. One study estimated that the loss of a single IQ point could represent about $18,000 less in lifetime earnings.

“Regardless of where you start out in life, lead exerts a long-term downward pull on cognitive ability and social mobility,” says Reuben.

How to Protect Your Children

In the early 1970s, when the children in the New Zealand study were born, blood lead levels of 11 mcg/dL were typical for children in the U.S.

Thanks to steps like the removal of lead from gasoline and paint, the average U.S. toddler currently has a blood lead level of 1.5 mcg/dl, and less than 1 percent of youngsters have blood lead levels above 10 mcg/dl.

Still, parents should do everything they can to limit their childrens' exposure to lead, says Reuben. Here are some suggestions.

Have your child tested. The effects of lead aren't always obvious, and a simple blood test should be able to tell you if your child has been exposed. The CDC recommends that children at low risk of lead exposure first get tested at age 1, and children at high risk at 6 months. (Some states require lead testing for low-income children between age 1 and 2, but many more who should be screened go untested, says Jennifer Lowry, M.D., a pediatrician in Kansas City, Missouri, and chief of toxicology at Children's Mercy Hospital.) Testing is especially important if you live in a home built before 1978, have water pipes that were installed before 1986, or know or suspect your child has been exposed to lead. If you have any concerns about your child's development or potential lead exposure, talk to your doctor.

Be house-savvy. Lead was removed from house paint in 1978, but old lead-based paint is the most common cause of lead poisoning in children. Test for lead in paint and dust if your home was built before 1978 (home kits may be a reasonable first step to identify lead in the home; if your child tests positive for lead exposure, consider a licensed lead inspector). Keep young children and pregnant women off the premises if it's undergoing renovations, including sanding or scraping paint. Cover or remove chipped or peeling paint, regularly wet-mop floors and window sills, frequently wash children’s hands and toys, and stop them from playing outside in bare soil. Consider professional abatement if lead is found.

Ask about water. Lead can be found in some water pipes in homes built before 1986. If you live in such a home, use cold, not hot, water from the tap for drinking and cooking; hot water is more likely to contain higher lead levels, according to the CDC. Consider having the water in your home tested by a certified laboratory. You can also call your water provider to find out it if the local water supply contains lead. The Environmental Protection Agency can answer questions about lead in drinking water at this hotline

Check for recalled products. Lead has sometimes been found in products such as lipstick, antique toys, dietary supplements, toy jewelry—even, occasionally, imported candy. Keep up with information on products that are recalled because of lead contamination. And, says the CDC, avoid candy imported from Mexico.

Reduce the impact. If your child is found to have high blood levels of lead, get the help you need to find its source and remove it. The effects of lead poisoning on the brain can’t be reversed, but providing an enriching environment can help kids build resilience and mitigate the impact, says Jessica Wolpaw Reyes, P.h.D., a health economist who studies lead exposures at Amherst College in Massachusetts. “Double down on the kind of engagement that fosters cognitive development. Read to them. Speak with them. Bathe their world in language,” she says. Regular consumption of leafy greens, milk, oranges and other foods high in calcium, iron, and vitamin C can also help leach lead out of the body.