(CNN) — A history of lead in gasoline may be behind tens of millions of mental health conditions in the United States, according to new research.

“We’ve shifted the curve in the population for mental health problems, so that everyone has a greater liability in the mental illness symptoms, and that some people who were already at risk are going to develop diagnosable disorders sooner, more often or more kinds,” said coauthor of the study Dr. Aaron Reuben, assistant professor of clinical neuropsychology at the University of Virginia.

The study published Wednesday in The Journal of Child Psychology and Psychiatry estimates that about 151 million mental disorder diagnoses in the US are attributable to lead. The exposure likely would not have happened had lead not been in gasoline, Reuben added.

Cars ran on gasoline containing lead starting in the 1920s, and the US did not start phasing out the substance until the 1980s, after substantial evidence of harm over the decades, according to the US Energy Information Administration. Leaded gasoline continues to fuel some planes, race cars, and farm and marine equipment.

“The people who were exposed are not in the history books,” Reuben said. “Millions of Americans are walking around with an unknown, invisible history of lead exposure that has likely influenced for the worse how they think, feel and behave.”

How lead impacts the body

Scientists have accumulated research over the last century showing that lead is harmful to almost every organ system, Reuben said.

In a previous study, he and a team used data on childhood blood-lead levels, leaded gas use, and population statistics to estimate childhood lead exposure and found that half of the US population were exposed to adverse levels of lead early in life.

The number of people impacted might be unexpected to many people, said Dr. Bruce Lanphear, a population health scientist at Simon Fraser University in Canada with expertise in lead poisoning. He was not involved in the research.

“Given their caveats and limitations, I think they’ve done a thorough job of trying to estimate exposures,” he said.

One such limitation was that researchers did not measure all possible exposure sources, meaning that the results may actually underestimate the problem, Lanphear added.

“We have not been able to fully understand how those exposures influenced health and disease across the century,” Reuben added.

Lead is a potent neurotoxin and can disrupt brain development in many ways that can impact most types of mental health problems, including anxiety, depression and ADHD, he said. But people were also likely impacted in ways that cannot be diagnosed.

“It also changed personalities. We believe that (lead exposure) makes people a little less conscientious –– so less well organized, less detail-oriented, less likely to be able to pursue their goals in an organized way, and more neurotic,” Reuben added.

Millions of homes still contain lead

If lead exposure is a widespread problem and the possible health impacts are serious, what can be done?

The first step Reuben recommends is to educate yourself on the sources of lead exposure.

“We completely phased lead out of gasoline in ’96, we phased lead out of pipes in ’86, and we took it out of paint in ’78,” he said. “If you’re living in a home that was built before those years, you should be aware that there is likely a lead hazard in your soil or your home.”

It doesn’t mean it is time to move out of your older home, just that you should check for lead when doing renovations or disturbing the soil, Reuben said.

“The (Environmental Protection Agency) recently lowered its soil screening level, and it means that possibly one in four households in the US has soil lead that would now be deemed potentially hazardous,” he added.

You can test for lead exposure ­­–– Reuben requests tests for his kids at the pediatrician, he said.

For those that have already been exposed, there isn’t a definitive answer on whether you can reduce your levels of lead, but Reuben recommends taking steps to identify the sources and reducing future exposure. You can also limit harm from the lead by doing other things that promote health like exercising, eating a nutritious diet and cutting out alcohol and cigarettes, he said.

But the most impactful step will be for institutions to invest in research and the elimination of lead from the environment, Lanphear said.

“We really need regulatory agencies like the FDA to make sure there’s not lead in the baby food,” he said. “Finding ways to deal with the 20 million homes that still contain lead hazards, getting rid of leaded aviation fuel, these are not things that people can do. This is what the government and regulatory agencies need to do.”

“We’ve got to stop putting this burden on people and families,” Lanphear added.