A new study suggests that prenatal tobacco exposure and environmental exposure to lead are linked to a third of the estimated two million childhood cases of ADHD. Host Bruce Gellerman talks with Joe Braun, an epidemologist at the University of North Carolina-Chapel Hill and Dr. Bruce Lamphear, director of the environmental health center at Cincinnati Children's Hospital Medical Center.
GELLERMAN: From the Jennifer and Ted Stanley studios in Somerville, Massachusetts - this is Living on Earth. I’m Bruce Gellerman, sitting in for Steve Curwood.
In 1845, Dr. Heinrich Hoffman wrote a poem called “The Story of Fidgety Philip.” Fidgety Philip is a little boy who just can't sit still or control his urges to grab and yell. His behavior sends his parents up the wall. Dr. Hoffman's poem about fidgety Philip is considered the first written description we have of ADHD, attention deficit hyperactivity disorder.
Mental health experts estimate nearly two million kids in the U.S. suffer from ADHD, yet they don't know what causes it. But now, in what's being called a “landmark study” researchers say environmental factors play a major role. That mothers who smoke during pregnancy and preschooler's exposure to lead may account for a third of the cases of attention deficit hyperacivity disorder.
Joining me is the study’s lead author. Joe Braun is an epidemiologist at the University of North Carolina at Chapel Hill. Mr. Braun, welcome to Living on Earth.
BRAUN: Thank you, Bruce it’s good to be here.
GELLERMAN: Also joining us is Dr. Bruce Lamphear, director of the Environmental Health Center at Cincinnati Children's Hospital Medical Center and a national expert on lead poisoning. Dr. Lamphear, welcome to Living on Earth.
LAMPHEAR: Thank you very much, Bruce.
GELLERMAN: Fidgety Philip, he can’t sit still. He wriggles and giggles. He’s really a wild kid. Joe Braun, does this sound like ADHD?
BRAUN: Yes it does, and it reminds me a lot of the kids from when I used to be a nurse at an inner city school it reminds me a lot of the children there who couldn’t sit still. Or children who couldn’t learn because they were too impulsive or they couldn’t concentrate long enough.
GELLERMAN: So, it’s not just fidgeting. These are kids who really have a problem.
BRAUN: Yes, ADHD is characterized by three characteristics. It’s inattention, impulsivity and hyperactivity. The hyperactivity is really the hallmark sign of ADHD and this is what Dr. Hoffman described in 1845. This is their excessive talking, fidgeting, running and climbing excessively when it’s not really appropriate.
GELLERMAN: Let’s talk about your study. You reviewed the medical histories of, what, 4,700 kids?
GELLERMAN: And you were looking specifically at smoking and lead, the role they play in ADHD. What did you find?
BRAUN: Well, what we found in our study is that mothers who smoke during pregnancy, the children of these mothers were at a 2 and a half fold risk for ADHD. We also found children with blood lead levels above 2 micrograms per deciliter were at a 4-fold risk for ADHD.
GELLERMAN: Dr. Lamphear, so what’s the role of lead and where are kids getting exposed to lead?
LAMPHEAR: Old homes contain high concentrations of lead-based paint. And when that paint becomes accessible either through deterioration, remodeling, or renovation, children are exposed primarily through ingestion. And children are most vulnerable during their first 2 years of life. So when a child crawls around on the floor and then sticks their hand in their mouths, what they’re doing is picking up lead particles from the dust, ingesting it, and then absorbing it.
There’s an added whammy and that is that young children, toddlers, seem to be able to absorb lead more efficiently than adults do.
GELLERMAN: Well Mr. Braun, you found correlations between lead levels in kids and ADHD that are much lower than the federal government standard for safety. What you’re suggesting in your article is that the federal government standard is 4 times higher than what you’re finding effects at.
BRAUN: We are finding effects at well below what the government standard is, yes. This isn’t a surprising result in light of some recent research that’s been finding an inverse relationship between children’s blood lead levels and cognition at these low levels. Going from a lead level of zero to ten is associated with anywhere from a 4 to 6 point decrease in IQ.
GELLERMAN: Dr. Lamphear, in the article it’s written that it’s difficult to infer a causal relationship between the disorder and these environmental insults if you will. You have a link but there’s not a causality?
LAMPHEAR: Well that’s correct. It’s very different to infer from observational studies causality. What’s important about this particular paper is for the first time we’ve been able to link lead exposure using blood lead tests with the diagnosis of ADHD. It’s clear that there are many other risk factors that we did not, nor were we able to address. For example, like alcohol intake, like family history of ADHD. I think it’s important for people to know that while we feel fairly confident that prenatal tobacco exposure is indeed a risk factor as is lead exposure, there are still a number of other factors that may increase a child’s risk for having ADHD.
GELLERMAN: Mr. Braum, what do you hope people come away from this study with?
BRAUM: Well, I would hope that this would help persuade policy makers and people on the CDC advisory board to consider once again lowering the action level for blood lead levels. I would also hope that this adds evidence to our vast knowledge of the effects of prenatal tobacco exposure. We know that exposure to tobacco smoke in utero is associated with a whole host of problems ranging from pre-term birth to low birth weight. And I would hope that physicians and other clinicians use this information to work with their patients who are expecting to become pregnant or who are pregnant to quit smoking before they do become pregnant.
LAMPHEAR: This brings up an important point, Bruce and that is that we do change the environment, to alter the environment to make children less likely to start smoking. And we do know that there are things we can do to protect children from lead contaminated hazards in their home. The point is we know what to do and yet as a society, we fail to take those steps to protect kids. Many of the new morbidities of childhood ADHD, learning problems, reading problems, asthma are all linked to, many of them are linked to environmental exposures like tobacco and like lead. And so it shouldn’t surprise us that these new pollutants are at the root of many of the problems we see in children today.
GELLERMAN: Well, Dr. Lamphear, I want to thank you very much.
LAMPHEAR: Thank you very much, Bruce.
GELLERMAN: Dr. Bruce Lamphear is director of the environmental health center at Cincinnati Children’s Hospital Medical Center. And Mr. Joe Braun, thank you.
BRAUN: Thank you.
GELLERMAN: Joe Braun is an epidemiologist at the University of North Carolina at Chapel Hill. Their study, Exposures to Environmental Toxicants and Attention Deficit Hyperactivity Disorder in US children will be published in Environmental Health Perspectives and is available on line. You can find a link to their study at our website loe dot org.
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