Attention deficit hyperactivity disorder takes a huge toll on children, with about 9 percent of kids ages 8 to 15 displaying diagnosable symptoms of inattention, hyperactivity, and impulsive behavior that can make schoolwork an ordeal and friendships trying. Maternal smoking and lead exposure in early childhood might be behind nearly 40 percent of ADHD cases, according to new research. If that turns out to be true, it may be possible to prevent many cases of ADHD and reduce the huge social, financial, and personal toll of the disorder.
While the cause (or, most likely, causes) of ADHD remains a mystery, we do know that it tends to run in families, so there's probably a genetic susceptibility. In addition, prenatal exposure to tobacco smoke and industrial chemicals and childhood exposure to lead have long been associated with attention problems and impulsivity. Both lead and tobacco alter how the brain uses the neurotransmitter dopamine, which helps control movement and emotion, and the brains of people with ADHD may be less sensitive to dopamine.
What's important about this new information, from researchers at Cincinnati Children's Hospital Medical Center, is that it is based on a big national survey—covering 2,588 children ages 8 to 15—and is the first to measure how maternal smoking and lead exposure combine to affect ADHD. Being exposed to both tobacco in the womb and lead in childhood is a double whammy; 28.6 percent of children who were exposed to prenatal maternal smoking and the upper third of lead exposure levels had ADHD, compared with 5.2 percent of children with the lowest blood lead levels and no maternal smoking. The researchers, whose work was published online in Pediatrics, estimate that 38 percent of ADHD cases could be caused by maternal smoking, lead exposure, or both.
Here's how to reduce the risk of tobacco and lead exposure in your own children:
- Don't smoke. This info provides yet another great reason to never start smoking, or to quit right now if you're a mom or contemplating being one. Also, don't drink alcohol or abuse drugs while pregnant. They may reduce the activity of neurons that produce neurotransmitters in the brain. Secondhand smoke wasn't implicated in this latest study, but there's tons of evidence that living with a smoker increases a child's risk of asthma and other chronic diseases. So don't smoke.
- Avoid PCBs and other environmental toxins while pregnant. Exposure to the industrial chemical polychlorinated biphenyl (PCB) while pregnant has been linked to increased rates of ADHD. PCBs were banned starting in 1979, but they persist in the environment.
- Make sure your home is free of lead and other environmental toxins. Lead exposure lowers IQ and causes behavioral problems in children who are exposed in early childhood because it interferes with brain development. Researchers increasingly believe that lead has more subtle effects at much lower doses than the level used as the threshold in state-mandated testing for lead poisoning. The most common sources of lead contamination are lead paint in buildings built before 1978, dust from that paint, and soil contaminated outside buildings painted with it. The Environmental Protection Agency's National Lead Information Center provides information about testing homes and soil for lead, and states provide information on lead testing and abatement contractors. (Here's Michigan's page on reducing risks of lead in the home, and here is the EPA's take on reducing lead risk.)
- Have children tested for blood lead levels. Pediatricians are required by some states to test young children for lead at 12 months of age and then again at 24 months. Children who live in neighborhoods with lots of old housing are more likely to be exposed. A level less than 10 micrograms per deciliter is thought to indicate no lead poisoning and is the standard used in state-mandated test. But the children in the Cincinnati study had an increased risk of ADHD at 1.3 micrograms or greater per deciliter. So the testing level may not be set low enough to prevent ADHD.
- Hand washing and healthy eating help, too. Young children are exposed to lead in the environment by touching contaminated dust or dirt, then touching their mouths. Hand washing helps reduce that risk. So does eating foods rich in calcium and iron; they reduce the amount of lead a child's body absorbs.
How panicked should parents be? That's the big question. Avoiding smoking is a no-brainer; every parent or would-be parent needs to stop now, for the sake of their own health as well as their children's. "Clearly the safest environment for a child to grow up in is void of lead and smoke exposure," said Paul Lipkin, director of the Center for Development and Learning at Kennedy Krieger Institute in Baltimore. Parents can check back with their pediatrician to see what the child's blood lead levels were if they are concerned about lead exposure, Lipkin said, and also follow HUD guidelines for reducing lead in the home.
But protecting children from brain-damaging lead exposure is tough. We had our 52-year-old house tested for lead paint when our daughter was born and were relieved to find that there was very little. We've tried to follow EPA guidelines on keeping lead paint undisturbed (it's covered with newer latex paint) and eating healthfully. Our pediatrician has also performed scheduled blood lead tests. Did we do enough? I don't know. But no child should have to suffer needlessly. If this new research spurs public-health officials and lawmakers to ramp up efforts to protect children from lead and get moms to quit smoking, then that may be the best news ever for ADHD.