Attention-deficit hyperactivity disorder (ADHD) is one of the most common childhood conditions, affecting 11 percent of U.S. kids in 2012. Diagnoses of the condition have increased 42 percent since 2004, according to the Centers for Disease Control and Prevention (CDC), and by 4 years old, some kids are already taking prescription drugs. While many cases of ADHD may be diagnosed incorrectly, researchers looking at why there’s been such an increase have another suggestion: air pollution.
In a study published in the journal PLOS One, researchers at Columbia University’s Mailman School of Public Health found that air pollution in its own neighborhood, New York City, may be contributing to a rise in the number of children with ADHD. The findings are of particular significance for low-income groups and minorities, who are at an increased risk of exposure to the pollutants studied, which are known as polycyclic aromatic hydrocarbons (PAHs).
“This study suggests that exposure to PAH encountered in New York City air may play a role in childhood ADHD,” said lead author Dr. Frederica Perera, director of the school’s Center for Children’s Environmental Health, in a press release. “The findings are concerning because attention problems are known to impact school performance, social relationships, and occupational performance.”
Aside from possibly contributing to the development of ADHD, exposure to PAHs has been linked to birth defects, behavioral problems in kids, kidney and liver damage, cataracts, and various cancers. The organic compounds are found in almost every aspect of our lives — from vehicle exhaust and tobacco smoke to grilled meat (it’s a product of charring) and medicines — so unfortunately, there’s no getting away from them. However, it’s become increasingly clear that we should all be making efforts to minimize our exposure.
In this latest study, the Columbia University researchers followed 233 pregnant NYC women over the course of their pregnancies, and throughout the majority of their children’s early lives. During this time, they also took blood and cord samples from the mothers (shortly after birth) and urine samples from the kids at ages 3 and 5 (to test for PAH metabolites).
After evaluating the kids for ADHD, the researchers found that children whose mothers were exposed to higher levels of PAHs during pregnancy were five times more likely to develop ADHD. Of the 33 exposed to high levels, 13 developed the hyperactive-impulsive subtype of ADHD, while seven had the inattentive subtype, and 13 had both.
Though it’s not entirely clear how pollution contributes to the condition, the researchers suggested in their paper that it could be due to oxidative stress, a disruption in the endocrine system, DNA damage, or issues with placental growth, which could have led to reduced oxygen and nutrient intake. “During the fetal period and early childhood years, the brain is rapidly developing and vulnerable to neurotoxic insults that may manifest as adverse outcomes in childhood and adulthood,” the researchers wrote.
Not all exposure to PAHs is the same, however, and minorities and low-income groups are particularly vulnerable, the researchers pointed out. “Urban, minority populations in the U.S. often have disproportionate exposure to air pollution and are at greater risk for adverse health and developmental outcomes from this exposure,” they wrote. What’s more, the adverse impact of air pollution on the developing brain can actually contribute to the cycle of poverty, according to an earlier study from Columbia University researchers, who found that, among low-income children, IQ-loss associated with exposure to air pollution can have significant long-term financial consequences, including lower lifetime earnings.
That link between socioeconomic status and air pollution exposure has been demonstrated in other studies, as well: earlier this year, researchers from the University of Minnesota (UM) found that throughout the country, even in the most rural states and cleanest cities, low-income minorities were more likely to live around high levels of PAHs and, as a whole, breathe in more pollution than whites — findings that one of the researchers told the Washington Post “likely have health implications.”
Generally, researchers and advocates point to two processes that contribute to large racial gaps like the one uncovered in the UM study. On the one hand, energy companies tend to choose low-income communities of color to site environmental hazards, because it’s the cheapest and easiest thing to do. On the other, when a power plant does move into town and property values drop, white inhabitants have a tendency to flee. Each cycle reinforces the other.
A threat to public health
The researchers said that more research is needed to determine how much pollution contributes to ADHD. If they’re able to determine that environmental factors are to blame, even partially, they may be able to work toward prevention methods. Until then, however, we’re going to have to rely on “currently available pollution controls, greater energy efficiency, the use of alternative energy sources, and regulatory intervention,” they wrote.
While the link between pollutants and ADHD is not yet fully understood, it is clear that air pollution is harmful to children’s developing brains. Other studies have shown an increased risk of autism, schizophrenia, and brain inflammation among children exposed to high levels of environmental pollutants. Air pollution has also been tied to serious health impacts in adults. Long-term exposure has been linked to kidney damage, stroke, heart attack, irregular heart rhythms and death.
These severe health effects were one of the primary motivations for the Environmental Protection Agency’s new plan to reduce carbon emissions from power plants, which the agency proposed this summer. The plan was met with applause from leading public health organizations, including the American Public Health Association (APHA), who called the EPA proposal a “critical and necessary step for ensuring greater health now and for future generations.”
“Today’s EPA proposal does something unprecedented: guaranteeing lower levels of carbon emissions, which will reduce threats to public health. The proposal will cut carbon pollution, smog and soot, and in its first year will prevent up to 100,000 asthma attacks and 2,100 heart attacks,” APHA Executive Director Dr. Georges Benjamin, MD, said in a statement. “Thanks to EPA’s proposed standards we will reduce these threats and provide all Americans with safer air, cleaner energy and a more stable climate.”