Could Pollution Be Contributing to the Rise in ADHD Diagnoses?
Despite all of the research, the causes of ADHD aren’t fully known. It is generally accepted that ADHD can be inherited; if you have ADHD, there is a good chance that at least one of your parents also have it. But what isn’t understood is whether environmental factors also contribute the rise of ADHD diagnoses over the past decade. A recent study, published in the Public Library of Science Journal, PloS ONE, shows that exposure to pollution while in the womb and in the early years of life might increase the risk of developing ADHD.
ADHD is the most common, chronic condition in children. According to the U.S. Centers for Disease Control and Prevention, the percentage of children in the United States diagnosed with ADHD has risen statistically over the past decade. In 2003, it was estimated that 7.8 percent of children had ADHD, in 2007 that rose to 9.5 percent and in 2011, the number increased to 11 percent. While many experts believe this is due to a better understanding of ADHD, an increased awareness and better detection of the condition, this alone doesn’t fully explain the significant increase. Researchers are looking to see if environmental factors might also contribute to the higher rates of ADHD.
The scientists in the recent study followed 233 pregnant women and their children for nine years. All of the women were either African-American or Dominican and lived in New York City, in areas where air pollution levels are high. Air pollution in urban areas, such as the ones the participants lived in, is caused by traffic, especially diesel fuel exhaust from trucks and buses, and carbon fuels used in residential heating. The levels of Polycyclic Aromatic Hydrocarbons, or PAH, were measured at birth, from samples taken from the placenta and umbilical cord. The children were tested for pollutants via urine tests at three and five years old.
The researchers used standard ADHD screening tests as well as home observations and non-verbal intelligence assessments annually throughout the study period, for example a home assessment and the non-verbal intelligence assessment were completed when the children were three years old.
At the end of the study, researchers found that mothers who were exposed to high levels of PAH during pregnancy were five times more likely to have their child exhibit ADHD symptoms.
Previous studies have shown a correlation between pollution and ADHD, however, this is the first study to look at individuals who are affected by pollution. A study completed in 2013 looked at the overall incidence rate of ADHD in areas high in pollution and found children in high levels of traffic-related pollution were more likely to be diagnosed with ADHD by age seven than those living in areas with low levels of pollution. The authors of this study did indicate that the genetic link to ADHD is much stronger than the link to pollution or other environmental factors.