ADHD linked to air pollutants

Children have an increased risk of attention problems, seen as early as grade school, if their moms inhaled a certain type of air pollution when they were pregnant. That’s the finding of a new study. Released when things don’t burned completely, this pollution is known as polycyclic aromatic hydrocarbons, or PAHs. The biggest sources of these PAHs:  the burning of fossil fuels, wood and trash.

Frederica Perera works at Columbia University’s Mailman School of Public Health in New York City. She researches how exposure to things in the environment affects children’s health. In a new study, she and her team studied the exposure to air pollution of 233 nonsmoking pregnant women in New York City. Because burning tobacco can spew PAHs into the air and lungs, Perera’s team focused on nonsmokers. The researchers wanted to probe other sources of PAHs, ones that would have been hard for an individual to avoid.

The team started by testing the blood of each woman during pregnancy. The reason: Any PAHs in a woman’s blood would also be available to the baby in her womb. Nine years later, the researchers investigated signs of attention problems in those children, now age 9. They asked each child’s mother a series of questions. These included whether her child had problems doing things that needed sustained mental effort, such as homework or games with friends. The scientists also asked if the kids had trouble following instructions or made frequent, careless mistakes.

All of these can be symptoms of a disorder called Attention Deficit Hyperactivity Disorder, or ADHD. About one in 10 U.S. children has ADHD.

Among the women studied, traffic and home heating were the primary sources of air pollution exposure, Perera and her team suspect. Some of these women had low levels of PAHs in their blood. Others had high levels. Those with high levels were five times as likely to have children who showed attention problems by age 9. The new findings were published November 5 in the journal PLOS ONE.

Not all ADHD is the same

There are three types of ADHD. The first is known as inattentive ADHD. Children with this type have a hard time focusing. They can become distracted and disorganized easily. Children with the second type are hyperactive. They fidget, move around a lot and have a hard time controlling other behaviors. A third type shows both sets of symptoms.

Children in the study who were exposed in the womb to high levels of PAHs mostly had the first type of ADHD, Perera says. This suggests exposure to PAHs in the air may be connected to childhood ADHD, she concludes. The finding worries her because other studies have shown children with ADHD have problems in school, with making friends and with keeping jobs later in life.

Little is known about what causes ADHD. But scientists suspect both genes — traits inherited from someone’s parents — and exposure to certain pollutants play roles.

“One possible way in which PAH could affect the developing brain is by impacting the endocrine system,” says Perera. This is the system that controls hormones in our bodies. Hormones are vitally important. They help control what happens in our body’s cells. It is also possible that “PAHs could be damaging DNA or how DNA functions,” Perera points out. DNA is the blueprint for genes, which tell our bodies how to grow and function.

The new study is the first to explore links between exposures to PAHs early in life and a child’s later development of ADHD.

Pregnant women can limit their exposure to indoor sources of PAHs by asking people not to smoke in their homes, says Perera. But PAHs from traffic and home heating are harder to avoid.

David Bellinger is an expert in environmental health. He works at Harvard University in Boston, Mass. The study by Perera’s team, he says, shows how important it is for communities to reduce air pollution “so that the brains of our children are better protected.”

Power Words

attention deficit hyperactivity disorder  (ADHD) This is a disorder characterized by not being able to focus or pay attention, being physically overactive, not being able to control behavior, or a combination of these.

behavior  The way a person or other organism acts toward others, or conducts itself.

DNA  (short for deoxyribonucleic acid) A long, double-stranded and spiral-shaped molecule inside most living cells that carries genetic instructions. In all living things, from plants and animals to microbes, these instructions tell cells which molecules to make.

endocrine system  The hormones (chemicals secreted by the body) and the tissues in which they turn on (or off) cellular action. Medical doctors who study the role of hormones in health and disease are known as endocrinologists. So are the biologists who study hormone systems in nonhuman animals.

fossil fuels  Any fuel — such as coal, petroleum (crude oil) or natural gas —  that has developed in the Earth over millions of years from the decayed remains of bacteria, plant or animals.

gene  (adj. genetic) A segment of DNA that codes, or holds instructions, for producing a protein. Offspring inherit genes from their parents. Genes influence how an organism looks and behaves.

hormone  (in zoology and medicine)  A chemical produced in a gland and then carried in the bloodstream to another part of the body. Hormones control many important body activities, such as growth. Hormones act by triggering or regulating chemical reactions in the body. 

hydrocarbons  Any of a range of large molecules created by chemically bound carbon and hydrogen atoms. Crude oil, for example, is a naturally occurring mix of many hydrocarbons.

polycyclic aromatic hydrocarbons  (or PAHs)  A family of combustion by-products, many of which are quite toxic.