Air pollution slows brain development: study

Air pollution takes a double toll on babies' brains

Studies have tied air pollution to a wide range
of problems in children.

A common pollutant in vehicle exhaust, power plant emissions and cigarette smoke can shrink white matter in fetal brains and cause developmental damage during the toddler years, a new study suggests.

In 40 children examined by researchers, prenatal exposure to polycyclic aromatic hydrocarbons was correlated with reduced white matter on the left side of children's brains during their early childhood.

Those physical changes in the brain's internal wiring also were correlated with slower cognitive processing and with symptoms of attention deficit and hyperactivity, according to the study published in the journal JAMA Psychiatry.

“They tend to be fidgety and hyperactive and very impulsive, so they leap before they look,” said Dr. Bradley Peterson, director of the Institute for the Developing Mind at Children's Hospital Los Angeles and the lead author of the report.

The researchers had previously tied behavioral and cognitive problems to eight common types of these pollutants, which are a product of incomplete combustion of organic materials.

The new study now suggests those problems have a biological root in the altered architecture of the brain.

The research involved 655 New York City women of Dominican and African American descent who gave birth between 1997 and 2006.

During late pregnancy, the women carried detector backpacks that measured exposure to PAHs over 48 hours. Their children later were tested for exposure and underwent several rounds of cognitive and behavioral testing.

For the JAMA Psychiatry study, Peterson and his colleagues selected a representative sample from the original study group: 20 children whose own PAH readings were below the median and 20 whose PAH levels were above it.

All the children were about 8 years old when they underwent magnetic resonance imagery scans.

Those scans showed that white matter was significantly reduced from normal volumes throughout the left hemisphere, an area that controls language and cognition, among other higher functions.

In fact, the higher their prenatal exposure to PAH was, the more white matter was reduced and the more acute the behavioral and developmental problems were, the study found.

Scientists don’t know why the left side seemed to be affected more, but they suspect the compounds interfere with an early biochemical process that helps the fetal brain divide into slightly asymmetrical hemispheres.

The damage, however, is not isolated to prenatal stages, or to the left hemisphere. Postnatal PAH exposure, measured at age 5, correlated with diminished white matter in areas of the prefrontal cortex of both hemispheres, the study found.

“It’s a double hit,” Peterson said. “They have the abnormality from prenatal life throughout the left hemisphere and then on top of that they have this bilateral frontal hit from exposures around age 5.”

The 40 children were from nonsmoking homes and had little or no exposure to lead or insecticides that likewise have been linked to developmental and behavioral problems, according to the study. All were right-handed.

Although it remains possible that other pollutants could be affecting the results, the researchers said their sampling methods eliminated the major contenders, helping to isolate the effects of the PAH compounds.

Numerous studies have linked air pollution — especially particulate matter — to respiratory and cardiac problems. But over the last decade, researchers have accumulated more evidence that particles and other types of airborne pollution can affect brain development.

A 2012 study using a database of 19,000 nurses found greater cognitive decline among older women exposed to high levels of particulate matter.

A 2011 Boston study involving 680 men showed similar results. A series of studies involving children in Mexico City linked air pollution with the brain inflammation that is typical of diseases such as multiple sclerosis.

“It is worrisome,” Peterson said of the latest findings. “California has gone a long way toward improving and cleaning up the air, but there’s a long way to go. Future generations depend on it.”

Source: LA Times

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Video: Presentation on air pollution and pre-term birth

Dr. Amy Padula of Stanford University discusses how women who are exposed to traffic-related air pollution during pregnancy tend to have pre-term birth babies, especially for those exposed in the second trimester.  

 

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Scientists: Early exposure to traffic pollution may be the cause of childhood #asthma

Photo: freedigitallphotos.net

A research team led by scientists at the University of California, San Francisco has found that exposure in infancy to nitrogen dioxide (NO2), a component of motor vehicle air pollution, is strongly linked with later development of childhood asthma among African Americans and Latinos.

The researchers said their findings indicate that air pollution might, in fact, be a cause of the disease, and they called for a tightening of U.S government standards for annual exposure to NO2.

The study is reported online currently in the American Journal of Respiratory and Critical Care Medicine ahead of print publication.

In the study, the largest to date of air pollution exposure and asthma risk in minority children in the United States, the team found that for every five parts per billion increase in NO2 exposure during the first year of life, there was a 17 percent increase in the risk of developing asthma later in life.

The study involved 3,343 Latino and 977 African American participants.

"Many previous studies have shown an obvious link between traffic-related pollution and childhood asthma, but this has never been thoroughly looked at before in an all-minority population," said lead author Katherine K. Nishimura, MPH, a graduate student in the laboratory of senior author Esteban G. Burchard, MD, MPH, a UCSF professor of bioengineering and therapeutic sciences and medicine and director of the UCSF Center for Genes, Environment & Health.

Minorities tend to live in areas of higher air pollution and have a higher risk of developing asthma, the researchers said.

What made the current study different from previous research, said Nishimura, was that the scientists looked retrospectively at the study participants' exposure to air pollution in early childhood, before they developed asthma. Children who developed asthma before this exposure period were excluded.

"Any participant with asthma in this study was exposed to air pollution in infancy, before they developed the disease, which is a step in the right direction in inferring causality," said Nishimura.

"This work adds to the growing body of evidence that traffic-related pollutants may be causally related to childhood asthma," said Burchard.

Study co-author John R. Balmes, MD, of UC San Francisco and UC Berkeley, pointed out that a previous study of children living in southern California showed that living and attending school close to major roadways was associated with an increased risk of new-onset asthma. "Together with our findings, this makes for strong evidence that reducing children's exposure to traffic emissions can prevent some cases of asthma," said Balmes.

One immediate implication of the study, said Burchard, is that the national standard for NO2 set by the Environmental Protection Agency (EPA) is "too lax by far." He noted that the current EPA annual standard is 53 parts per billion (ppb), while the study subjects were exposed, on average, to 19 ppb during the first year of life.

"Children growing up in southern California have been shown to have reduced growth of lung function when annual NO2 levels exceed the current national annual standard," added Balmes.

The participants, who were 8 to 21 years old and had no other lung diseases or chronic illnesses, were recruited from study centers in Chicago, New York City, Houston, the San Francisco Bay Area, and Puerto Rico. To adjust for instances when study participants moved residences, air pollution exposure for all subjects was assessed by using the residential histories from birth through time of recruitment. The researchers based their air pollution exposure estimates on EPA annual measurements.

"The geographic diversity of the study population strengthens the results, because the effects we see are consistent across a wide range of urban environments and conditions," said Nishimura. While the study was not designed to investigate how air pollution might cause childhood asthma, said Nishimura, the investigators are looking at two possible causes.

The first is that NO2 can interact with a number of other pollutants to create reactive oxygen species — chemically reactive molecules containing oxygen — which can, in turn, damage developing lungs. Immune systems that develop under such conditions, she said, could be "trained" to respond to pollutants as triggers that could later induce asthma.

Another possible explanation, said Nishimura, is that pollutants can potentially cause a genetic predisposition to asthma by altering methylation patterns in DNA. Methylation is a chemical change that alters gene expression without affecting the underlying structure of the DNA itself.

"It has been shown that changes in methylation, which can be affected by pollution, tobacco smoke and even stress, can be inherited across multiple generations," said Burchard. "Our group is currently investigating methylation as the possible outcome of exposures to a number of pollutants."

Burchard cautioned that air pollution is "not the entire story," noting that despite its low air pollution levels, Puerto Rico has the highest asthma prevalence and morbidity in the United States. "This is intriguing, and leaves us more work to do," he said.

Prenatal exposure to traffic is associated with respiratory infection in young children

Living near a major roadway during the prenatal period is associated with an increased risk of respiratory infection developing in children by the age of 3, according to a new study from researchers in Boston.

"The connection between in utero and early life cigarette smoke exposure and adverse infant respiratory outcomes is well-established, but the relation of prenatal ambient air pollution to risk of infant respiratory infection is less well-studied," said lead author Mary Rice, MD, a pulmonary and critical care fellow at Massachusetts General Hospital and Beth Israel Deaconess Medical Center. "Our study extends previous findings by showing that proximity to a major roadway during the prenatal period is associated with increased risk of subsequent respiratory infection in children."

The study included 1,271 mother-child pairs enrolled during the first trimester of pregnancy between 1999 and 2002 in Project Viva in eastern Massachusetts. The distance from home addresses to the nearest Federal class 1/2A ("major") roadway was calculated using geographic information system software. Respiratory infections were defined as maternal report of any doctor-diagnosed pneumonia, bronchiolitis, croup or other respiratory infection from birth until age 3.

Statistical analyses of the relationship between exposure to a major roadway and respiratory infection were adjusted for gender, birth weight, maternal education, household income, neighborhood income and education, maternal smoking during pregnancy, postnatal household smoking, breastfeeding, daycare attendance, presence of other young children in the household and season of birth.

Of the 1,271 mother-child pairs studied, 6.4% lived less than 100 meters, 6.5% lived 100 to 200 meters, 33.7% lived 200 to less than 1000 meters and 53.4% lived 1,000 meters or more from a major roadway.

By the age of 3, 678 (53.3%) of the children had had at least one doctor-diagnosed respiratory infection. After adjustment for possible confounders and risk factors for respiratory infection, children whose mothers lived less than 100 meters from a major roadway during pregnancy were 1.74 times as likely as those living 100 meters or more from a major roadway to have had a respiratory infection. Those living 100 to 200 meters from a major roadway were1.49 times as likely to have had a respiratory infection.

"In our study, living in close proximity to a major roadway during pregnancy was associated with an increased risk of respiratory infection in children, adding to the growing body of evidence linking exposure to traffic with adverse effects on health," said Dr. Rice. "Future research will need to clarify whether the apparent harmful postnatal effects of living close to a major road during pregnancy is due to air pollution from traffic or other exposures related to roads. We plan to further explore this connection using a measure of black carbon, a component of traffic-related air pollution. Using black carbon measures, we also plan to disentangle the associations of pre- vs postnatal air pollution exposures with respiratory infection in early life."