Early Exposure to Chemicals May Boost Risk of Asthma
Scientists trying to unravel why childhood asthma has reached epidemic proportions have reported that a variety of chemical exposures during infancy -- including pesticides and wood smoke -- can substantially increase a child’s risk of developing the disease.
Studying nearly 700 children in 12 communities in the Los Angeles region, a team at USC found that children exposed to household pesticides in their first year of life were more than twice as likely to develop asthma than those never exposed. Infants exposed to wood smoke, household cockroaches and farm animals also suffered considerably more asthma.
Asthma is the most prevalent disease affecting American children, causing more hospital stays and missed school days than any other chronic childhood illness. While medical officials today have a good understanding of how to treat breathing problems in asthmatics, they have struggled for years to figure out what makes so many children vulnerable to the disease.
About 20 million people in the United States suffer from asthma, including more than 3.5 million children under the age of 15. Nearly twice as many preschoolers and school-age children had asthma in 1999 than in 1980, according to a Centers for Disease Control and Prevention report. About 5,000 people die from asthma attacks in the country every year.
The USC study suggested that there was no single cause, but an array of factors in children’s lives responsible for asthma. It also indicated that contaminants -- indoors and outdoors -- have particularly potent effects on infants, so that a baby’s experiences might determine how healthy he or she is for the rest of his or her life.
“The main message is that early in life, the first year of life may be a very, very important time for respiratory health, and that children may be uniquely susceptible then,” said Dr. Frank D. Gilliland, a professor of preventive medicine at USC’s Keck School of Medicine. Gilliland was the lead author of the report, which was published in the online version of the scientific journal Environmental Health Perspectives.
The study, which was one of the largest worldwide to examine factors contributing to childhood asthma, confirmed many of the findings of other research. Of 691 children between the ages of 8 and 18 recruited for the study, 279 had asthma and 412 did not.
Eight factors included in parents’ questionnaires were compared -- day-care attendance, household pets, cockroaches, pesticides, smoke from burning wood and oil, exposure to farm animals or crops, number of siblings and breastfeeding. Only two categories -- pets and breastfeeding -- were not associated with a substantially higher risk of asthma, the report said.
In people with asthma, airways are inflamed and constricted as immune cells react to allergens, reducing the flow of air to and from the lungs and causing shortness of breath, wheezing and coughing.
Scientists have long theorized that exposure to irritants or chemicals could alter a child’s developing immune and respiratory systems.
The USC scientists said “the widespread use of pesticides and herbicides in the home and farm environments, and the magnitude of the observed risks” warrant giving priority to investigating their link to asthma.
Dr. Deepak Jajou, a pediatrician who specializes in asthma at Mount Sinai Hospital in Chicago, said asthma is an “an interplay between genetics and environment” and “that the experience of a child in early life does influence whether he develops asthma or not.”
“Clearly, wood smoke, pesticides, irritants cause problems in developing lungs. They really make things worse. Whether they cause asthma, I don’t know, but they could clearly make it come to the surface,” he said.
Jajou cautioned that the USC research and similar studies “give us some clues about causes, but they are not considered very conclusive” because they rely on parents’ subjective memories about their children’s past exposure.
Dr. Miles Weinberger, director of the Pediatric Allergy and the Pulmonary Division at University of Iowa College of Medicine, questioned the findings. He said genetics -- whether parents have asthma or allergies -- play the major role in determining which children develop asthma. Although soot, secondhand cigarette smoke and other environmental factors exacerbate symptoms and can lead to an asthma diagnosis for young children, Weinberger said he did not believe those factors caused the disease.
In the study, children exposed to smoke from burning wood or oil were 1.6 times more likely to have asthma than those never exposed.
The risk was slightly higher for those exposed during the first year of life.
Children were also twice as likely to have asthma if, as infants, they had cockroaches in their homes. Experts suspect that early exposure to the insects causes an allergic reaction. Exposure to farm animals increased the asthma rate by 60%, perhaps because of a bacteria on farms called endotoxin.
In the study, children attending day-care centers were more prone to temporary wheezing if they had colds -- especially children who attended the centers before they were 4 months old. But children at day-care centers were not more likely to develop persistent asthma than the children who did not attend day-care centers.
The chances of a child developing asthma decreased by half if he or she had four or more siblings, the study found.
Some experts suspect that children who spend a lot of time around other children develop immunity to asthma because they are exposed early and often to respiratory infections, which prompt their immune cells to be geared toward fighting bacteria.
Gilliland said the findings are not definitive because they do not examine all relevant factors, offering just “one small part of the puzzle.”
The study is part of the 10-year Children’s Health Study that has examined the effects of air pollution on about 6,000 Southern California schoolchildren.
