Frank D. Gilliland, M.D., Ph.D., professor of preventive medicine at the Keck School, presented findings from the Children's Health Study at the 99th Annual International Conference of the American Thoracic Society.
Gilliland and colleagues found that exposures to cockroaches, weed killers, pesticides, fuel oil, soot, exhaust and farm crops, dust and animals beginning in the first year of life were all linked to early asthma, while babies who first attended daycare before 4 months of age also were more likely to be diagnosed with the respiratory disease later on.
"The first year of life seems uniquely important in terms of susceptibility to environmental triggers of asthma," Gilliland says.
The research team conducted the case-control study within a large subset of children participating in the ongoing Children's Health Study. Researchers with the USC-led Children's Health Study have monitored levels of major pollutants in a dozen Southern California communities since 1993, while carefully following the respiratory health of more than 3,000 students.
The researchers looked at 338 children who were diagnosed with asthma by a physician before they turned 5 years old. They then matched those children to 570 asthma-free children of the same age who lived in the same communities. They also matched them according to whether the children had been exposed to maternal smoking while still in the womb.
They found that the risk of developing asthma before age 5 rose significantly with these exposures (figures given in odds ratios):
Exposure and risk increased by:
Cockroaches in home before age 1:
Over two times (2.03)
Around herbicides before age 1:
Over four-and-a-half times (4.59)
Around pesticides before age 1:
Nearly two-and-a-half times (2.40)
Farm crops, dust or animals before age 1:
Nearly two times (1.81)
Daycare attendance before 4 months of age:
Nearly two-and-a-half times (2.34)
Wood or oil smoke, soot or exhaust anytime between birth and age 5:
More than 50 percent (1.57)
The study was not designed to find out specifically why risk increased. In general, Gilliland notes: "The first year of life is a critical time period of lung development-both for immunity and airway structure. Others have shown that certain early life exposures are important for asthma development."
In the case of daycare attendance, Gilliland theorizes that early and frequent exposure to respiratory infections, such as respiratory syncytial virus, or RSV, in a daycare setting might raise early asthma risk.
The research team found that the more older brothers and sisters a child had at birth, the lower the child's risk of early asthma. But they found nothing to indicate that other early childhood experiences such as exclusive breast-feeding or exposure to cats, dogs or other pets protect against early asthma.
More research is needed to determine what levels of exposure may be important and whether reducing exposures reduces asthma risk.
Asthma is the most common chronic disease of childhood, affecting about one in 14 children in the United States, according to the National Heart, Lung and Blood Institute, or NHLBI, one of the groups sponsoring the research. The California Air Resources Board, National Institute of Environmental Health Sciences and Environmental Protection Agency also sponsored the study.
F.D. Gilliland, M.T. Salam, Y. Li and B.M. Langholz, "Early Life Risk Factors for Asthma: Findings from the Children's Health Study," ATS 2003-International Conference of the American Thoracic Society, Mini-symposium D011, 9:15 a.m. May 21, 2003.