Researchers at the Columbia Center for Children's
Environmental Health at the Mailman School of Public Health are the first to
report an association between early childhood exposure to the chemical
bisphenol A (BPA) and an elevated risk for asthma in young children. BPA is a
component of some plastics and is found in food can liners and store receipts.
Results appear in the March edition of the Journal of Allergy and Clinical Immunology.
"Asthma prevalence has increased dramatically over the
past 30 years, which suggests that some as-yet-undiscovered environmental
exposures may be implicated. Our study indicates that one such exposure may be
BPA," says lead author Kathleen Donohue, MD, an assistant professor of
Medicine at Columbia University College of Physicians and Surgeons and an
investigator at the Center for Children's Environmental Health.
How the study was
Dr. Donohue and her co-investigators followed 568 women
enrolled in the Mothers & Newborns study of environmental exposures. BPA
exposure was determined by measuring levels of a BPA metabolite in urine
samples taken during the third trimester of pregnancy and in the children at
ages 3, 5, and 7. Physicians diagnosed asthma at ages 5 to 12 based on asthma
symptoms, a pulmonary function test, and medical history. A validated
questionnaire was used to evaluate wheeze.
After adjusting for second hand smoke and other factors known
to be associated with asthma, the researchers found that post-natal exposure to
BPA was associated with increased risk of wheeze and asthma. BPA exposure
during the third trimester of pregnancy was inversely associated with risk of
wheeze at age five. This unexpected finding is in contrast to the results of a
previous study, which found that BPA exposure during the second trimester, a
critical period for the development of airways and the immune system, was
positively linked with risk for asthma.
Increased risk for wheeze and asthma was seen at
"fairly routine, low doses of exposure to BPA," says Dr. Donohue.
"Like most other scientists studying BPA, we do not see a straightforward
linear dose-response relationship."
At all three time points, more than 90% of the children in
the study had detectable levels of BPA metabolite in their bodies, a finding
that is in line with previous research. This does not mean that they will all
develop asthma, cautions Dr. Donohue. "Just as smoking increases the risk
of lung cancer but not everyone who smokes gets lung cancer, not every child
exposed to BPA will develop asthma."
The biological mechanism behind the BPA-asthma connection is
unclear. The current study found no evidence that exposure to BPA increased the
risk that the immune system would develop more antibodies to common airborne
allergens. "Other possible pathways may include changes to the innate
immune system, but this remains an open question," says Dr. Donohue.
The new study builds on existing evidence linking BPA
exposure to respiratory symptoms, as well as to obesity, impaired glucose tolerance,
and behavioural issues, among a range of health problems. In July, the Food and
Drug Administration banned BPA in baby bottles and sippy cups.
"It is very important to have solid epidemiologic
research like ours to give the regulators the best possible information on
which to base their decisions about the safety of BPA," says senior author
Robin Whyatt, DrPH, professor of Environmental Health Sciences and deputy
director of the Columbia Center for Children's Environmental Health.
To reduce exposure to BPA, the National Institute of
Environmental Health Sciences (NIEHS) recommends avoiding plastic containers
numbers 3 and 7, eating less canned food, and, when possible, choosing glass,
porcelain, or stainless steel containers, especially for hot food and liquids.