COLUMBIA UNIVERSITY
Children exposed during pregnancy to elevated levels of two
common chemicals found in the home—di-n-butyl phthalate (DnBP) and di-isobutyl
phthalate (DiBP)—had an IQ score, on average, more than six points lower than
children exposed at lower levels, according to researchers at Columbia
University’s Mailman School of Public Health.
The study is the first to report a link between prenatal
exposure to phthalates and IQ in school-age children. Results appear online in
the journal PLOS
ONE. DnBP
and DiBP are found in a wide variety of consumer products, from dryer sheets to
vinyl fabrics to personal care products like lipstick, hairspray, and nail
polish, even some soaps. Since 2009, several phthalates have been banned from
children’s toys and other childcare articles in the United States. However, no
steps have been taken to protect the developing fetus by alerting pregnant
women to potential exposures. In the U.S., phthalates are rarely listed as
ingredients on products in which they are used.
Researchers
followed 328 New York City women and their children from low-income
communities. They assessed the women’s exposure to four phthalates—DnBP, DiBP,
di-2-ethylhexyl phthalate, and diethyl phthalate—in the third trimester of
pregnancy by measuring levels of the chemicals’ metabolites in urine. Children
were given IQ tests at age 7.
Children
of mothers exposed during pregnancy to the highest 25 percent of concentrations
of DnBP and DiBP had IQs 6.6 and 7.6 points lower, respectively, than children
of mothers exposed to the lowest 25 percent of concentrations after controlling
for factors like maternal IQ, maternal education, and quality of the home
environment that are known to influence child IQ scores. The association was
also seen for specific aspects of IQ, such as perceptual reasoning, working
memory, and processing speed. The researchers found no associations between the
other two phthalates and child IQ.
The
range of phthalate metabolite exposures measured in the mothers was not
unusual: it was within what the Centers for Disease Control and Prevention
observed in a national sample.
“Pregnant
women across the United States are exposed to phthalates almost daily, many at
levels similar to those that we found were associated with substantial
reductions in the IQ of children,” says lead author Pam Factor-Litvak,
PhD, associate professor of Epidemiology at the Mailman School.
“The
magnitude of these IQ differences is troubling,” says senior author Robin Whyatt,
DrPH, Professor of Environmental Health Sciences and deputy director of the
Columbia Center for Children’s Environmental Health at the Mailman School. “A
six- or seven-point decline in IQ may have substantial consequences for
academic achievement and occupational potential.”
“While
there has been some regulation to ban phthalates from toys of young children,”
adds Dr. Factor-Litvak, “there is no legislation governing exposure during
pregnancy, which is likely the most sensitive period for brain
development.
Indeed, phthalates are not required to be on product
labeling.”
While
avoiding all phthalates in the United States is for now impossible, the
researchers recommend that pregnant women take steps to limit exposure by not
microwaving food in plastics, avoiding scented products as much as possible,
including air fresheners, and dryer sheets, and not using recyclable plastics
labeled as 3, 6, or 7.
The
findings build on earlier, similar observations by the researchers ofassociations
between prenatal exposure to DnBP and DiBP and children’s cognitive and motor
development and behavior at age 3. This September, they reported a link between prenatal
exposure to phthalates and risk for childhood asthma.
It’s
not known how phthalates affect child health. However, numerous studies show
that they disrupt the actions of hormones, including testosterone and thyroid
hormone. Inflammation and oxidative stress may also play a role.
The
research was supported by grants from the National Institute of Environmental
Health Sciences (NIEHS) (R01ES013543, R01ES014393, R01ES08977) and by a
NIEHS/U.S. Environmental Protection Agency grant (P50 ES09600/RD 83214101).
Additional
co-authors include Antonia M. Calafat at the Centers for Disease Control and
Prevention in Atlanta; and Beverly Insel, Xinhua Liu, Frederica Perera, and
Virginia Rauh—all at the Mailman School.
