By Kathryn Doyle

(Reuters Health) - Children whose mothers were exposed to higher levels of phthalates, common chemicals in consumer products, in late pregnancy tend to score lower than other kids on intelligence tests at age seven, according to a new study.


Some soaps, nail polish, hairspray, shower curtains, raincoats, car interiors and dryer sheets contain phthalates, which are used as so-called plasticizers, or softening agents.


At present, the Food and Drug Administration does not have evidence that phthalates as used in cosmetics pose a safety risk, but six types of phthalates are currently banned from children’s toys, according to the U.S. Consumer Product Safety Commission.


There are no regulations on a pregnant woman’s exposure to the chemicals, and phthalates are usually not labeled on products in the U.S.


“This is the only study looking at this in a longitudinal fashion,” said lead author Pam Factor-Litvak, a professor at Columbia University’s Mailman School of Public Health in New York, noting that this study only observed a relationship and did not test cause and effect.


“I think that there would need to be more studies to build up causation,” Factor-Litvak said.


Researchers followed 328 New York women in low-income communities from pregnancy until the child was seven years old.


During late pregnancy, researchers tested the women’s urine for di-n-butyl phthalate (DnBP), di-isobutyl phthalate (DiBP), di-2-ethylhexyl phthalate and diethyl phthalate.


When the children were seven, they completed an intelligence test measuring four areas of mental functioning.


The mothers’ levels of two of the phthalates - DnBP and DiBP - during pregnancy were associated with childhood intelligence: As phthalate levels went up, child IQ tended to go down.


When the researchers divided the mothers into four groups based on the amount of phthalates in their urine, kids whose mothers had the highest levels had an intelligence quotient (IQ) score about seven points lower than kids whose mothers had the lowest levels of the chemicals in their urine, according to the results in PLOS ONE.


The difference persisted when the authors accounted for other factors that can influence IQ, including the mother’s IQ, her alcohol use during pregnancy, education, marital status and the child’s birth weight.


“With observational studies, there is always the chance that the results may be in part explained by an unmeasured factor that we haven’t yet considered,” said Stephanie Engel, associate professor of epidemiology at UNC Gillings School of Global Public Health in Chapel Hill, North Carolina.


“I would characterize this study as thorough and high quality, and the results concerning,” said Engel, who was not involved in the work. “But there needs to be more research in this area before firm conclusions can be drawn.”


Nevertheless, on a population level, six IQ points is a very significant shift, she told Reuters Health.


“It is clear that there needs to be a serious discussion in the scientific and policy communities about whether the evidence is strong enough yet to warrant widespread policy changes, not just on the basis of this study, but also including a range of childhood health outcomes that have already been reported in the literature,” Engel said.


Phthalates and similar chemicals, including bisphenol A (BPA), have also been associated with childhood obesity and asthma.


Factor-Litvak and her coauthors previously looked at the possible effects on motor skills in three-year-old children, and the results were similar.


Although there are no regulations on phthalate exposure during pregnancy, it would be prudent for expectant mothers to avoid microwaving food in plastic, avoid scented products, avoid plastics labeled #3, #6 or #7, and as much as possible store foods in glass instead of plastic, she said.


It might be prudent for everyone, not just pregnant women, to take note of these chemicals, she said.


“Because they are so ubiquitous it’s very hard to avoid right now but you can reduce your use of those products as much as possible,” she told Reuters Health.


Based on animal studies, researchers have several theories about how phthalates might affect development, including disrupting sex hormones, thyroid hormones or dopamine-sensitive activity in the brain, she said.


SOURCE: PLOS ONE, online December 10, 2014.