Prenatal exposure to common chemicals linked to lower IQ

A pregnant woman holds the bottom of her belly. (Twonix Studio / shutterstock.com)

A new study is drawing a link between two common plastics chemicals and low IQ scores among kids exposed to the chemicals in their mothers' wombs.

The study, from researchers at Columbia University's Mailman School of Public Health, found that children exposed during pregnancy to high levels of the two phthalate chemicals were, on average, six or more points lower than children exposed to lower levels.

The study focused on two chemicals -- di-n-butyl phthalate (DnBP) and di-isobutyl phthalate (DiBP) -- which are found in several household products. The chemicals help make plastics soft, and are used in vinyl products such as shower curtains, dryer sheets and personal care products such as hairspray and nail polish.

For the study, researchers looked at 328 New York City women and their children. They assessed the women's exposure to four phthalates in the third trimester of pregnancy by measuring levels of the chemicals in their urine. Then, the children were given IQ tests at age 7.

The children of mothers exposed to the highest 25 per cent of concentrations of DnBP and DiBP had IQs 6.6 and 7.6 points lower than children of mothers exposed to the lowest 25 per cent of concentrations. The researchers said they controlled for other factors that could affect the children's IQ, such as the mother's IQ, her education, and quality of the home environment.

The researchers found no links between two other phthalates and child IQ.

The full results appear in the journal PLOS ONE.

The study was not able to conclude that the chemical exposure was the cause of the lower IQ scores in the children.

Still, senior author Robin Whyatt, a professor of Environmental Health Sciences, says the magnitude of the IQ differences was troubling.

"A six- or seven-point decline in IQ may have substantial consequences for academic achievement and occupational potential," he said in a statement.

The authors say pregnant women are exposed to phthalates almost daily, many at levels similar to those they found in their study were linked to lower IQ.

They say most products containing these phthalates do not list them as ingredients and there are no laws requiring such labelling.

While some phthalates have been banned from toys, avoiding all phthalates is impossible, the researchers say.

They offer the following recommendations to pregnant women to help them reduce their exposure: