FRIDAY, Aug. 4, 2017 (HealthDay News) -- Exposure to certain flame-retardant chemicals in pregnancy may be linked to lower intelligence in children, a new research review suggests.
The synthetic chemicals are known as polybrominated diphenyl ethers or PBDEs. Although phased out in manufacturing in the United States, they remain in many products, including old couches and other household items, building materials and electronics, the researchers said.
Together, the studies reviewed suggested that IQs dip by 3.7 points for every 10-fold increase in prenatal exposure to these flame retardants.
"Even the loss of a few IQ points on a population-wide level means more children who need early interventions, and families who may face personal and economic burdens for the rest of their lives," said study co-author Tracey Woodruff.
Although the findings don't show a direct cause-and-effect relationship, they "go beyond merely showing a strong correlation," Woodruff said, noting her team "considered factors like strength and consistency of the evidence."
PBDEs became widespread four decades ago to disrupt combustion and spread of fire in furniture, clothing and electrical devices. The problem is, they can leach out from products, according to the U.S. Environmental Protection Agency.
Despite some bans and phase-outs, "everyone is exposed to PBDEs, so this means that there are potentially millions of IQ points that are lost across the population," said Woodruff, a professor with the University of California, San Francisco.
What's more, "children can be affected for generations to come," she added.
Over the past 40 years, prevalence of neurodevelopmental disorders -- such as autism and attention-deficit/hyperactivity disorder (ADHD) -- has increased, the study authors said in background notes. Genetics, improved diagnostics, or known environmental risk factors can't completely explain the uptick, they noted.
The researchers included 15 studies in the review covering nearly 3,000 mother-child pairs in all. Four looked at links between exposure to the chemicals and IQ levels in children. One of these examined women who were pregnant on Sept. 11, 2001, in New York City, the day the Twin Towers were attacked.
Study co-author Dr. Bruce Lanphear, a professor at Simon Fraser University in British Columbia, Canada, described the IQ effect this way: "A subtle downward shift in IQ in a population of children can have a substantial shift on the number of children who fall below an IQ of 70 points, which is considered challenged."
Moreover, children are simultaneously exposed to a "whole host of toxic chemicals that diminish intellectual ability, like lead, mercury, air pollutants, pesticides and PBDEs," he added.
"Some children will be exposed to sufficiently high levels of several chemicals, and the cumulative impact -- especially among impoverished communities where these exposures are often concentrated -- can be substantial," Lanphear said.
The researchers also looked at studies examining possible links between the chemicals and ADHD, and found what they described as moderate-quality evidence of a "limited" effect.
Bryan Goodman, speaking for the American Chemistry Council's North American Flame Retardant Alliance, said the chemicals were voluntarily phased out of production years ago.
Major manufacturers of flame retardants "have spent millions of dollars on research both before and after their products go on the market," Goodman said. Also, he pointed out, flame retardants are subject to review by regulators.
The findings were published Aug. 3 in Environmental Health Perspectives.
For more on concerns about PBDEs, see the U.S. Environmental Protection Agency.