TUESDAY, July 23, 2013 (HealthDay News) -- Children exposed to low levels of mercury in the womb because their mothers ate large amounts of fish during pregnancy don't appear to be at increased risk for autism, a new study suggests.
Worry that low levels of mercury might affect a child's developing brain has long been a cause for concern, and some experts have suggested that the chemical element may be responsible for behavioral disorders such as autism.
The new findings from more than 30 years of research in the Republic of Seychelles -- a group of islands in the western Indian Ocean -- found no such link, the study authors said.
"This study shows no evidence of a correlation between low level mercury exposure and autism spectrum-like behaviors among children whose mothers ate, on average, up to 12 meals of fish each week during pregnancy," study lead author Edwin van Wijngaarden, associate professor in the public health sciences department at the University of Rochester Medical Center in New York, said in a medical center news release.
"These findings contribute to the growing body of literature that suggest that exposure to the chemical does not play an important role in the onset of these behaviors," he added.
One autism expert added a note of caution, however.
"The study found no link between high mercury levels and later autism spectrum disorder behaviors. However, this should not be taken to mean that high levels of mercury are safe to ingest," said Alycia Hallday, senior director of environmental and clinical science at the advocacy group Autism Speaks.
"Other studies comparing this [Seychelles] cohort to those in other parts of the world indicate that this cohort may be spared from many adverse effects because it is consumed with nutrient-rich ocean fish," she explained.
The study, published online July 23 in the journal Epidemiology, included nearly 1,800 children, teens, young adults and their mothers.
For the study, the researchers initially determined the level of prenatal mercury exposure by analyzing the mothers' hair samples. Then the researchers used two questionnaires -- one given to parents, the other to the children's teachers -- to see if the children showed signs of autism spectrum-like behaviors. The tests included questions on language skills, communication skills and repetitive behaviors. While the tests don't give a definitive diagnosis, they are used widely in the United States as an initial screening tool and may indicate the need for additional testing, the researchers said.
Eating fish during pregnancy can present a dilemma for expectant mothers and their doctors. Fish are high in a number of beneficial nutrients, including some that are essential to brain development. However, fish can contain mercury, and high levels of mercury have been shown to lead to developmental problems in children.
Although the impact of low level exposure to mercury on children remains unknown, some organizations, including the U.S. Food and Drug Administration, recommend that pregnant women limit their consumption of fish, the study authors noted.
But is that caution necessary, the study authors wonder?
"This study shows no consistent association in children with mothers with mercury levels that were six to 10 times higher than those found in the U.S. and Europe. This is a sentinel population and if (the association between low-level mercury exposure and autism) does not exist here than it probably does not exist," Philip Davidson, principal investigator of the Seychelles Child Development Study and professor emeritus in pediatrics at the University of Rochester Medical Center, said in the news release.
The finding lends support to an emerging belief that the good may outweigh the possible bad when it comes to eating fish during pregnancy. Specifically, if the mercury did not harm brain development at the levels of exposure experienced by the children in this study, then the benefits of the nutrients in fish may counteract or surpass the potential negative effects of mercury, the study authors said.
One autism expert said changes to dietary recommendations are unlikely.
"Although fish is generally viewed as an excellent dietary choice, women have been advised to limit fish consumption when pregnant," said Dr. Andrew Adesman, chief of developmental & behavioral pediatrics at Cohen Children's Medical Center of New York in New Hyde Park, NY.
Even though the study showed no mercury-autism link, "it is unlikely that dietary recommendations will be revised in light of this study alone," he said.
Funding for the study was provided, in part, by the U.S. National Institute of Environmental Health Sciences (NIEHS), part of the U.S. National Institutes of Health.
"NIEHS has been a major supporter of research looking into the human health risks associated with mercury exposure," Cindy Lawler, acting branch chief at the National Institute of Environmental Health Sciences, said in the news release. "The studies conducted in the Seychelles Islands have provided a unique opportunity to better understand the relationship between environmental factors, such as mercury, and the role they may play in the development of diseases like autism. Although more research is needed, this study does present some good news for parents."
The March of Dimes lists foods to limit or avoid during pregnancy.