Nothing Fishy Here About Autism

Mercury not linked to autistic behaviors even in women with high mercury levels from fish

/ Author:  / Reviewed by: Joseph V. Madia, MD

(RxWiki News) A tuna salad sandwich can be a healthy and tasty meal. But tuna and other fish can contain small amounts of mercury. Can these amounts increase a pregnant woman's risk of having a child with autism?

Apparently not, according to a recent study.

Even among pregnant women who ate large amounts of fish that contained mercury, there was no higher risk that their children would have autism.

Pregnant women should still discuss their fish intake with their prenatal caregiver because of other risks from mercury. However, autism does not seem to be among those concerns according to this study.

"Ask your OB/GYN about your pregnancy diet."

Edwin van Wijngaarden, PhD, of the Department of Public Health Sciences at the University of Rochester School of Medicine and Dentistry in New York, and colleagues looked for possible risks for autism related to a pregnant's woman's intake of mercury.

Large carnivorous fish such as tuna and sharks can contain high amounts of mercury, and pregnant women are already advised to limit their intake of such fish.

Mercury also exists in environmental sources, from which it can get into people's bodies.

In this study, the researchers looked for whether women who ate higher amounts of fish with mercury had a higher risk of having a child with autism.

The researchers used hair samples around the time women gave birth to measure the amount of mercury exposure in 1,784 mothers who lived in the Republic of Seychelles.

The Seychelles are a chain of islands in the Indian Ocean. They were selected because residents there eat a large amount of fish.

The mothers' children were then assessed with two questionnaires to identify those with scores in the range of the autistic behaviors. The children's ages ranged from elementary through adolescent and young adult.

The average amount of mercury found in the women was 8.4 parts per million.

The average score of the children on one of the questionnaires, called the Social Communication Questionnaire, was 8 (on a scale of 0 to 28).

Only 8 percent of the children scored a 15 or higher, which indicates autistic-like behaviors.

When the researchers analyzed the mercury exposure in the mothers and their children's scores, they found no patterns showing a link between mercury and autistic-like behavior.

"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," said Dr. van Wijngaarden in a prepared statement.

"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 said.

Co-author Philip Davidson, PhD, added that women in the US already have lower levels of mercury than those found in the women in this study.

"This study shows no consistent association in children with mothers with mercury levels that were six to ten times higher than those found in the US and Europe," Dr. Davidson said in a prepared statement.

Glen Elliott, a dailyRx expert and a clinical professor at the Stanford University Department of Psychiatry and Behavioral Sciences, said this study reflects the continued search for more information about the causes of autism.

“The pressure to find a cause for autism is understandably high, as is the suspicion that at least some part of the soaring prevalence rates must be driven by a yet-to-be-uncovered change in the environment," Dr. Elliott said.

"Unfortunately, science moves slowly and has to take relatively small bites out the big range of possible environmental causes," he said. "These investigators have done a nice job of, once again, demonstrating that elevations in mercury is not the cause."

He noted that the focus on mercury in research related to autism may be outliving its usefulness.

"At some point, the field will have to conclude that we have enough negative data on this one possible toxin and move on to other possibilities," Dr. Elliott said.

This study was published July 18 in the journal Epidemiology.

The research was funded by the US National Institute of Environmental Health Sciences, National Institutes of Health and the Government of the Republic of Seychelles. The authors reported no conflicts of interest.

Reviewed by: 
Review Date: 
July 24, 2013
Last Updated:
July 26, 2013