Another Study Debunks Mercury as Cause of Autism Spectrum Disorders

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Autism Spectrum Disorders are complex conditions with many potential causes (none yet conclusively proven), but the one possible threat studied the most heavily – mercury - has yet another study to say that there is no clear link between the two. In a study published online in PLoS One, researchers with the North Yorkshire and York Primary Care Trust find that even low-level mercury exposure is unlikely to contribute to autism.

The research team, led by Barry Wright MD, studied a diverse group of children. Fifty-four kids had been diagnosed with an autism spectrum disorder (ASD), 34 attended special schools for learning disabilities, 42 were siblings of autistic children, and 121 attending mainstream schools were studied as healthy controls.

Dr. Wright assessed levels of urinary mercury in each child which can be used to determine mercury exposure. Mercury can come from many sources, but most advocates point to Thimerosal (ethylmercury), a preservative once found in childhood vaccines. However, despite the discontinuation of this ingredient in 2001, rates of autism continue to rise.

Another potential source of mercury is dental fillings. To control for this, Dr. Wright included this factor in his assessment and noted that the number of fillings in the children with autism was slightly lower than those in other groups.

The authors note that children could also be exposed to mercury from a range of environmental sources. For example, children in Iraq in the 1970’s were exposed to mercury from a fungicide used to treat grain. Certain fish can also contain large amounts of the chemical, particularly shark, swordfish, tilefish and king mackerel.

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Mercury levels in urine did not differ between children with autism and controls, even after adjusting for factors such as urine concentration and body mass. The team also tested for other heavy metals such as lithium, manganese, and copper, but there were no difference in these components either.

Dr. Wright warns that the topic still warrants further study. He notes the study population was somewhat small, and that 24-hour urine collections may possibly have given a different result than one-time single collections, but that this task is often difficult in children with autism.

There is still so much we don’t know about autism causes. There does appear to be both genetic and environmental concerns that are linked to the disorders on the spectrum. Recently, a team at the Harvard School of Public Health found several factors that occur during pregnancy that appear to increase risk, such as low birth weight, blood type incompatibility, low Apgar score, and summer birth. Other concerns include both maternal and paternal age, medications or infections that the mother is exposed to during pregnancy, and air pollution.

The good news is, as we continue to make strides in research and in treatment options, more children will be able to live more normal lives.

Journal reference:
Wright B, et al "A comparison of urinary mercury between children with autism spectrum disorders and control children" PLoS One 2012; DOI:10.1371/journal.pone.0029547.

Photo Credit: Wikimedia Commons

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