In yet another study on mercury and autism, a team from the University of Texas has investigated blood mercury levels in children with autism spectrum disorders (ASDs). In Seafood Consumption and Blood Mercury Concentrations in Jamaican Children With and Without Autism Spectrum Disorders they report that “After controlling for the child’s frequency of seafood consumption, maternal age, and parental education, we did not find a significant difference (P = 0.61) between blood mercury concentrations and ASDs. ”
“we did not find a significant difference between blood mercury concentrations and ASDs”
Here is the abstract:
Mercury is a toxic metal shown to have harmful effects on human health. Several studies have reported high blood mercury concentrations as a risk factor for autism spectrum disorders (ASDs), while other studies have reported no such association. The goal of this study was to investigate the association between blood mercury concentrations in children and ASDs. Moreover, we investigated the role of seafood consumption in relation to blood mercury concentrations in Jamaican children. Based on data for 65 sex- and age-matched pairs (2-8 years), we used a General Linear Model to test whether there is an association between blood mercury concentrations and ASDs. After controlling for the child’s frequency of seafood consumption, maternal age, and parental education, we did not find a significant difference (P = 0.61) between blood mercury concentrations and ASDs. However, in both cases and control groups, children who ate certain types of seafood (i.e., salt water fish, sardine, or mackerel fish) had significantly higher (all P < 0.05) geometric means blood mercury concentration which were about 3.5 times that of children living in the US or Canada. Our findings also indicate that Jamaican children with parents who both had education up to high school are at a higher risk of exposure to mercury compared to children with at least one parent who had education beyond high school. Based on our findings, we recommend additional education to Jamaican parents regarding potential hazards of elevated blood mercury concentrations, and its association with seafood consumption and type of seafood.
Members of this team have other work on autism in Jamaica. Last year they presented Paternal and Maternal Age Are Jointly Related to Autism Spectrum Disorders In Jamaican Children at IMFAR. which had goals of:
This study’s primary objectives were to investigate whether environmental exposures to mercury, lead, arsenic and cadmium play a role in autism. Additionally, we investigated other potential risk factors for autism, including maternal and paternal age
So we see that the recently released paper is part of the conclusion of that study, which was incomplete at the time of abstract submission for IMFAR. I believe this team is reporting again at IMFAR 2012.
Why bring this up? It’s a relatively small study on a topic that has been well covered in the past: autism risk and mercury exposure. Besides, do even supporters of the autism/mercury hypothesis think that blood levels of mercury are a good indicator to track? The answer is “yes” when blood levels might implicate mercury and “no” when blood levels do not (as is this case).
The mercury/autism hypothesis has a long history, but it is worth noting that there was a great deal of excitement a few years ago when a researcher claimed that by re-analyzing an existing dataset she could show a correlation between blood mercury levels and autism. Porf. DeSoto’s 2007 paper was Blood Levels of Mercury Are Related to Diagnosis of Autism: A Reanalysis of an Important Data Set . The re-analysis was criticized (e.g. Autism Street’s A Tale Of Two Tails and A Photon in the Darkness’ Winter Potpourri ). As noted, the re-analysis was also welcomed in some circles, including an article by Age of Autism’s Mark Blaxill: :
This is an important and unexpected finding. It supports one of the central hypotheses at the heart of the autism-mercury controversy and suggests that the excretion deficit in autistic children might persist longer than anyone had guessed.
The idea that correlations between blood levels in autistics could be “an important…finding” was downplayed a great deal a few years later after Prof. Hertz-Picciotto’s team at the U.C. Davis MIND Institute came out with a study, Blood mercury concentrations in CHARGE Study children with and without autism . The MIND team concluded, “After accounting for dietary and other differences in Hg exposures, total Hg in blood was neither elevated nor reduced in CHARGE Study preschoolers with AU/ASD compared with unaffected controls, and resembled those of nationally representative samples”. Key in that conclusion—”after accounting for dietary and other differences in Hg exposures”. This is something that was not done in the dataset that Prof. DeSoto re-analyzed.
Which led to a press release from Mr. Blaxill’s organization, SafeMinds: which downplayed any impact of the MIND study while somewhat ironically using DeSoto’s re-analysis for support. In other words, new research on blood-levels of mercury are not so important because we have older, uncontrolled, data which does say blood-levels are important.
More telling of the shift in support for blood mercury concentrations is this 2010 comment from:
Measuring random blood levels is a fruitless exercise, like testing ASD kids for grass allergies in the wintertime.
Don’t assume the door was closed on blood levels of mercury. In 2011 a paper was published, Theoretical aspects of autism: Causes—A review , which stated that there was evidence for a “metal metabolism disorder” in autistics and Supporting this relationship are reports documenting that heavy metals are increased in the blood and urine of autistic subjects”. This review was not surprisingly promoting the idea that vaccines and/or mercury cause autism as well as criticized by many ( for example )
So while, yes, these groups do welcome research indicating that blood levels of mercury are important in discussing autism research, they are also quite prepared to downplay using on blood-levels of mercury in studies which don’t support the mercury-causation idea.
Which is why one will not be surprised that research such as this new paper from Jamaica will have little impact on the mercury-causes-autism movement. Well, that and the fact that it is evidence against causation.
For those who claim that mercury testing should be done earlier—that testing autistic children is too late (“like testing ASD kids for grass allergies in the wintertime”) there is another study in process, one that was presented at IMFAR 2011. Prenatal and Neonatal Peripheral Blood Mercury Levels and Autism Spectrum Disorders which I don’t believe has been published yet. The conclusion from that study: “Levels of total mercury in serum collected from mothers during mid-pregnancy and in blood collected from infants at birth were not associated with risk of ASD.”
Mercury levels in pregnant women aren’t correlated to whether their children have autism. Mercury levels in newborns aren’t associated with autism risk. Blood levels in autistics are not correlated with their diagnosis. Add to this the fact that autism risk is not correlated to levels of mercury exposure from vaccines or immunoglobulins (e.g. Prenatal and Infant Exposure to Thimerosal From Vaccines and Immunoglobulins and Risk of Autism ). And the fact that autism does not look like mercury intoxication . And that autism prevalence estimates continue to rise even after mercury was removed from vaccines. Why is there still support for this idea?