Oct 21 2009
A new study published online in Environmental Health Perspectives shows no correlation between blood mercury levels in 2-5 year old children and autism or developmental delay. This study adds to the growing evidence that environmental exposure to mercury, from any source, is not a risk factor for autism.
The study looked at 452 children aged 2-5 (which is a robust sample) with either autism spectrum disorder (ASD), other developmental delay (DD), or typically developed (TD). They found that children with ASD and DD had lower levels of blood mercury than TD controls. They further found that ASD and DD children tended to eat less fish, and as fish is by far the most significant source of mercury exposure, this explains their lower levels.
The researchers then adjusted for reported exposure to fish as well as other known sources of mercury and found that the adjusted level of mercury were the same for all groups. The levels were also similar to established national norms, meaning that the population being studied and the methods used are likely representative.
What this means is that, at least during the ages of 2-5, kids with ASD do not have higher blood levels of mercury than TD controls. It further indicates that their metabolism of mercury is not likely to be different because their adjusted levels were the same. If ASD children had a problem with eliminating mercury, as has been proposed by vaccine-autism link proponents, then we would expect that they would have a higher level of mercury for a given exposure.
The study authors are open and, I feel, fair about the strengths and weaknesses of this study. They do not have information from pre-natal and early post-natal mercury exposure or levels, so their study cannot rule out an association there.
They also do not have data on mercury levels in other tissues. Vaccine-autism link proponents claim that some children with ASD tend to store more mercury in their brains, so their higher mercury burden is not reflected in their blood levels. However, without evidence this is just special pleading. Further, there is evidence to suggest that blood levels correlate well with mercury levels in other tissues, including the brain. And further still, this study suggests that children with ASD handle mercury similarly to TD controls, as their adjusted blood levels were the same.
Of course, this one study cannot disprove a link between vaccines and autism. But this adds to the growing body of evidence for a lack of a correlation. All studies looking at exposure to thimerosal, a mercury-containing preservative in some vaccines, and autism or other neurological disorders has shown no correlation. And most significantly, when thimerosal was removed from the vaccine schedule in the US (it now remains only in some optional vaccines) there was no corresponding change in the rate of autism diagnoses. (See here for a thorough review of relevant studies.)
The utter failure of the vaccine-autism hypothesis has led some in the anti-vaccine crowd to broaden their claim to a more vague reference to “toxins” or to “environmental factors.” This study shows a lack of correlation between autism and mercury from any source.
Further, the scientific evidence is moving steadily in the direction of showing that ASD is a collection of genetic disorders, or at least has strong genetic correlates.
None of this, unfortunately, will stop the anti-vaccine movement from using the specter of ASD to scare parents away from vaccines.
17 Responses to “Another Study Showing Lack of Correlation Between Mercury and Autism”
Leave a Reply
You must be logged in to post a comment.