Autistic children and blood mercury levels

By Grant Jacobs 27/10/2009

Autism has received great attention over the past couple of decades, from movies like Rain Man to the fuss stirred up by anti-vaccine promoters who insist that “mercury” (thimerosal) in vaccines causes autism.

If you’ve ridden the waves of the autism-related anti-vaccine silliness on the WWW you’ll appreciate research that tries bring back a positive focus on what causes autism. Of course, part of that is trying to convince those promoting the notion that mercury causes autism to (please) stop.

For these people it has never been “about” autism, really, but about the anti-vaccine movement hijacking public interest in autism to their cause. Their interest is with having an excuse to justify their anti-vaccine stance. History shows that once this reason is removed, they’ll just go on to find another excuse to justify their stance.

Taking a pre-conceived stance in the absence of evidence then insisting that it “must” be the case is a fallacy. (It’s the same fallacy I recently saw in a chiropractor’s argument that the serious ill swine flu patients “must” have an “underlying health condition” despite no evidence that they did.)

Recently another research study weighed in against thimerosal in vaccines having a role in autism (references 1 & 2), surveying 452 children aged 2-5.

The nice thing about this study is that it positively affirms what is associated with higher mercury levels in the blood, and it’s not autism or vaccines. It’s mostly eating fish.

In order of largest to smallest correlation, the factors tested that correlated with higher mercury levels were eating fish and to a lesser extent dental amalgam (the silver-coloured material used in dental fillings) in children who ground their teeth and/or chewed gum. This is consistent with previous observations that fish and dental amalgam are good predictors of blood mercury levels. Ear wax removers or nasal sprays were also associated, but not at a significant level overall.

Different types of fish were found to affect mercury levels, in order: ocean fish, tuna fish, fresh water fish (highest level of mercury to lowest). The amount of mercury related to the amount of fish eaten, the more eaten, the higher the level of mercury. The association of ocean fish, in particular tuna, with high mercury levels is well-known and ascribed to these fish slowly accumulating the mercury from the smaller fish they prey on.

Taking a thimerosal-containing vaccine prior to testing was not associated with higher mercury levels. (Thimerosal is the compound in vaccines containing bound mercury that the anti-vaccine lobby protest about. Most vaccines that previously had thimerosal no longer do to reduce the impact of the hype.)

Autistic or developmentally-delayed children in the study had slightly lower levels of blood mercury than normal children. It was suspected this was a consequence of eating less fish.

Accounting for the factors that correlated with higher mercury levels revealed that the levels of mercury in children with autism was about the same as for non-autistic children once the other factors were considered.

This study adds more weight to the now many studies showing that thimerosal in vaccines makes no contribution to autism, but it cannot rule out mercury having a role in autism at a much younger age.

Assuming autism has prenatal origins or starts in very young infants, a formal test of if mercury has a role in autism, or not, would require testing pre-natal or very young infants; the children tested in this study were 2-5 years old.

However, this study does indicate that mercury is an unlikely suspect.

The results indicate that the “mercury environment” of these children and their families are essentially the same as for families of non-autistic children.

It shows that it is unlikely that autistic children have a weakened metabolism of mercury, which some (anti-vaccine) people propose allows mercury to accumulate in their bodies. If this were true, there would be higher levels of mercury in the autistic children, but this was not observed.

I’ve now seen more than enough research trying to resolve the notion that thimerosal vaccines are associated with autism. While formally there is more to do to clear this issue completely, I prefer to focus on determining just what does cause autism and in my next post on this topic, I’ll do just that.

References (all open access)

1. CHARGE Study Shows Comparable Blood Mercury Levels in Children with Autism and Typical Development (Press release of Environmental Health Perspectives).

2. Blood Mercury Concentrations in CHARGE Study Children with and without Autism

Hertz-Picciotto et al., Environmental Health Perspectives on-line in advance, in press (2009)

3. If you want a extensive round-up of papers and blog articles explaining
the, try Vaccines and Autism at Science-Based Medicine blog.
Hertz-Picciotto I, Green PG, Delwiche L, Hansen R, Walker C, & Pessah IN (2010). Blood Mercury Concentrations in CHARGE Study Children with and without Autism. Environmental health perspectives, 118 (1), 161-6 PMID: 20056569

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