According to a study to be published next month in Environmental Health Perspectives, circulating levels of mercury are not elevated in children with autism compared to typically developing children. This study is particularly important, as parent advocacy and practitioner groups have focused on mercury toxicity and mercury chelation treatments as key interventions in the biological treatment of this common condition.
Blood mercury levels in both autistic children and typically developing controls were similar those found in previous population samples in the age group, and on average were far below levels toxicologists consider dangerous.
Perhaps predictably, these advocacy groups have suggested that methodological problems make this research less than meaningful. As the study critics have pointed out, there is no perfect screening test for mercury exposure, limiting the level of proof demonstrated by this type of study. Still, the emerging scientific picture is not fully consistent with mercury as a major causative agent.
One aspect of this EHP study that will probably be lost in the concerns about validity of the screening test is that finding that mercury levels are best correlated with fish intake. While advocates have largely focused on mercury exposure from vaccines, a single serving of canned tuna on average contains as much or more mercury as found in thimerosal-containing vaccines. Dental amalgam was also positively associated with mercury exposure in a subset of the children who either regularly chewed gum or showed teeth-grinding behavior.
The study author, interviewed by Reuters, indicated that this study suggests that autism is likely to be caused by a number of different factors rather than a single catastrophic environmental exposure. I’d argue that this study showed no such thing, just a lack of strong association with circulating levels of mercury. Otherwise, I think we continue to need to be open to any new potential explanations that surface.
Which brings me to my central beef with the mercury / autism hypothesis… The certainty I hear these patient advocacy groups express not only defies reason, but it also acts to shut down inquiry into new and potentially fruitful directions.