Mercury Can Make You Smart!

One of the readers of this blog, a pediatrician from Los Angeles, sent me a review of CDC study on vaccines. The study, which appeared in the New England Journal of Medicine in 2007 (357: 1281-1292), is reviewed in The Vaccine Quarterly (2:1, p. 7) by J. M. Lieberman, MD.

Here are a few excerpts from the review:

Thimerosal is a mercury-containing preservative that has been used in vaccines and some immune globulin products since the 1930s. Some people believe that infants exposed to thimerosal are at risk for neurodevelopmental problems, most notably autism, during childhood.

[Here's where it gets interesting]:

. . . higher prenatal mercury exposure was associated with better performance on one measure of language and poorer performance on one measure of attention and executive functioning. Increasingly levels of mercury exposure from birth to 7 months were associated with better performance on one measure of fine motor coordination and on one measure of attention and executive functioning. Increasing mercury exposure from birth to 28 days was associated with poor performance on one measure of speech articulation and better performance on one measure of fine motor coordination.

[Thus]:

The results do not support a casual association between early exposure to mercury from thimerosal-containing vaccines and immune globulins and deficits in neuropyschological functionaing at 7 to 10 years of age.

[All in all]:

there were a total of 19 significant effects associated with thimerosal expsoure - 12 improved outcomes, 7 poorer outcomes. Altogether, the study employed 378 statistical tests. Therefore, the statistically significant outcomes represented approximately 5% of total outcomes, suggesting that the "significant" outcomes were significant by chance alone, not by true casuality.

Lieberman argues that this idea of an "epidemic" stems "in large part" from "broadened case defintions and better case ascertainment, not a true increase in incident disease." In others words, the criteria for what defines the illness is larger, and the medical community is getting better at discovering illness. These two factors, ascendent, happen to coincide with the so-called "explosion" of cases of autism that are thought to have directly come about from exposure to thimerosal.

Lieberman ends his review with the following thought:

Science usually doesn't sway "true believers," and in this case we seem tobe dealing with a belief in a serach of validation--the hypothesis has been rejected. The most convincing evidence will come when the removal of thimerosal from vaccines does not lead to a fall in the rates of autism; this has already been demonstrated in other countries.

We will soon hear claims that if it is not thimerosal in vaccines that has harmed our children, it must be something else. Are you ready for the aluminum controversy?