The Mercury-Autism Link IV
Bill Long 8/27/08
1999-2000 NHANES Study
When the Bernard et al. article came out in 2001, it argued that autism was primarily a form of mercury poisoning. In the next few years the "hair studies" began--in which scientists tried to measure the amount of mercury in first-cut baby hair (from baby books) of autistic children and "controls." They wanted to use this method as a way of confirming or disconfirming the thesis advanced in the Bernard paper. The theory behind the research is that if the autistic children showed a much lower rate of mercury concentration in hair samples, then the chances are good that they have had trouble excreting mercury, that mercury still resides in their system, and that the mercury in their system may have "caused" the autism. If it can be shown that autistic children also carry a mercury burden exceeding that of neurotypical children, one might have laid the basis for chelation treatment--which is a long-recognized practice for removing heavy metals (mercury included) from the body.
Shortly after the Bernard paper came out, a summary paper published by NHANES (National Health and Nutrition Examination Survey) entitled "Hair Mercury Levels in US Children and Women of Childbearing Age: Reference Range Data from NHANES 1999-2000" appeared. The study didn't look at mercury levels in autistic children, but it did establish some "base lines" for mercury levels, gathered through hair samples, of 1,726 pregnant women (ages 16-49) and 838 children (ages 1-5) in the USA. Hair sampling, the study said, was the "preferred biomarker" for determining mercury levels in people. This study only asked study participants regarding level of fish consumption (fish contribute to the level of methylmercury in a human); it didn't look at vaccines or antibody use or dental amalgams. The results were these:
"Among children, the overall GM (i.e., geometric mean) total hair Hg was 0.12 mg/g (micrograms per gram). Non-Hispanic black and Mexican-American children had higher Hg levels than non-Hispanic white children. Boys had higher (nonsignificant) hair Hg levels than girls in all race/ethnicity groups. For women, non-Hispanic white females had significantly higher GM hair Hg levels than did non-Hispanic blacks and Mexican Americans."
Since they were trying to correlate mercury levels with fish consumption, the study also had conclusions about this:
"GM hair Hg increased with increasing frequency of fish consumption for children and adults. The GM hair Hg level of children consuming fish three or more times during the past month was twice as high as for nonconsuming children (0.16 vs. 0.08 mg/g). Frequent fish consumers 30-49 years of age had the highest GM hair Hg levels of the adult groups examined (0.41 mc/g)."
The paper goes on to say that "the total Hg levels of NHANES children and women were generally lower than the levels reported in other studies of US and international populations." For example, the GM hair level Hg in fish-consuming children seven years of age in the Faroes Islands was 2.99 mg/g comparied with a GM value of 0.16 mg/g among frequent fish consumers in the NHANES sample 1-5 years of age. Women in the Faroes Is. study had a mercury concentration of 4.5 mg/g. A Japanese study indicated lower levels of mercury in their population. Hair data for Japanese adult females residing in five districts showed an overall hair Hg GM of 1.43 mg/g, while the GM and median values for frequent fish consumers among women of childbearing age in the NHANES study were 0.77 mg/g and 0.33 mg/g respectively.
Some Conclusions and Questions
The NHANES study figures were intended to "provide a useful biomarker for long-term Hg exposure." But the authors of the linked article are aware of the limitations of the study. First, it only correlated mercury levels and fish consumption. No mention was made of other issues which are concerns to parents of autistic children. Second, it confessed that these national samples, though representative, did not permit estimation of MethylHG exposures in population groups with potentially high dietary exposures, such as subsistence fishers and residents in specific regions of the US where levels might be higher. Third, there were three "outliers" in the study, children whose levels of mercury contamination was "off the charts" and the authors didn't know exactly what to do with that... So, they were discarded (a not uncommon practice for a small number of "extreme" hair Hg values). Their conclusion ought to be emphasized:
"This underscores the complexity of Hg assessment and exposure in populations."
The most that can be said for the NHANES study is that it showed that mercury levels in hair of children and pregnant women in the US are far below those in some other fish-consuming countries. It is a "first-time" study, however, and many more are needed, especially with targeted groups, in order truly to get a national "benchmark" for mercury levels in the body.
At this point it would seem that the information is valuable but limited. Studies like this would encourage scientists and researchers sympathetic with the autism community to try to do studies that break out mercury levels in autistic vs. neurotypical children and perhaps try to identify the "culprits" more precisely that lead to higher mercury levels when they exist.
Indeed, a 2003 study by Dr. Amy Holmes, et al. in the International Journal of Toxicology (July-August, pp. 277-85), perhaps in response to the "global" data of the NHANES study, compared differential rates of mercury traces in hair of first baby haircuts of autistic and neurotypical children. The next essay speaks briefly about her study and then focuses on the 2007 testimony of Dr. Jeffrey Brant, at the Omnibus Autism Proceeding in the Cedillo case...
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