You no doubt read in all the newspapers reports last week about the two articles in JAMA (click here for full text of one and here for the abstract of the other) showing that there was no need to worry about letting the dentist fill your kids’ teeth (or your own) with mercury amalgams because, well, because two large studies showed no negative effects in multiple parameters between kids who had mercury fillings and kids who had resin fillings.
It seems kind of strange to me given that mercury is an extremely toxic substance that putting large amounts of it into the body (especially the body of a child) wouldn’t cause some kinds of problems somewhere along the line. What do these papers tell us?
The first one evaluated groups of children in the New England area who had fillings done with either mercury amalgams or with a resin material containing no mercury. Researchers evaluated these two groups of children for any changes in intelligence as measured by standardized intelligence tests over a period of five years. As might be expected, the children with the mercury amalgams had greater levels of mercury in their tissues as measured by hair and urine samples.
Children assigned to the amalgam group had a significantly higher mean (SD) urinary mercury level 5 years after baseline than did children assigned to the composite group (0.9 [0.8]; range, 0.1-5.7 µg/g of creatinine vs 0.6 [0.5]; range, 0.1-2.9 µg/g of creatinine, P
The interesting question is how did the non-amalgam treated group end up with so much mercury? Probably from vaccinations. At the time this study was done all children were getting a panoply of vaccinations all of which contained thimerosol, a mercury-containing preservative. These findings beg the question as to whether or not the study outcomes were truly valid since both groups had fairly significant levels of mercury.
The researchers looked at the changes in intelligence over five years in these children and found that, if anything, the group who had the amalgam fillings increased their intelligence more (my italics) than did those who didn’t get the mercury fillings.
Full-scale IQ, general memory index, and visuomotor composite scores increased between the baseline and 5-year assessments in both treatment groups. None of the differences between the change scores in the 2 treatment groups, adjusting for baseline score and randomization stratum, were statistically significant, although for all 3 tests, the differences favored the amalgam group (Table 3). Adjusting for additional covariates did not change the results appreciably.
There was no statistical difference in the intelligence changes between the two groups, but if the actual statistical analysis is examined an interesting thing pops out: the confidence intervals are huge. A large confidence interval means that the data was all over the place. Even though the differences overall were not statistically significant, based on the large confidence interval, many children were at the extremes. What this tells us is just what we would expect. Most kids aren’t affected by the amounts of mercury found in the amalgams, but some are. It’s these kids who are, who are much like the canaries in the mine shafts, whom we worry about. It’s like a pack of wolves or other predators circling a herd of elk; the young, old and sick (i.e., the most vulnerable) are the ones that get nailed. The strong, healthy elk aren’t bothered. It’s the same with a toxic insult such as mercury–it’s the vulnerable kids that are affected. Despite the fact that the averages don’t change, some kids can be adversely affected and not have it show up in a study such as this one.
The other study published in the same JAMA issue took place in Portugal where the researchers followed and compared two groups of children–one with mercury amalgams and one without–for seven years looking at memory, ability to focus, visuomotor functions and nerve conduction velocities. As in the first study the children with the amalgams had significantly higher levels of mercury in their tissues, but no statistically significant differences in the parameters of neurological function measured. And like the first study the confidence intervals were wide, indicating a wide distribution of findings. Once again, I’m sure some of the most vulnerable children had problems. It would have been nice to have seen all the data instead of just the tabulation.
In the most recent issue of The American Journal of Forensic Medicine and Pathology there appeared a paper throwing more light on this subject. As the researchers reported:
It rarely occurs that issues such as mercury, dental amalgam, or possible amalgam neurotoxicity may indeed reach the forensic scenario. However, scientific data have given us reason to at least consider the fact that dental amalgam may be a poison, in the strictest medicolegal sense, and that therefore its mode of distribution and accumulation within the body and consequential toxic effects could indeed have relevance from medicolegal perspective. However, much of the possible cause-effect concatenation still has to be proven, and the authors would like to briefly illustrate the results of the present pilot study to stimulate consideration of this issue, in other words as mere “food for thought.”
The authors of the study went on to describe the wealth of literature showing the correlation between mercury amalgams and tissue mercury levels. After summarizing the literature, they had this to say:
In essence, amalgam fillings have been shown to contribute to approximately two-thirds of the human body burden of mercury.
These researchers then analyzed the tissue mercury content of cadavers at autopsy and compared it to the number of mercury amalgam fillings. The reason this study is so important is that it is difficult to determine the amount of mercury in the tissues of living people because blood levels aren’t a particularly accurate way to measure it. Neither are urine and hair. Most of the mercury stays locked in the tissues, especially brain tissue, making it problematic to measure since most people aren’t eager to queue up for a brain biopsy, the only real way to find out.
Since corpses don’t much mind a brain biopsy the data these researchers uncovered is, in my opinion, invaluable. They found that there was a direct correlation between the number of fillings and the amount of mercury in the bodies. And they found that most of the mercury was in the brain with lesser amounts in the thyroid gland and kidneys.
As they put it:
Mercury levels increased with the number of dental amalgams for all the anatomic sites. The interaction term between each anatomic site and the number of occlusal amalgam surfaces was statistically significant (P = 0.03), suggesting that the association between mercury levels and the number of occlusal amalgams was dependent on the anatomic site. Mercury levels in the pituitary gland and the cerebral cortex in subjects with more than 12 occlusal amalgam surfaces were more than 10 times higher than levels in subjects with 3 or less occlusal amalgams (both P = 0.0007). Levels in the thyroid and in the renal cortex were respectively about 5 and 4 times higher in subjects with 12 occlusal amalgams or more compared with subjects with 3 occlusal amalgams or less (P = 0.01 and P = 0.04, respectively).
And their conclusions after a long discussion of the neurotoxic effects of mercury:
In summary, our research shows, for the first time, that frontal lobe cortex has the highest content levels of mercury associated with occlusal amalgam surfaces and total mercury levels approaching or exceeding 300 ppb (ng/g), wet weight, in some cases. This, in turn, strongly points to the hypothesis–which, in the future, should be looked into in larger and ad hoc studies–that mercury vapor, known to be a neurotoxicant, may indeed lead to some types of neurobehavioral disorders.
Now, I don’t know about you, but I’m not all that keen to have mercury amalgams. I may be one of those who can withstand the mercury; in fact, I probably am because I had mercury amalgams as a kid, but had them removed and replaced years ago. When I had them in place, they didn’t seem to do me any harm, but who knows, without them I might have become a rocket scientist.
I certainly wouldn’t expose any of my children or grandchildren to mercury amalgams just because JAMA came out with a couple of articles claiming that they were harmless. Mercury is toxic, of that there is no question. The amalgams produce mercury vapor, of that there is no question. People with mercury amalgams have higher levels of tissue mercury, of that there is no question. So why inflict children (or yourself) with a poison that is for sure going to go to their brains? Even though it might not harm them.
An even better method is to keep your children away from sugar and refined carbohydrates, make them practice good dental hygiene, and prevent cavities in the first place, then you won’t have that decision to make.