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Posted by Sylvia on Friday, February 06, 2004 (16:55:42)
AWARES 05/02/2004
source Northeastern University, Health DayNews and CanWest News Service
BOSTON, Massachusetts, USA: Exposure to certain neurodevelopmental toxins, including the mercury-based vaccine additive, thimerosal, may increase the risk of autism and attention-deficit hyperactivity disorder, says a study in the April 2004 issue of the journal, Molecular Psychiatry.
This research, which was rushed into print online on February 5 - two months ahead of its scheduled publication - is the first to offer a possible explanation for possible causes of these two increasingly common childhood disorders.
The researchers at Northeastern University in Boston, together with colleagues from Tufts University, also in Boston, from the University of Nebraska and from Johns Hopkins University in Baltimore, found that exposure to toxins such as ethanol and heavy metals (including lead, aluminum and the ethylmercury-containing preservative, thimerosal) interrupt growth factor signalling.
This adversely impacts methylation reactions such as the transfer of carbon atoms. Methylation is critical to proper neurological development in infants and children.
"Scientists certainly acknowledge that exposure to neurotoxins like ethanol and heavy metals can cause developmental disorders but, until now, the precise mechanisms underlying their toxicity have not been known," the researcher and pharmacy professor, Dr Richard Deth, of Northeastern University, says in a prepared statement. "The recent increase in the incidence of autism led us to speculate that environmental exposures, including vaccine additives, might contribute to the triggering of this disorder."
Starting in 2000, the United States and Europe largely phased out thimerosal, often used as a preservative in multi-dose units of vaccines for diseases such as hepatitis, whooping cough, tetanus and diptheria.
Now, most vaccines in the United States and Europe contain only trace amounts of thimerosal. However, multi-dose flu vaccines still contain thimerosal. The same is true of many larger, multi-dose vials of vaccines shipped to and used in developing countries.
Though some speculation exists regarding this link, Dr Deth and his colleagues found that exposure to toxins, such as ethanol and heavy metals (including lead, aluminium and thimerosal) potently interrupt growth factor signalling, causing adverse effects on methylation reactions (that is the transfer of carbon atoms).
Methylation, in turn, plays a significant role in regulating normal DNA function and gene expression and is critical to proper neurological development in infants and children. Scientists and practitioners have identified an increase in diagnoses of autism and ADHD in particular, though the reasons why are largely unknown.
In their work, the scientists found that insulin-like growth factor-1 (IGF-1) and the neurotransmitter, dopamine, both stimulated folate-dependent methylation pathways in neuronal cells. At the same time, they noted that compounds like thimerosal, ethanol and metals (like lead and mercury) effectively inhibited these same biochemical pathways at concentrations which are typically found following vaccination or other sources of exposure.
By better understanding, what happens when infants and children are exposed to these materials, the work of Deth and his colleagues helps to explain how environmental contact with metals and administration of certain vaccines may lead to serious disorders which manifest themselves during childhood, including autism and ADHD.
Full Article
"Scientists certainly acknowledge that exposure to neurotoxins like ethanol and heavy metals can cause developmental disorders, but until now, the precise mechanisms underlying their toxicity have not been known," said Dr Deth. "The recent increase in the incidence of autism led us to speculate that environmental exposures, including vaccine additives might contribute to the triggering of this disorder."
Thimerosal, which was largely phased out in the United States and in Europe starting in 2000, was often used for its preservative abilities in multi-dose units of vaccines for diseases like hepatitis, whooping-cough, tetanus and diptheria.
Today, most vaccines carry only trace amounts of it, according to the Atlanta-based Centers for Disease Control and Protection (CDC). But in larger, multi-dose vials of these vaccines, often shipped to - and used in - Third World countries, thimerosal is still very common. Multi-dose flu vaccines still contain thimerosal.
Additionally, the scientists recently obtained more insight into the mechanism by which thimerosal interferes with folate-dependent methylation. It acts by inhibiting the biosynthesis of the active form of vitamin B12 (methylcobalamin), which is of particular interest because doctors treating autistic children are having good success with the administration of methycobalamin.
Large amounts of vitamin B12 - which is found in poultry, fish and fish oil - helps to reduce the levels of homocysteine, which injures neurons and blood vessel walls, and stimulates the genes associated with neural regeneration.
However, one of Canada's leading experts in vaccination says that large studies have repeatedly failed to find any association between brain damage and vaccines that do, or do not, contain thimerosal.
"What [the researchers] are doing in the test tube may, or may not, have any relationship to what happens in the body," said Dr Ronald Gold, professor emeritus of pediatrics at the University of Toronto and author of the book, "Your Child's Best Shot: A Parent's Guide to Vaccination."
Dr Gold said that there was no evidence that the low doses of thimerosal which the researchers tested would even cross a child's blood-brain barrier.
But Dr Deth thinks there may be a link, and he believes that thimerosal may play a role for the one out of 200 children who will experience some kind of developmental disorder.
"I don't want to impair the public-health importance of vaccine programmes. It's not the vaccines that are the problem - it's the additives that are the problems," said Dr Deth. "Some would consider [thimerosal] a smoking gun. I think it is."
In Canada, thimerosal had been used to prevent the growth of bacteria or fungi in multi-dose units of vaccines for diseases such as hepatitis and diphtheria, pertussis (whooping cough) and tetanus, or DPT.
Four Canadian provinces - Ontario, Nova Scotia, Newfoundland and P.E.I - have not used childhood vaccines containing thimerosal since the early 1960s, when they switched to a DPT vaccine that was combined with the killed polio vaccine. (Thimerosal could not be used with the combined shot because it destroyed the efficacy of the polio vaccine.)
All other Canadian provinces, including British Columbia, began to move to thimerosal-free vaccines starting in 1997. As of March 2001, all vaccines for routine immunisation of children in Canada have been available without thimerosal.
But the annual 'flu shot - which Canadian doctors this year began pushing on even healthy children over six months of age - contains the preservative. And thimerosal is still found in larger, multi-dose vaccines shipped to Third World countries.
Dr Laszlo Palkonyay, a medical-scientific adviser for the Quebec-based 'flu-vaccine maker, Shire Biologics, noted that a study published in the journal, Pediatrics, in September 2003, which was based on a registry of all psychiatric admissions in Denmark between 1971 and 2000, had found no trend toward an increase in autism rates during the period in which thimerosal was used in vaccines in that country. In fact, Dr Palkonyay said, the incidence of autism had increased after the preservative was removed from vaccines in 1990.
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