Autism is a distressing condition and five children in every 10000 are afflicted with it, and of these the ratio of 4 boys to 1 girl.* What causes a seemingly normal baby to develop autism is still unknown, but many in the USA believe that mercury is the cause. In the late 1990s it was accused of causing attention deficit syndrome, stammering, and especially autism. Some thought that thimerosal was to blame. This is a mercury-containing antibacterial agent which was added to vaccines to preserve them. The US Centers for Disease Control and Prevention first reported a link between thimerosal and mental development in children after carrying out an epi-demiological study, although they later admitted that their analysis was flawed. Nevertheless, as a result of a Congressional report many US vaccines phased out its use from 2000 onwards and they no longer contain this preservative. Japan and most countries in Western Europe have done likewise.
Thimerosal is an organo-mercury compound and there are several such compounds which vary according to the organic group attached to the mercury atom. Some, such as methyl mercury, have caused widespread illness in the past, as we shall see. Thimerosal is an ethyl mercury compound and by virtue of this it is believed to be safe (see Glossary for more about thimerosal). It was introduced in the 1930s by the pharmaceutical company Eli Lilly, and used originally as a preservative for veterinary vaccines, and then to safeguard human vaccines. There are claims that it was never properly tested for safety in humans.
In the UK thimerosal continued to be used because there is no firm evidence that it was anything other than safe, although parents could request that their offspring be injected with mercury-free vaccines. Indeed an analysis of the medical history of 100000 children born between 1988 and 1997 in the Thames region showed no correlation between autism and exposure to thimerosal. An even larger survey of the 467450 babies born in Denmark between 1990 and 1996 came to the same conclusion. The amount of thimerosal in a single vaccine is less than 5 ^g, and is well below the level that
* In the 1990s it appeared that the incidence of autism was increasing, although in 2004 it was discovered that the increase was mainly due to other childhood problems now being more correctly diagnosed as autism. When Hershel Jick of Boston University School of Medicine analysed various behavioural disorders among American children he discovered that these had declined as the diagnoses of autism had increased.
some believe to be dangerous, although on a weight-for-bodyweight basis it is near the maximum recommended for pregnant women and those who are breastfeeding. The amount certainly exceeds the guidelines set by the Environmental Protection Agency.*
Surprisingly, a study of mercury levels in the hair of babies who were later diagnosed as autistic, showed there to be much less mercury present than in the hair of children who do not develop autism. This work was done by a group in Louisiana led by Amy Holmes who expected to find just the opposite when she started the study, believing that mercury levels would be higher in autistic children. She had contacted the parents of some autistic children and asked if they had saved samples of hair from their baby the first time it was cut. Several of them had, and sent it to her, but when Holmes analysed these for mercury she could find very little. She widened her survey to include the first hair of 94 autistic children, and compared what she found with the hair from 45 non-autistic children. The average level of mercury in this latter group was 3.6 ppm, but that of the autistic children was only 0.47 ppm, and indeed Holmes found the more severe the autism the less mercury there was, with the most severely disabled having only 0.2 ppm on average.
So what do Amy Holmes's findings mean? Those who believe that mercury is the cause of autism explain the low amounts in hair by speculating that children who develop autism have a genetic defect that makes them unable to remove mercury from their bodies which then tends to collect in the brain where it does its damage. They might be right. Until we truly understand the causes of autism, which may in fact be due to several factors, such as parental neglect, faulty genes, illness, or physical damage to the brain, then we cannot rule out mercury. Yet all babies come into this world with some mercury in them, because mercury is a natural part of everyone's diet and a pregnant woman cannot avoid taking some in and passing it to her foetus. To avoid vaccinating a baby, because of the minute amount of extra mercury it will receive, it is more likely to put a baby's health at risk than its not having that vaccine.
* The UK Government's Department of Health announced in August 2004 that thimerosal was no longer to be used in vaccines.
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