Mercury does not cause autism, another study now concludes.
The levels of mercury in the urine of children with autism were no higher than urine mercury levels of children without the condition, the study from England found.
The discredited idea that the form of mercury, called ethylmercury, sometimes used in vaccines may lead to autism has led to reductions in vaccine rates and increases in cases of preventable diseases, such as measles and mumps, according to the study.
But rates of autism have continued to rise after the use of the thimerosal in children's vaccines was stopped in 2001 in the developed world, according to the study.
The researchers collected urine samples from 54 children with autism spectrum disorders, and compared these with three other groups: 115 children from the general population, 28 children who attended special schools (mainly because of learning disabilities), and 42 children who didn't have autism, but had a sibling with the condition.
There were no differences, between any of the groups, in the concentration of mercury found in the urine. The researchers also noted that tests for other heavy metals — such as lithium, manganese, cadmium and lead — were also the same across all the groups.
Previous studies have shown that the form of mercury, called ethylmercury, sometimes used in vaccines, cannot cross the blood-brain barrier. The form of mercury that has been linked to nervous system problems, called methymercury, can enter the brain from the blood.
Previous studies that have looked at the urine mercury levels in children with autism have yielded mixed results, but those had involved testing the urine of children who had received chelation treatments, which lowers the level of mercury and other metals in the blood.
Chelation treatments, which are sometimes given to children based on the idea that they may treat autism or improve its symptoms, may pose risks to children's health.
The study was limited in that it included a relatively small number of children, the researchers wrote. It also could have been improved by using urine collected over a 24-hour period, rather than a single sample from each child, but 24-hour collections are difficult to accomplish, according to the study.
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