Study leader James Adams, who directs the Arizona State University Autism/Asperger's Research Program, said the study involved 55 children with autism ages 5-16 compared to 44 controls of similar age and gender.
The study, published in the journal Biological Trace Element Research, found the autism group had significantly higher levels -- 41 percent -- of lead in their red blood cells and 74 percent higher urinary levels of lead, 77 percent higher levels of thallium, 115 percent higher levels of tin and 44 percent higher levels of tungsten.
Lead, thallium, tin and tungsten are toxic metals that can impair brain development and function, and also interfere with the normal functioning of other body organs and systems, Adams said.
A statistical analysis was conducted to determine if the levels of toxic metals were associated with autism severity, using three different scales of autism severity.
The study found 38 percent to 47 percent of the variation of autism severity was associated with the level of several toxic metals, with cadmium and mercury being the most strongly associated.
"We hypothesize that reducing early exposure to toxic metals may help ameliorate symptoms of autism, and treatment to remove toxic metals may reduce symptoms of autism; these hypotheses need further exploration, as there is a growing body of research to support it," Adams said in a statement.