The new research may offer a clearer picture on whether mercury plays a major role in causing autism. Researchers at University of California - Davis say the study shows children with autism do not metabolize mercury differently.

"Children with autism and children with typical development have the same levels of mercury in their blood after we adjusted for variable intake, variable sources, like fish consumption,” said Irva Hertz-Picciotto of UC-Davis’ Mind Institute.

The findings are part of an overall study designed to identify autism-related factors and their origins. Doctors who treat children with autism say the results are important to the medical world and parents.

"Mercury does not result in autism; it results in other issues but not in autism,” said Dr. Max Wiznitzer of Rainbow Babies and Children’s Hospital.

Mercury is a heavy metal known to cause adverse developmental effects when consumed in excess amounts. Fish is a major source of mercury but doctors say, if eaten in moderation, it is an important part of a healthy diet.

"The amount of mercury exposure that you would get in comparison to the health benefits from the nutritional aspects of the fish clearly tilts the balance in favor of the nutritional aspect,” said Wiznitzer.

Researchers say the results of the study are just one piece of the puzzle of understanding autism. While more studies are needed on the effects of mercury, researchers say other minerals and chemicals in the water, air and household products could hold clues to what causes autism.

“We need to cast a very wide net and really look broadly at all sorts of things that are in the environment,” said Hertz-Picciotto.

With each study, researchers hope to unlock the mystery of autism.

Researchers also said kids who'd had vaccines containing mercury were no more likely than other kids to have elevated levels of mercury.