Researchers at the National Institutes of Health found more toxic lead and less of essential nutrients zinc and manganese in the teeth of the kids with autism. Interestingly, they used the teeth of 32 sets of twins, and 12 individual twins (either one had autism, or both or neither did) for this study, which is published in the journal Nature Communications, and were therefore able to control for almost all genetic factors.
Cindy Lawler, Ph.D., chief of the NIEHS Genes, Environment, and Health Branch, explained via email, “We know from previous studies that pregnant or breastfeeding women should minimize their exposure to lead and other toxic substances. When the mom is exposed, the baby may be exposed as well. And for lead in particular, there is no safe exposure level.”
Specifically, kids with autism were found to have higher levels of lead and manganese during the period after birth. They also exhibited lower zinc levels earlier in utero; then following birth, the levels increased as compared to kids without autism. The biggest differences in the levels were noted in the instances in which just one twin had autism.
Lawler commented in a press release, "We think autism begins very early, most likely in the womb, and research suggests that our environment can increase a child's risk. But by the time children are diagnosed at age 3 or 4, it's hard to go back and know what the moms were exposed to." She adds, "With baby teeth, we can actually do that."
Both this study and previous ones have indicated that exposure to heavy metals can be toxic for brain development at high levels, and is linked to autism and its severity. It's worth noting, though, that many factors may play a role in a child's risk of developing autism.