Baby teeth from autistic children hold higher levels of 19 potentially toxic chemicals in a small pilot

According to the study as reported by ScienceAlert, 95 percent of the 60 compounds common enough to compare ran higher in the autism group ^[9]. That comes to 57 compounds ^[19]. Only 19 of the differences passed statistical significance ^[9], about a third of the panel ^[20]. When nearly a whole panel moves in one direction, two readings fit. Particular chemicals could differ between the groups, or the children with autism could have had more exposure overall, with most compounds rising together. With 22 cases and 16 controls ^[5], the data cannot separate those. The reported account does not describe how the controls were matched, or whether the tests were adjusted for comparing 60 compounds at once ^[8].

Household habits are one plausible source of a shared difference. Benzyl benzoate, the compound with the largest gap, goes into personal care products, gets added to food and is used to treat lice and scabies ^[11]. How much of it reaches a child depends partly on what a household buys. A pilot this size cannot rule out that something about the households lies behind both the chemical levels and the diagnosis. ScienceAlert notes that the findings do not show any of these chemicals causes autism, and the researchers call the work a small pilot ^[17].

I'd expect the method to outlast this list of 19, provided larger studies reproduce the measurements. Blood and urine hold a chemical's signature for a short window, sometimes only hours ^[2]. "Teeth capture cumulative exposures over long periods of time, whereas blood or urine samples only show a specific window of time," said Lynne Heilbrun, an environmental scientist at the University of Texas at San Antonio and the study's first author ^[3]. "We need both," she said ^[3].

The tooth record has limits of its own. It begins around the fourth fetal month, when primary teeth start to form, and ends near age three, when formation completes ^[1]. That start date falls after the first trimester, the period Heilbrun singles out. "There are several critical windows of exposure during pregnancy, especially in the first trimester, but it doesn't stop there," she said. "The central nervous system continues to develop after birth until around age 25." ^[4]

The researchers' broadest conclusion rests on the whole sample, cases and controls together. "Our study suggests that children are being chronically and repeatedly exposed to a wider range of developmental toxicants than previously identified in short-term exposure studies," they wrote ^[13]. They also judge maternal exposure "likely substantial," because pregnant and lactating women increase their food and water intake ^[14]. The measurements were made on children's teeth, so that maternal estimate is the authors' inference. They note that many of the toxicants identified target the brain, liver and mitochondria ^[15], and say further studies are warranted ^[18].