Here’s the latest candidate for an exposure in pregnancy that causes autism.
Is there autism in the water?
Danish researchers, noting the increase in the incidence of autism spectrum disorder (ASD) over the past few decades, decided to test if prenatal exposure to lithium in drinking water had increased the chances of babies developing ASD.
They didn’t pick lithium by closing their eyes and stabbing at the periodic table: maternal therapeutic use of the metal has, they say, been associated with adverse birth outcomes and lithium does act on a signalling pathway involved in neurodevelopment.
The research, published in JAMA Paediatrics, is accompanied by an editorial, which points out that it’s not the first time chemicals in the environment have been linked to ASD, citing air pollution, pesticides, metals and phthalates as possible aggravators.
The researchers analysed data from participants in the Danish Medical Birth Registry who were diagnosed with ASD and born from 2000 through 2013, identifying 8842 eligible children. They were compared with 43,864 control participants matched by birth year and sex. The data were analysed from March 2021 through November 2022.
Geocoded maternal residential addresses during pregnancy were linked to lithium level (range, 0.6-30.7 micrograms per litre) in drinking water estimated based on 151 waterworks measurements of lithium across all regions in Denmark.
They found every interquartile range increase in exposure was associated with higher odds of the disorder in offspring, with an odds ratio of 1.23.
“The associations were unchanged when adjusting for air pollution exposures and no differences were apparent in stratified analyses,” they wrote.
The authors cautiously concluded that “naturally occurring lithium in drinking water may be a novel environmental risk factor for ASD development that requires further scrutiny”.
But for me, all this prompts the question: is pregnancy the critical moment when it comes to ASD risk?
As the editorial author David Bellinger wrote: “Children presumably consumed the same water throughout childhood as their mothers had during pregnancy, so any effect of lithium in water on ASD risk could be the result of cumulative exposure in the entire period prior to diagnosis and not just exposure during pregnancy. Also, if lithium concentrations in water have remained stable over decades, it is unlikely that lithium exposure has contributed to the recent rapid increase in ASD incidence.”
Lithium in water has also been linked to health benefits – “specifically reductions in rates of hospitalization for psychiatric disorders and suicide”, somewhat unsurprisingly given what we prescribe lithium for.
ASD is a complex set of symptoms. There is nothing to suggest that causes, associations, pathways and mechanisms associated with it won’t be equally complex.
As Dr Bellinger writes in conclusion:
“Until the basic biology of ASD is better understood, it will be difficult to distinguish causal from spurious associations.”
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