A new study suggests maternal prenatal exposure to naturally occurring lithium in drinking water is associated with a higher risk of autism spectrum disorder for offspring. The study is believed to be the first to identify naturally occurring lithium in drinking water as a possible environmental risk factor for autism.
Previous studies have shown ingestion of chronic and low-dose lithium from drinking water can influence the occurrence of adult neuropsychiatric disorders. Separate experimental research has also previously linked lithium to an important molecular pathway involved in neurodevelopment and autism. That’s why lead study author Beate Ritz was surprised to find that no study had yet been performed to assess whether lithium from drinking water consumed by pregnant women affects their child’s neurodevelopment.
“Any drinking water contaminants that may affect the developing human brain deserve intense scrutiny,” said Ritz, MD, professor of neurology and professor of epidemiology and environmental health at UCLA.
For the study, published in JAMA Pediatrics, Ritz and team analyzed lithium levels in 151 public water systems across all regions of Denmark. To identify which water system supplied mothers’ homes at the time of their pregnancy, the researchers used address information from Denmark’s civil registry system. The comprehensive databases identified 8,842 children diagnosed with autism spectrum disorder born between 2000 and 2013. The team also used that data to source 43,864 control participants, matched by birth year and sex.
Comparing the two groups, the researchers noted that as lithium levels increased, so too did the risk of an autism diagnosis.
Compared with the lowest quartile of recorded lithium levels—or those in the 25th percentile—lithium levels in the second and third quartiles were associated with a 24 to 26% higher risk of autism. In the highest quartile, the risk was 46% higher compared with the lowest quartile.
The researchers reported a similar relationship between increased lithium levels and higher risk of autism diagnosis when the data were broken down by subtypes of the disorder. They also found the association between lithium levels and autism risk was slightly stronger for those living in urban areas compared with smaller towns and rural areas.
The findings remained robust when the team adjusted for maternal characteristics, some socioeconomic factors and air pollution exposure, all of which have been linked to increased risk of autism in children.
In addition to Denmark’s databases, consumption of bottled water by Danes ranks among the lowest in Europe, meaning citizens largely rely on tap water—an ideal characteristic for this specific study. Additionally, the country has a robust system for measuring trace metals and other contaminants in their water supply. In general, lithium levels in Denmark’s water, when compared with other countries, are estimated in the low to moderate range.
“In the future, anthropogenic sources of lithium in water may become more widespread because of lithium battery use and disposal in landfills with the potential for groundwater contamination,” said Ritz. “The results of our study are based on high-quality Danish data but need to be replicated in other populations and areas of the world.”