As you read this post, I will be gallivanting around Italy and pretty much acting like I own the place. And I will definitely be trying this Italian food that people are always talking about. So just a quick post today. Divertitevi!
Can the water you drink while pregnant increase your child’s risk of autism?
I think readers will agree that mothers don’t have enough to worry about these days. Thankfully they can now add autism to the list of things that are their fault. Obviously I’m kidding, both because this isn’t something they should be worrying too much about but also because this is far from the first time that mothers have been implicated. In fact, people have attempted to blame mothers for autism for decades*.
A study run by researchers from Yale and UCLA was published in JAMA Pediatrics earlier this month that attempted to uncover a link between naturally occurring lithium in drinking water and the risk for autism. And though they did not claim that lithium exposure in drinking water causes autism directly, they did conclude that an association is possible:
Estimated maternal prenatal exposure to lithium from naturally occurring drinking water sources in Denmark was associated with an increased ASD risk in the offspring. This study suggests that naturally occurring lithium in drinking water may be a novel environmental risk factor for ASD development that requires further scrutiny.
I’m confident that in certain circles the results of this study will be wielded clumsily, despite the limitations that I will discuss shortly. It certainly wouldn’t be the first time that people eager to have an environmental factor to blame have latched on to preliminary findings. Some charlatans have even made careers out of it. But the major media coverage of this study has actually been good about calling for people to not jump to conclusions.
The researchers used data from Denmark, a country that is as loved for its appreciation of all things hygge as it is for the comprehensive nature of their public health records. Denmark also keeps excellent track of trace metals and other contaminants in their water supply and has one of the lowest rates of bottled water consumption in Europe. They are all that and a bag of Lego®! Who knew?
The study authors analyzed lithium levels in public waterworks in Denmark that provide drinking water to half the population. They were even able to match individual mothers to the source of their homes’ tap water during pregnancy. Using the nationwide database of patients with psychiatric disorders, they identified children born between 1997 and 2013 and compared 8,842 kids with an autism diagnosis to 43,864 without the diagnosis. They also controlled for a number of potentially confounding variables, such as maternal age, smoking during pregnancy, location, socioeconomic status, air pollution levels, and child’s sex.
After statistical analysis, they found that the risk of being diagnosed with autism increased with lithium levels in the drinking water:
Every IQR increase in estimated geocoded maternal exposure to natural source of lithium in drinking water was associated with higher odds for ASD in offspring (OR, 1.23; 95% CI, 1.17-1.29). Elevated odds among offspring for ASD were estimated starting from the second quartile (7.36 to 12.67 μg/L) of estimated maternal exposure to drinking water with lithium and the OR for the highest quartile (more than 16.78 μg/L) compared with the reference group (less than 7.39 μg/L) was 1.46 (95% CI, 1.35-1.59).
So as lithium levels increased, so did the risk of an autism diagnosis. When compared to the lowest quartile of recorded lithium levels, lithium levels in the second and third quartiles were associated with a 24-26% higher risk of autism. In the group of children potentially exposed to the highest lithium levels, the risk was 46% higher compared to the lowest quartile. There were, of course, some limitations in the analysis.
Our study also has several limitations. First, this registry study lacks information on dietary and lifestyle factors, including habits of water consumption. This study did not measure the actual sources of water the mothers consumed and did not consider childhood exposure.
They also raise the possibility of other trace elements, such as iodine, that could have contributed to neurodevelopmental problems. Iodine levels do often track with lithium levels in natural sources of water. In my opinion, however, that is an unlikely confounding variable because though hypothyroidism can be caused by excess iodine exposure, and hypothyroidism can cause developmental problems, it is screened for in Danish newborns.
This could be a situation not unlike the classic correlation between ice cream and drowning risk. It would be helpful in this case to have had actual blood levels of lithium in these mothers, or even a potential mechanism of action to increase the plausibility of the study findings. As it stands, we don’t even really know how lithium works in people with psychiatric disorders such as bipolar disorder and depression let alone how it could harm neurodevelopment. Which brings up another potential problem with the study.
People with certain psychiatric disorders are treated with lithium and sometimes these people are pregnant. Lithium as a prescribed medication, which would result in much higher levels in the blood of a pregnant person than from drinking water, has been around for a long time and there is actually a decent amount of safety data that has looked at the potential impact on the developing fetus. Cardiac defects, though still not common, are the problem we worry about the most. There is less data on long term neurodevelopment, but what we have has been reassuring.
Conclusion: Don’t throw the tap water out with the lithium?
Lithium in drinking water is not regulated in the United States, and there are no established standards for how much is safe. Within the past two years, however, it has begun to be monitored more closely. Most of the data on adverse outcomes related to exposure come from people taking lithium as a medication and the amount ingested in drinking water and food (cereals, potatoes, tomatoes, cabbage) is a fraction of that.
Still, we don’t know what causes autism, though there is clearly a large genetic component as demonstrated in studies of twins. It is likely the result of a combination of genetic and environmental factors leading to a variety of changes in the brain that we have given the autism label, and it is definitely possible that exposure to lithium in drinking water played a role in some children with the diagnosis. This study is interesting, and it should be followed up.
In the meantime, I don’t see this as a reason for pregnant people to panic or to avoid tap water entirely. But I also wouldn’t hold it against someone who chooses to do so, although not everyone has the means to live off of bottled water for several months. And, of course, there is often plenty of lithium in bottled water as well. So they would need to do their homework. And because few things in health, and life, are simple and straightforward, there have also been studies linking lithium in drinking water to improved psychiatric outcomes in adults.