Contrary to previous research, lithium levels in groundwater don’t protect against bipolar disorder

High lithium levels existing in groundwater don’t decrease the risk of bipolar disorder or dementia, according to a new population epidemiology study in JAMA Psychiatry.

“Therapeutic lithium doses are orders of magnitude larger than groundwater lithium concentrations, making a true causal relationship between groundwater lithium and mental health biologically dubious,” wrote corresponding author William F. Parker, MD, Department of Medicine, The University of Chicago, Chicago, IL, and coauthors.

Lithium is a trace metal that occurs naturally in groundwater. In addition to its use in treating bipolar disorder, lithium also may be clinically useful in dementia.

Some previous research supports a potential protective role of lithium due to environmental exposure. For instance, in the United States, low levels of lithium in drinking water have been statistically linked to lower rates of mental illness. Furthermore, researchers in Denmark have previously shown a negative correlation between lithium levels in drinking water and dementia.

Nevertheless, psychiatric diagnoses vary widely in relation to local demographics and health-care resources. These local variables could confound any association between lithium levels in water and the frequency of mental disorders.

To account for this, the researchers examined the association between groundwater lithium and diagnoses of bipolar disorder and dementia in the United States, adjusting for local health care resources and demographics.

The team examined claims data representing 4,227,556 adults living in 174 counties, including 404,662 adults living in 32 counties with high lithium levels (>40 μg/L) in the groundwater. They also looked at county-level health-care resources and demographics.

Ground water lithium levels were assessed by the US Geological Service between 1992 and 2003. The mean lithium concentration in all counties was 27.4 μg/L (median 11.1 μg/L).

Dr. Parker and colleagues used weighted variables based on county-level health-care resources, and designed the study to confer low- and high-lithium counties an equivalent distribution of health-care resources. Finally, the team controlled for sex, payer, and county-level demographics.

The researchers found that high lithium levels did not provide any benefit with regard to bipolar disorder or dementia. Furthermore, no benefit was seen with any of the three negative controls—major depressive disorder, myocardial infarction, or prostate cancer.

“In our study,” reflected the researchers, “the high-lithium group was exposed to a mean of 141.3 μg/L in their water supply. This means that a patient would need to drink more than 1,000 L of water a day to ingest the lowest reported effective therapeutic lithium dose of 150 mg.”