Lithium is a medication approved for the treatment of bipolar disorder, but a new study suggests that its therapeutic benefits may not stop there. Researchers have uncovered a link between lithium in drinking water and reduced risk of dementia.

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Researchers have found a link between lithium in drinking water and reduced risk of dementia.

Dementia is fast becoming one of the world's most burdensome illnesses. According to the World Health Organization (WHO), there are currently around 47 million people across the globe living with dementia, and this number is expected to reach 75 million by 2030, and 132 million by 2050.

Alzheimer's disease is the most common form of dementia, accounting for around 60 to 80 percent of all cases.

While there are medications that can help to improve symptoms of dementia, there are currently no approved treatments that can slow progression of the disease or cure it. Given the projected global increase in dementia incidence, there is a desperate need to identify such treatments.

The new study - recently published in JAMA Psychiatry - suggests that lithium could be a potential candidate for dementia prevention.

Lithium and dementia risk

While lithium is used to reduce manic episodes in people with bipolar disorder and other mental illnesses, it is first and foremost a chemical element that is naturally present in drinking water in many parts of the world.

Study co-author Dr. Lars Vedel Kessing, of the University of Copenhagen in Denmark, and team set out to determine whether there might be a link between exposure to lithium in drinking water and the risk of dementia.

The team analyzed data from a Danish population-based registry, including 73,731 adults who had been diagnosed with dementia between 1995 and 2013, alongside 733,653 adults who did not have dementia.

The researchers also analyzed drinking water samples retrieved from 151 waterworks in Denmark, which supply water to around 42 percent of the country's population.

By calculating the lithium content in each of the water samples and tracking the residential addresses of each participant, the researchers were able to estimate the subjects' mean lithium exposure since 1986.

Compared with adults who had not been diagnosed with dementia, adults who had received a dementia diagnosis were found to have been exposed to lower levels of lithium in drinking water.

In detail, the researchers found that the incidence of dementia was 17 percent lower for adults whose lithium exposure was 15 micrograms per liter or higher, compared with adults exposed to 2 to 5 micrograms per liter.

However, the team notes that the association between exposure to lithium in drinking water and dementia risk was non-linear; adults exposed to 5.1 to 10 micrograms of lithium per liter were found to be at greater dementia risk than those exposed to 2 to 5 micrograms per liter.

A 'golden public health intervention'?

The authors point to a number of study limitations. For example, they did not account for participants' access to healthcare services, which could influence the likelihood of a dementia diagnosis.

"Furthermore," the researchers write, "because all inhabitants in a given municipality are assigned the same level of lithium exposure, it cannot be excluded that other, unobserved environmental or social care factors related to individuals' municipality of residence might have confounded the association between lithium exposure and dementia rate."

Additionally, it is possible that the levels of lithium in water supplies changed during the study period, which may have skewed the findings. However, the team notes that because of lithium's slow release from soil and sediment, it is more likely that lithium levels remained stable.

In an editorial linked to the study, Dr. John J. McGrath, of the University of Queensland in Australia, and Michael Berk, Ph.D., of the University of Melbourne, also in Australia, say that the results should be interpreted with caution.

"That said, the prospect that a relatively safe, simple, and cheap intervention (i.e., optimizing lithium concentrations in the drinking water) could lead to the primary prevention of dementia is a tantalizing prospect," they write.

"If the findings of Kessing and colleagues are supported in future studies, even a marginal reduction in the incidence of dementia could result in major societal and economic gains."

"In the spirit of alchemy, could we convert lithium, a simple metal used as a mood stabilizer, into a golden public health intervention that could prevent dementia? This will depend on what the next generation of epidemiologic studies and clinical trials reveal."