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Scientists may have found a way to limit the risk of developing dementia by drinking tap water.

There’s a hitch, of course: The tap water has to contain lithium, according to a recently published Danish study. Lithium is already being put to use in various psychiatric medications, but the new research focused on the levels occurring naturally in British water supplies.

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The 18 year project compared cumulative lithium exposure over time between people with dementia diagnoses and those without. The results initially seem encouraging: the group without dementia had consumed, on average, more lithium than the group with dementia. This seems to indicate that lithium could be protective against the disease.

Scientists have found that drinking tap water with lithium may limit the risk of developing dementia.

While this pattern was promising, it wasn’t completely consistent. The study also grouped subjects by their levels of lithium consumed. The population with the highest levels of lithium exposure had the lowest incidence of dementia diagnoses, but one of the intermediate groups—not the lowest interval, as expected—actually had the highest rates of dementia among all groups in the study. Why that happened isn’t clear, and Dr. Brent Forester, who was interviewed by Reuters, called it “a worrisome sign” that suggested something besides lithium may be responsible for the spike in dementia rates.

That unexplained result has given researchers pause. Experts seem to agree that any immediate changes to current treatments would be premature. King’s College London’s Dr. Allan Young told the Telegraph the following:

This study fits well with previous evidence which shows that environmental lithium may have health benefits and lithium may prevent dementia…Although some may say that lithium should be ‘added to the water’ the first step might be to conduct clinical trials to examine the preventative effects of lithium first.

Inconsistencies and all, the magnitude of the study is compelling. The data was amassed from approximately 800,000 individuals. And while there aren’t any conclusive policy recommendations that can be drawn from the findings, they do provide a strong foundation for more investigation into dementia and the role lithium may play in its treatment or prevention.