Trace amounts of lithium in drinking water may reduce a population's suicide rates, according to an analysis conducted by researchers from the universities of Oita and Hiroshima, Japan, and published in the British Journal of Psychiatry.

But mental health advocates warned against adopting plans to add the element to public drinking water supplies, as in controversial water fluoridation programs.

Lithium is a naturally occurring element that has long been used for the treatment of bipolar disorder. Unlike conventional antidepressants, lithium stabilizes moods at both extremes of the spectrum -- depression and mania. Research conducted on data collected in the 1980s has previously suggested that communities with higher concentrations of lithium in their tap water might have lower suicide rates than communities with lower levels.

To follow up on this research, scientists measured the levels of lithium in the drinking water of 18 different municipalities in the Japanese prefecture of Oita, finding concentrations ranging from 0.7 to 59 micrograms per liter. They then compared these numbers with the suicide rates in each community.

The researchers found that suicide rates were lowest in municipalities with the highest concentrations of lithium in the water.

"Our study suggests that very low levels of lithium in drinking water can lower the risk of suicide," the researchers wrote. "Very low levels may possess an antisuicidal effect."

Sophie Corlett of the mental health nonprofit Mind greeted the findings with caution.

"We already know that lithium can act as a powerful mood stabilizer for people with bipolar disorder, and treating people with lithium is also associated with lower suicide rates," she said. "However, lithium also has significant and an unpleasant side effects in higher doses, and can be toxic. Any suggestion that it should be added, even in tiny amounts, to drinking water should be treated with caution and researched very thoroughly."

There is a very small difference between a clinical and a toxic dose of lithium.