In a major new finding almost a decade in the making, researchers at Harvard Medical School say they’ve found a key that may unlock many of the mysteries of Alzheimer’s disease and brain aging — the humble metal lithium.

Lithium is a metal found in some foods, drinking water, and in trace amounts in our bodies. It has long been used to treat some psychiatric disorders. But its potential role in protection against brain aging and Alzheimer’s disease opens up new doors for developing medicines that may finally provide an effective tool for fighting this dreaded brain-robbing disease,

A few limited clinical trials of lithium for Alzheimer’s disease have shown some efficacy, but the lithium compounds they used — such as the clinical standard, lithium carbonate — can be toxic to aging people at the high doses normally used in the clinic.