Where is lithium used in the body?

Lithium is a naturally occurring alkali metal, which living organisms ingest from dietary sources and which is also present in trace amounts in the human body. In much higher concentrations, lithium is effective as a medication for mania and mood swings including manic depressive disorders

radioactive decay occurs in unstable atomic nuclei – that is, ones that don't have enough binding energy to hold

the nucleus together due to an excess of either protons or neutrons.