Study finds that lithium loss triggers Alzheimer’s, but a lithium-based compound reverses the disease in mice.

What sets off the earliest chain of events that leads to Alzheimer’s disease? And why do some people who show Alzheimer’s-like brain changes never progress to dementia? These unresolved questions have challenged scientists for decades.

Researchers at Harvard Medical School now believe they may have an explanation: a deficiency of lithium in the brain.

Their study, published on August 6 in Nature, demonstrates for the first time that lithium is naturally present in the brain, where it protects against neurodegeneration and supports the normal functioning of all major brain cell types. The findings — a decade in the making — draw on mouse experiments as well as analyses of human brain tissue and blood samples from people at different stages of cognitive health.