Does a low dose of lithium help protect the ageing brain?

Lithium reaches the brain even at a very low dose. A pilot study involving nine healthy men showed that 5 mg of lithium per day (roughly 2 to 7% of a therapeutic dose) was measurably present in brain tissue after two to four weeks. This demonstrates reachability, not effectiveness.

A population study covering 62 million Americans found that areas with higher lithium levels in the drinking water had a slightly lower prevalence and incidence of dementia (approximately 3.5 to 4% less). That sounds reassuring, but this type of research can never prove that lithium is the cause. Coincidental differences between regions can distort the picture. The same study also found a slightly increased mortality among dementia patients in areas with high lithium levels, although that association partly disappeared after statistical correction.

In people with early Alzheimer's disease or mild cognitive impairment, several small studies and one systematic review from 2014 describe that low lithium doses may slow cognitive decline and produce favourable changes in certain cerebrospinal fluid markers. In animal research, lithium inhibits two central features of Alzheimer's disease: the accumulation of amyloid plaques and abnormal tau proteins. However, results in clinical studies in humans are mixed, and no large randomised trials have yet been conducted.

An important point of concern from mouse studies: a higher lithium dose (equivalent to approximately 500 mg per day in humans) actually worsened memory and brain activity, whereas a lower dose given in combination with an antipsychotic showed beneficial effects. This points to a narrow safety window. Experts also stress that precise blood level monitoring and careful patient selection are essential given lithium's well-known toxicity. Casually taking low-dose lithium supplements without medical supervision is therefore risky.