Lithium and the Brain-Bone Axis: A Bridge between Osteoporosis and Alzheimer's Disease

We evaluate the converging evidence positioning lithium as a systemic modulator of bone and brain health through shared molecular pathways. This review examines the molecular basis, preclinical data, and clinical observations suggesting that lithium-long established as first-line therapy for bipolar disorder-may simultaneously protect against osteoporosis and neurodegeneration as two clinical conditions increasingly recognized to share biological substrates.

Lithium inhibits glycogen synthase kinase-3β (GSK-3β), stabilizes β-catenin, and activates Wnt signaling in neurons and osteoblasts, while also modulating calcium-inositol homeostasis and suppressing NF-κB-mediated inflammation. Large observational studies report lower dementia incidence and reduced fracture risk in long-term lithium users, together with increases in bone mineral density. Declining brain lithium concentrations in patients with Alzheimer's disease raise the hypothesis that lithium may act as an essential micronutrient rather than solely a pharmacological agent. Bidirectional brain-bone crosstalk involving osteocalcin signaling and sclerostin transport across the blood-brain barrier provides a mechanistic basis for these pleiotropic effects. Lithium offers a unique paradigm for understanding and potentially treating age-related decline in multiple organ systems at subclinical dosage and concentration. However, observational study limitations, optimal dose uncertainties, and toxicity related to long-term usage concerns necessitate rigorous randomized controlled trials before broader clinical recommendations can be made. Future research should focus on optimizing formulation and patient selection to realize lithium's dual protective potential for bone and brain while minimizing risk.