Why is adequate sodium important for patients on lithium?

• A. To prevent lithium toxicity by balancing renal reabsorption
• B. To increase lithium absorption
• C. To decrease lithium effectiveness
• D. It has no effect on lithium

Answer: (A)

Adequate sodium matters because lithium is handled by the kidneys in a way that mirrors sodium. In the proximal tubule, sodium and lithium compete for reabsorption. When sodium is low or a person is dehydrated, the kidneys reabsorb more sodium to conserve it, and lithium is reabsorbed along with it. That raises the lithium level in the blood and increases the risk of toxicity. If sodium intake is adequate, less lithium is reabsorbed and more is excreted, helping maintain lithium within a safe, therapeutic range. Keeping a consistent sodium intake and staying hydrated helps prevent fluctuations in lithium levels and toxicity.