A nurse is teaching a client who has a new prescription for lithium to treat bipolar disorder. The nurse should instruct the client to ensure an adequate intake of which of the following dietary elements?

The correct answer is A: Sodium. Lithium is a mood stabilizer commonly used to treat bipolar disorder. Sodium intake is crucial while on lithium therapy because it competes with lithium for reabsorption in the kidneys. Adequate sodium levels help maintain a stable lithium level in the blood, preventing lithium toxicity. Potassium, Vitamin C, and Vitamin K do not directly interact with lithium metabolism; therefore, they are not essential to monitor specifically for lithium therapy. Sodium is the only dietary element that directly impacts the therapeutic effectiveness and safety of lithium.