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?

A. Sodium intake is crucial for clients on lithium, as low sodium levels can lead to lithium toxicity; therefore, maintaining a normal sodium level is important. B. While potassium is important for general health, it does not specifically impact lithium levels. C. Vitamin C is beneficial for overall health but does not have a direct relationship with lithium therapy. D. Vitamin K is related to blood clotting and does not have a significant interaction with lithium treatment or its efficacy.