Marathon runners are encouraged to stop at water stations along the course to stay hydrated. However, occasionally a runner drinks too much water and suffers from hyponatremia, or "water intoxication". While water itself is not toxic, drinking too much can upset ion balance in the extracellular space.

Based on what you know about ions and nerve signaling, the levels of which important ion are most likely to be disrupted in hyponatremia?

A. hydrogen

B. potassium

C. calcium

D. sodium

E. oxygen