Sodium is found in your blood and in inter-cellular fluids. It plays a very important role in maintaining a balance between various bodily fluids. Bags under the eyes, as well as edema of the legs, is a sign that there is too much salt in your system (excess salt, as you probably know, can cause hypertension). Reducing your salt intake for a few weeks should help solve the problem. Other possible causes of bags under the eyes are a lack of sleep and prolonged stress.