Sodium is concentrated on the outside of your cells, in contrast with potassium, which exists predominantly inside your cells. The amount of sodium in the extracellular fluid helps determine the amount of water your body retains. If your sodium intake is high, your kidneys cut back on releasing water into your urine so you can balance out the excess sodium surrounding your cells. This results in an increased blood volume due to water retention. Symptoms include edema, or swelling, in various parts of your body.