Too much sodium in the bloodstream causes the body to retain extra water to dilute it. This can cause swelling of the blood vessels, which can cause them to harden over time. That hardening raises blood pressure and makes the heart work harder. When this has happened, reducing sodium intake will help reduce blood pressure by reducing the volume of fluid the heart has to circulate.

But if your blood vessels haven't hardened, there are other ways of helping to regulate your salt levels in addition to, or instead of, decreasing sodium intake. Drinking more liquids will help your kidneys process more sodium, and regular exercise will also help.

Good link though.