Too much sodium in your system causes your body to retain (hold onto) water. This puts an extra burden on your heart and blood vessels. In some people, this may lead to high blood pressure or may raise blood pressure. Having less sodium in your diet may help you lower or avoid high blood pressure. People with high blood pressure are more likely to develop heart disease or have a stroke.
Most people eat too much sodium, often without knowing it. One teaspoon of salt contains about 2,300 mg of sodium. Your body only needs 200 mg of sodium per day. The average American eats about 3,000 to 3,600 mg of sodium per day. The American Heart Association recommends that Americans reduce the amount of sodium in their diet to less than 1,500 mg per day. Your doctor may tell you to cut salt out completely. Talk with him or her about the right amount of salt for your diet.
— Source: American Heart Association