http://www.nhlbi.nih.gov/health/public/heart/hbp/dash/new_dash.pdf

What Is the DASH Eating Plan?
Blood pressure can be unhealthy even if it stays only slightly above the normal level of less than 120/80 mmHg. The higher blood pressure rises above normal, the greater the health risk.
In the past, researchers tried to find clues about what in the diet affects blood pressure by testing various single nutrients, such as calcium and magnesium. These studies were done mostly with dietary supplements and their findings were not conclusive. Then, scientists supported by the National Heart, Lung, and Blood Institute (NHLBI)conducted two key studies. The first was called “DASH,” and it tested nutrients as they occur together in food.

Its findings showed that blood pressures were reduced with an
eating plan that is low in saturated fat, cholesterol, and total fat, and that emphasizes fruits, vegetables, and low fat dairy foods. This eating plan—known as the DASH eating plan—also includes whole grain products, fish, poultry, and nuts. It is reduced in red meat, sweets, and sugar-containing beverages. It is rich in magnesium, potassium, and calcium, as well as protein and fiber.

The DASH study involved 459 adults with systolic blood pressures of less than
160 mmHg and diastolic pressures of 80–95 mmHg. About 27 percent of the
participants had hypertension. About 50 percent were women and 60 percent were
African Americans.

The DASH diet can lower blood pressure by 8-14 mm Hg ( points )
Whereas lowering sodium intake can lower blood pressure by 2-8 mm Hg.

The natural ways to lower blood pressure are reviewed in the following article:

Primary Prevention of Hypertension JAMA. 2002;288:1882-1888

6 approaches with proven efficacy for prevention of hypertension:
1.engage in moderate physical activity( 4-9mmHg)
2. maintain normal body weight; ( 5-10 mmHg)
3. limit alcohol consumption ( 2-4 mmHg )
4. reduce sodium intake; ( 2 - 8 mm Hg )
5.maintain adequate intake of potassium; and
6.consume a diet rich in fruits, vegetables, and low-fat dairy products and reduced in saturated and total fat
DASH ( 8 - 14 mm Hg )