Rather than estimating dietary intake, researchers measured actual levels of sodium and potassium in the urine of 2,275 subjects with prehypertension (diastolic blood pressure between 80 and 89) and followed them for 10 to 15 years.
Again, higher sodium seemed to increase the risk of heart attack and stroke, and potassium seemed to have the opposite effect. But the only association that passed muster statistically was the balance between sodium and potassium. "The size of the effect was very similar to the CDC study," noted study coauthor Nancy Cook, a researcher in preventative medicine at Brigham and Women's Hospital in Boston.
Focusing on the ratio between sodium and potassium makes biological sense because the minerals are known to have opposite effects on blood pressure, Kuklina said. Sodium generally increases blood pressure and signals the body to retain fluids. Potassium, however, relaxes blood vessels, lowers blood pressure and helps rid the body of excess fluids.
The U.S. dietary guidelines recommend limiting sodium intake to 2,300 milligrams per day and even lower — 1,500 mg — for those 51 and older and people of any age who are African American or have high blood pressure, kidney disease or diabetes. (The American Heart Assn. recently switched to a target of 1,500 mg per day for everyone.)
The average daily intake of sodium by Americans is much higher than that — more than 3,400 mg per day, according to CDC estimates.
Recommended potassium intake is 4,700 mg per day, but average U.S. intake is in the range of only 2,000-2,500 mg per day, Cook said.
The best potassium sources are fruits and vegetables such as potatoes, bananas, grapes, carrots, greens and citrus fruits.
- One banana – 400 mg potassium
- One potato – 900 mg potassium
- One cup spinach – 950 mg potassium
- 1/2 cup raisins – 600 mg potassium
- 8 ounces (one cup) orange juice – 500 mg potassium
For people with hypertension, an eating plan called DASH (Dietary Approaches to Stop Hypertension) may be useful for lowering blood pressure. The DASH diet is higher in potassium, magnesium and calcium and lower in total fat, saturated fat added sugars and sodium than what is usually in the typical American diet. The DASH diet is also rich in fruits, vegetables, low-fat and nonfat dairy and includes whole grains, nuts/beans/seeds, lean meats, fish, poultry, and heart-healthy fats.