Sodium, found outside cells, and potassium, found mainly inside cells, are minerals that work together to maintain fluid balance in the body. They are also involved in the regulation of muscle contractions and nerve transmissions and play an important role in controlling blood pressure.
Although sodium occurs naturally in foods, people consume most of their dietary sodium from salt added to foods in processing, in cooking, or at the table and from sodium-containing compounds in food—for example, sodium bicarbonate (baking soda) and monosodium glutamate (MSG). Keep in mind that sodium and salt are not the same thing. Only 40 percent of table salt (sodium chloride) is sodium; the other 60 percent is chloride.
Sodium, potassium and hypertension
Most Americans consume too much sodium—more than 4,000 mg a day, which is more than twice the recommended amount—and too little potassium. This sodium-potassium imbalance increases the risk of high blood pressure, which can lead to heart attack and stroke. All Americans need to lower their sodium intake to prevent and control high blood pressure.
Hypertension is defined as a blood pressure of 140/90 mm Hg or higher—a systolic blood pressure of 140 mm Hg or higher and/or a diastolic blood pressure of 90 mm Hg or higher. Having prehypertension (a systolic blood pressure between 120 and 139 mm Hg and/or a diastolic blood pressure between 80 and 89 mm Hg) also puts you at risk for heart attacks and strokes. Some studies estimate that if everyone stopped adding salt to food (which accounts for about a third of the sodium in most diets), the number of people who need blood pressure medication would be cut in half.
Your diet plays an important role in keeping your blood pressure at a healthy level. The DASH (Dietary Approaches to Stop Hypertension) trial proved that a healthy diet could reduce blood pressure in people with and without hypertension. The diet used in the eight-week study consisted of eight to 10 servings of fruits and vegetables and two to three servings of low-fat dairy products each day. The diet also encouraged people to eat plant sources of protein (such as soy) at least once or twice a week.
By the end of the trial, the DASH diet reduced blood pressure by an average of 5.5/3 mm Hg in people without hypertension compared with the control diet (which was the typical American diet: low in fruits and vegetables and high in fat). Some of the most impressive results with the DASH diet were in people with hypertension: They lowered their blood pressure by 11.4/5.5 mm Hg, similar to the amount that a single blood pressure medication typically lowers blood pressure.
Results from a subsequent study, the DASH-Sodium trial, indicated that, in people without hypertension, combining the DASH diet with a reduced sodium intake lowered blood pressure even more than the original DASH diet.
The participants followed a diet that combined the DASH diet with one of three levels of sodium intake (3,300 mg, 2,400 mg or 1,500 mg a day). At the end of the study, participants without high blood pressure who consumed the DASH diet with the least sodium had systolic blood pressure levels 7 mm Hg lower than those of people who ate the typical American diet with a high sodium level.
In people with hypertension, the low-sodium DASH diet also lowered systolic blood pressure by 12 mm Hg more than in those who ate a typical American diet. In addition, eating a DASH-style diet saves lives over time, according to research based on 24 years of data on 88,000 women in the Nurses’ Health Study. A 2008 analysis found that participants who ate a DASH-like diet were 24 percent less likely to develop fatal or nonfatal coronary heart disease and 18 percent less likely to have a stroke than those who didn’t.
A large part of the success of the DASH-Sodium diet may be its high potassium content—about 4,400 mg daily (roughly the amount in 11 bananas). Research indicates that potassium lowers blood pressure by relaxing arteries. Potassium also dampens the rise in blood pressure that occurs with excessive sodium consumption, and it reduces the risk of kidney stones and decreases bone loss.
Sodium and other disorders
There are several other reasons that you should reduce sodium in your diet. A high-sodium diet can increase the loss of calcium in the urine, which in turn triggers the removal of calcium from bones. An intake of 3,000 mg or more of sodium daily can also increase the risk of stomach cancer, because sodium irritates the lining of the stomach, especially in people who have had ulcers.
Finally, excess sodium intake contributes to kidney disease because of its blood pressure-raising effect. Chronic high blood pressure damages organs by injuring the blood vessels that supply them, and the kidneys are particularly vulnerable to such damage.