If you have a family history of stroke or have had a stroke yourself, if you have high blood pressure or need to prevent it, and especially if you take diuretics to control high blood pressure, you’ll want to learn all you can about potassium. It could save your life. Potassium is one of those essential nutrients that’s found pretty much everywhere in your body. It’s especially concentrated inside cells. There, it helps maintain the proper balance of fluid and other electrolytes such as sodium and chloride, which allow a cell to act like a tiny battery with its own electrical charge. The ability to generate an electrical charge is what lets cells do their work—if they’re in muscles, to contract and relax, if they’re in nerves, to fire off signals, and if they’re in glands, to secrete hormones.
The electrical charge also lets cells move things in and out through their membranes, activate enzymes involved in chemical reactions, and maintain proper pH (acid-base balance) within the cell walls. "Potassium plays a very basic and vital role in practically all aspects of cell activity," says Louis Tobian, M.D., professor of medicine at the University of Minnesota Medical School in Minneapolis.
Potassium does a balancing act with sodium, which is one reason that it’s so vital in maintaining proper blood pressure, Dr. Tobian explains. It works with sodium but also helps to keep it in check. During nerve transmission and muscle contraction, potassium and sodium briefly trade places across the cell membrane. Then they swap again, returning to their original positions ready for action.
Proper Pressure
There’s growing evidence that the more potassium you get in your diet, the less likely you are to develop high blood pressure. One reason for this probably has to do with potassium’s interaction with sodium, says David B. Young, Ph.D., professor of physiology and biophysics at the University of Mississippi Medical Center in Jackson. "The more potassium you get in your diet, the greater your ability to excrete sodium in your urine," he says.
Think of sodium as a water magnet. "When you excrete sodium, you also excrete water," says Dr. Young. "Excreting water reduces your blood volume, which in turn reduces your blood pressure. Thus, potassium achieves the same goal as a diuretic."
Potassium also inhibits the release of a hormone called renin from the kidneys. Renin activates another hormone, called angiotensin, which throws the switch on a kind of internal suction pump. When angioten-sin is activated, your blood vessels constrict and your kidneys start to retain sodium. Both of these actions bump up blood pressure. "Having low renin levels is good in terms of lowering blood pressure," Dr. Young says.
Some popular blood pressure medications such as captopril (Capoten) and enalapril maleate (Vasotec) work along similar lines by interfering directly with angiotensin. "Possibly, you could use potassium to get some of the same effects that these drugs provide," Dr. Young says. In fact, that’s the approach that some doctors take.
SUPPLEMENTSNAPSHOT
| Potassium May help: High blood pressure, stroke, leg cramps, and heart arrhythmia. Daily Value: 3,500 milligrams. Who’s at risk for deficiency: People taking non-potassium-sparing diuretics such as furosemide (Lasix), digitalis, or steroids; those who don’t eat fruits or vegetables, are heavy drinkers, have prolonged vomiting or diarrhea, overuse laxatives, or have eating disorders. Good food sources: Baked potatoes, spinach (raw, microwaved, or steamed for highest potassium content), dried apricots, dried prunes, Adzuki beans, avocados, watermelon, acorn squash, and bananas. Cautions and possible side effects: Appears to be safe at any amount in foods, even up to 11,000 milligrams a day, but do not get more than 5,000 milligrams a day from food and supplements without medical supervision. Large doses of supplements are available only by prescription; do not take without medical supervision. Excessive potassium can upset the balance of other minerals in the body and cause potentially fatal heart and kidney problems. |
Independent of its effect on blood pressure, high potassium intake also seems to have a protective effect on the kidneys, Dr. Young says. In animal studies, a high-potassium diet has been shown to help prevent thickening of the small arteries that feed blood to this pair of vital, blood-cleaning, urine-producing organs. Potassium also offers promise as a kidney-guarding mineral.
Keeping the Beat
A normal heartbeat may seem simple, but it’s a highly coordinated event, directed by the sequential firing of nerves that signal each chamber of the heart. When all goes well, the lower chambers and the upper chambers work in sequence, pumping blood to the lungs and the rest of the body.
When things go awry, the nerve signals may be delayed, or the nerves may fire more often than necessary. The chambers may not pump in proper sequence. The end result is that the heart pumps blood less efficiently. In fact, instead of pumping, it may go into a kind of quivery state, or arrhythmia, called fibrillation, which can be fatal if it’s not quickly corrected.
You need potassium for the muscles of the heart to stay strong, Dr. Young says. Even moderate potassium depletion weakens the heart muscle. Most people whose hearts are affected by low potassium already have some sort of heart damage, such as an enlarged heart or damage to the heart muscle from a heart attack. Then, if their potassium levels decrease, their risk for arrhythmia rises. That’s why most heart doctors monitor their patients’ blood levels of potassium.
Stop a Stroke
Because they can maintain low blood pressure and help your heart beat normally (which reduces your chances of developing blood clots), a potassium-rich diet and possibly even supplements have the potential to reduce your chance of having a stroke. In a study from the Harvard School of Public Health, doctors analyzed data from food questionnaires completed by nearly 44,000 healthy men ages 45 to 75. The conclusions of the study were based on two groups. Men in the high-potassium group consumed nine servings of fruits and vegetables a day. Men with diets that were lower in potassium ate only four servings of fruits and vegetables a day.
During the eight years of follow-up, doctors found that men in the first group had a 38 percent lower risk of stroke than men in the low-potassium group. Remarkably, the greatest benefit was seen among men who had a history of high blood pressure and were taking potassium supplements along with diuretics. Their risk was slashed by a whopping 64 percent.
Even if you can’t seem to get your blood pressure down all that much, potassium still offers protection, Dr. Young says. In the arteries, for instance, it helps stop the buildup of cholesterol-laden plaque. "We believe it does this by interfering somehow with the action of certain immune cells, called macrophages, that attack LDL in the blood vessel wall," Dr. Young says.
Potassium also decreases the sensitivity of platelets—the parts of the blood that clot—to things that activate them and make them sticky. It also prevents the overgrowth of smooth muscle cells in blood vessels. This is important because thickened and stiffened blood vessels are more prone to blockage. "In several types of animals, we know that if we give extra potassium, we can prevent lesions in the arteries, and we can prevent blockages that occur after arteries have been reopened with a procedure such as balloon angioplasty," Dr. Young says.
Potato Chips versus Oranges
If you were to have a severe case of potassium deficiency, you might experience symptoms of muscle weakness, confusion, and heart irregularities. Most of us will never have that problem, however, because our bodies carefully regulate potassium levels.
"People don’t develop severe potassium deficiencies unless they have some sort of endocrine or kidney problem, and then they are pretty sick for a number of reasons," Dr. Young says. While some diuretic drugs can seriously deplete the body of potassium, doctors monitor blood levels of potassium in people taking diuretics and supply extra potassium if necessary.
It’s likely that a fair number of people in the United States are on the same kind of low-potassium, high-sodium diet that can cause high blood pressure and heart disease in animals, Dr. Tobian says. Many people just don’t get their share of potassium-rich fruits and vegetables, and because of safety concerns, potassium isn’t found in adequate amounts in multi vitamin/mineral supplements.
While potassium from foods has not been associated with any ill effects, the same can’t be said for potassium supplements. "You can kill yourself if you take too much potassium," Dr. Tobian says.
Prescription supplements do offer more potassium, but amounts need to be carefully monitored with blood tests, Dr. Tobian says. People might need prescription potassium supplements if they are taking diuretics that deplete potassium. For his patients with high blood pressure, those who have had strokes, or those who have family histories of stroke, Dr. Tobian combines a potassium-rich diet with supplements if necessary.
