February 2008

The Pressure’s On: Increasing Potassium for Heart Health
By Christen C. Cooper, MS, RD
Today’s Dietitian
Vol. 10 No. 2 P. 34

The results are in: This oft-neglected mineral can help thwart sodium’s harmful effects and benefit the overall health of the body’s most vital muscle.

Potassium. Compared with other micronutrients, it gets little fanfare. It has no slogan or clever jingle. It has no lobbyists in Washington. Let’s face it—when we think of blood pressure, we think of sodium. When we think of bone health, we think of calcium. We think of potassium as crucial for certain people—athletes, seniors, and renal patients—but of little consequence to the typical healthy individual.

But rewind, if you will, to basic biochemistry. You may remember that potassium is the major intracellular cation in the human body. More than one third of our energy is expended in pumping potassium and its ionic counterpart, sodium, into and out of cells.1 This strong, silent mineral helps conduct nerve impulses, contract muscles, and maintain optimal body pH, not to mention support bone and kidney health. The truth is, potassium is crucial for everyone, and disrupting optimal body levels of it can be dangerous—even lethal.

For years, sodium bore the brunt of the dietary blame for heart disease. And there’s no doubt about it—Americans consume too much salt. A full 100% of American men and women get well above the adequate intake of 1,500 milligrams per day of sodium chloride, and more than 95% of American men and 75% of American women regularly consume more than the upper intake level of 2,300 milligrams per day.2 According to the Dietary Guidelines Advisory Committee and a consensus of government health authorities, there is solid evidence for the “direct and progressive” relationship between sodium intake and blood pressure.2,3

On the other hand, Americans come up short on potassium in the diet. A severe potassium deficiency, or hypokalemia—rare in healthy individuals—is characterized by serum potassium of less than 3.5 millimoles per liter. Hypokalemia can result in serious consequences such as cardiac arrhythmias, muscle weakness, and glucose intolerance. However, research shows that a great number of Americans live day to day with a more moderate potassium deficit, which poses longer term health threats.4 This condition appears to result from the dearth of potassium in the typical American diet, which has become heavy in processed, high-sodium foods and light in potassium-rich fruits and vegetables.

Data from the National Health and Nutrition Examination Survey follow-up study support the notion of a potassium deficiency. American men get approximately 2.9 to 3.2 grams per day and women roughly 2.1 to 2.3 grams per day.4 And research supports reason for concern. For more than 40 years, scientists have hypothesized that potassium may have a positive effect on cardiovascular health. In recent years, experimental studies have demonstrated that a moderate potassium deficiency can lead to hypertension and related cardiovascular events, as well as an increased risk for bone loss and kidney stones. A recent article in The New England Journal of Medicine states that “abundant evidence indicates that a potassium deficit has a critical role in hypertension and its cardiovascular sequelae.”5

American Heart Month reminds us that in 2007, a whopping 1.2 million Americans will have had a coronary attack, and 700,000 will have suffered a stroke.6 Numbers like these require us to rethink the ways that we fight heart disease. No single factor is a cure-all, but the best approach is to combine the best solutions we know of—for example, lowering salt, increasing potassium, and exercising more—to hold onto heart health for as long as possible.

Paleolithic Potassium
Dietitians may think that because Americans eat so much, they must get enough of everything, including potassium. In fact, most people probably do get too much. After all, the body is able to absorb a substantial 80% to 90% of the potassium ingested.7 However, there are some reasons our bodies still want for this valuable mineral.

Studies suggest that a high sodium intake increases urinary potassium excretion. But this may not be the biggest issue. Scientists believe that our problem with potassium may date back to the Stone Age. Paleolithic hunter-gatherers ate a plant-based diet high in potassium and low in sodium, with a potassium to sodium ratio of 3 to 1. Hence, the human kidney evolved to keep the body’s electrolytes in balance by readily excreting potassium and conserving sodium.

The modern Western diet, with an electrolyte ratio of sodium to potassium of approximately 4 to 1, has essentially the opposite proportions of the early human diet.5 This is because whole foods make up a smaller part of the modern diet than processed foods, which are normally salt laden and often stripped of naturally occurring nutrients such as potassium.

Observational studies, including INTERSALT (International Study of Salt and Blood Pressure), which involved 10,079 subjects from 32 nations, found that the dietary sodium to potassium ratio had a stronger association with blood pressure than sodium or potassium alone. In countries such as Japan, where sodium intake is high yet people consume traditional diets of largely whole foods, rates of high blood pressure remain, on average, lower than those of Western nations.3,5,8

Potassium: Sodium Proportions
Sodium and potassium can be at odds with each other. But they also continually work together at the cellular level to control cellular volume, pH, and membrane potential. The sodium-potassium exchange pump, or sodium pump, which provides energy for a number of critical cellular functions, triggers a cascade of events leading to the constriction or relaxation of blood vessels. It does this based on the concentrations of electrolytes in the intracellular and extracellular space.

In a potassium deficit scenario, sodium enters cells to maintain cellular volume. Then water follows sodium into the cells, increasing pressure on artery walls. Over time, this extra pressure leads to stiffness and, in some people, high blood pressure. As explained in a recent study, sodium depolarizes cellular membranes, leading to vasoconstriction, the kind characteristic of primary hypertension.5 On the other hand, ample dietary potassium causes sodium pump stimulation and endothelial cell hyperpolarization. This ultimately relaxes blood vessels, allowing blood to flow freely and keeping blood pressure at normal levels.

Potassium’s Partners
The full extent of the process by which potassium may help control blood pressure has not been elucidated. Some studies suggest that the antipressor effects of dietary potassium may come from its natriuretic effects since potassium acts on the renal tubule to increase salt excretion.4 Other studies suggest that it is the conjugate anion occurring with potassium, whether citrate or chloride, that confers benefits.

The favored conjugate anion is potassium citrate, a bicarbonate-generating form of potassium found in fruits and vegetables. Studies suggest that this form promotes lower blood pressure because it produces a larger cellular entry when exchanged for sodium in cells.5,7 Unlike potassium chloride, which is the form of potassium found in meats and selected grains, potassium citrate appears to have an alkalinizing effect on the body. Some researchers believe that the bicarbonate-generating citrate form may help prevent a low-grade metabolic acidosis resulting from a diet heavy in animal foods. Even a low-grade state of acidosis can be detrimental because in order to buffer the acidity, the body chips calcium away from bone. This leads to hypercalciuria and hypocitraturia, which can express themselves as bone demineralization and kidney stones.7

Of course, the benefits of a particular anion are hard to separate from plant foods’ numerous other heart-healthy substances, including fiber, antioxidants, and phytochemicals. But again, in the Dietary Approaches to Stop Hypertension (DASH) diet, we see evidence that fruit and vegetable intake correlates with better heart health, including lower blood pressure. The DASH trial compared a “typical” American diet with a diet high in fruits and vegetables (eight to 10 servings) and also with a diet rich in plant foods and low-fat dairy. All three diets provided approximately 140 millimoles of sodium chloride per day. Both experimental diets led to reductions in blood pressure, with the greater drop observed in subjects assigned to the dairy-inclusive diet.5,7

In a second DASH study, researchers decided to test different sodium intake levels—and therefore the impact of sodium specifically—on each of the three diets. Again, there was a dose-dependent hypotensive effect, with the greatest blood pressure drop occurring in the DASH diet group with the greatest sodium chloride restriction.

But the hypotensive effects attributable to the sodium level were most pronounced in the control group. In other words, in the group for which potassium intake was lowest (50 millimoles per day), the salt restriction had the greatest impact. One review states: “It seems likely that the hypotensive effect of the DASH diet is to a considerable extent determined by its relatively high potassium intake, and possibly to some extent by a greater renal calcium retention thereby induced.”7

Potassium in a Pill
Additional benefits may come from further supplementing a potassium-rich diet, as shown in a handful of studies on potassium supplementation. These works show that supplementing the DASH diet with potassium citrate can further decrease blood pressure and the excretion of calcium in the urine.7 Supplemental potassium bicarbonate blunted the effects of salt on salt-sensitive hypertensive and nonhypertensive individuals in a number of studies. Salt sensitivity refers to the pressor effect of salt on blood pressure. In one trial, increasing potassium intake to 4.7 grams per day had a particularly notable positive effect on salt sensitivity in nonhypertensive African Americans.2,7 This is important because suppression of salt sensitivity is thought to delay or prevent hypertension. It is also important because African Americans tend to consume less potassium and are more likely to have salt sensitivity.4

Recommendations
The Institute of Medicine (IOM) set the adequate intake for potassium at 4.7 grams per day for healthy adults, a level that nine or 10 servings of fruits and vegetables provide.1 The IOM recommendation is supported by evidence that 4.7 grams of potassium per day should lower blood pressure, help counter the effects of sodium chloride on blood pressure, and reduce the risk of kidney stones and bone loss.4

The 2005 Dietary Guidelines Advisory Committee followed suit when it set the new, controversial fruit and vegetable goal at 41/2 cups per day. (This, by the way, is roughly equal to the IOM’s nine to 10 servings.) Like the IOM report, the Dietary Guidelines Advisory Committee Report clearly states that a diet rich in potassium can help fight high blood pressure, lessen the effects of salt on blood pressure, and help prevent kidney stones and bone loss.2

Tips for Advising Clients
For many people, increasing potassium may be a more useful heart health strategy than simply trying to reduce sodium. After all, it’s generally easier to get Americans to eat more, not less. So try to suggest some gastronomic experimentation to add not only potassium but also interesting elements to winter foods and brighten up the season.

• Who says meat and potatoes people can’t be heart healthy? There’s nothing that matches a potato when it comes to potassium. So roast it, bake it, mash it—just don’t deep fry it—and you’ll have a heart-healthy dish. By the way, beef’s also a good source, but keep it lean.

• Starchy winter foods such as sweet potatoes and acorn squash are bursting with potassium and can be roasted or tossed into soups and stews for a warm, savory, and potassium-rich accent. (Roasted veggies can add so much natural flavor that the dishes they join need less salt, another heart-healthy benefit.)

• International cuisines can offer potassium-rich inspirations. Toss chickpeas into salads; add lentils to soups or as a side. With a few spices, these legumes lend themselves to a number of Indian and Middle Eastern dishes.

• There are numerous fish, including tuna, halibut, salmon, and flounder, that are potassium rich. Beef, chicken, and pork also contain ample potassium.

• Suggest adding fruits such as oranges (since citrus is generally available and tastes good in winter) and dried fruits such as raisins into salads for variety in taste and color.

• What better classic potassium-rich food can one find than a banana? Suggest a smoothie made with a banana, a cup of frozen berries, a teaspoon of honey, and a tablespoon of wheat germ in the morning for breakfast, or a banana split made with low-fat or nonfat frozen yogurt with a sprinkling of peanuts or almonds and raisins for dessert.

Advise clients who may want to try potassium supplements to proceed with caution and seek a physician’s advice before taking it or any supplement: Although potassium is readily excreted by the body, some forms of potassium in excess can cause disruption of heart rhythms and other heart problems. As always, clients with renal problems should limit potassium and have serum potassium carefully monitored by their physician. For most people, unless their doctors advise otherwise, it’s better to increase potassium through potassium-rich foods.

Cultural awareness can also be a boon for advising people on how to boost potassium. For many newcomers to the United States, the diet eaten prior to arrival was richer in fruits and vegetables than the diet consumed here. We know the challenges of finding affordable fruits and vegetables in many places across the country. Encourage visits to farmers’ markets and farm stands, where quality produce can usually be found at affordable prices and where human interaction and an exchange of information with sellers can make for a unique, informative, and enjoyable experience.

— Christen C. Cooper, MS, RD, is a Pleasantville, N.Y.-based freelance health and nutrition writer. She has worked in healthcare consulting in Latin America and the United States and holds a master’s degree in nutrition education from Teachers College, Columbia University.

References

1. Schardt D. Potassium: Bones, stones, & strokes on the line. Nutrition Action Healthletter. 2004;31(10):8-9.

2. U.S. Department of Health and Human Services. Part D, Section 7: Fluid and Electrolytes. The Report of the Dietary Guidelines Advisory Committee on Dietary Guidelines for Americans 2005. Available here.

3. Alderman MH. Presidential Address: 21st Scientific Meeting of the International Society of Hypertension: Dietary sodium and cardiovascular disease: The ‘J’-shaped relation. J Hypertens. 2007;25(5):903-907.

4. Panel on Dietary Reference Intakes for Electrolytes and Water, Standing Committee on the Scientific Evaluation of Dietary Reference Intakes. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. Washington, DC: National Academics Press; 2004.

5. Adrogué HJ, Madias NE. Sodium and potassium in the pathogenesis of hypertension. N Eng J Med. 2007;356(19):1966-1978.

6. American Heart Association,American Stroke Association. Heart Disease and Stroke Statistics: 2007 Update At-a-Glance. Available here.

7. Morris RC Jr, Schmidlin O, Frassetto LA, et al. Relationship and interaction between sodium and potassium. J Am Coll Nutr. 2006;25(3 Suppl):262S-270S.

8. Khaw KT, Bingham S, Welch A, et al. Blood pressure and urinary sodium in men and women: The Norfolk Cohort of the European Prospective Investigation into Cancer (EPIC-Norfolk). Am J Clin Nutr. 2004;80(5):1397-1403.