Potassium is an essential dietary mineral that is also known as an electrolyte. The term electrolyte refers to a substance that dissociates into ions (charged particles) in solution making it capable of conducting electricity. The normal functioning of our bodies depends on the tight regulation of potassium concentrations both inside and outside of cells.
Maintenance of membrane potential
Potassium is the principal positively charged ion (cation) in the fluid inside of cells, while sodium is the principal cation in the fluid outside of cells. Potassium concentrations are about 30 times higher inside than outside cells, while sodium concentrations are more than 10 times lower inside than outside cells. The concentration differences between potassium and sodium across cell membranes create an electrochemical gradient known as the membrane potential. A cell's membrane potential is maintained by ion pumps in the cell membrane, especially the sodium, potassium-ATPase pumps. These pumps use ATP (energy) to pump sodium out of the cell in exchange for potassium (diagram). Their activity has been estimated to account for 20%-40% of the resting energy expenditure in a typical adult. The large proportion of energy dedicated to maintaining sodium/potassium concentration gradients emphasizes the importance of this function in sustaining life. Tight control of cell membrane potential is critical for nerve impulse transmission, muscle contraction, and heart function.
Cofactor for enzymes
A limited number of enzymes require the presence of potassium for their activity. The activation of sodium, potassium-ATPase requires the presence of sodium and potassium. The presence of potassium is also required for the activity of pyruvate kinase, an important enzyme in carbohydrate metabolism.
An abnormally low plasma potassium concentration is referred to as hypokalemia. Hypokalemia is most commonly a result of excessive loss of potassium, e.g., from prolonged vomiting, the use of some diuretics, some forms of kidney disease, or disturbances of metabolism. The symptoms of hypokalemia are related to alterations in membrane potential and cellular metabolism. They include fatigue, muscle weakness and cramps, and intestinal paralysis, which may lead to bloating, constipation, and abdominal pain. Severe hypokalemia may result in muscular paralysis or abnormal heart rhythms (cardiac arrhythmias) that can be fatal.
Conditions that increase the risk of hypokalemia
* The use of potassium-wasting diuretics (e.g., thiazide diuretics or furosemide)
* Severe vomiting or diarrhea
* Overuse or abuse of laxatives
* Anorexia nervosa or bulimia
* Magnesium depletion
* Congestive heart failure (CHF)
In rare cases, habitual consumption of large amounts of black licorice has resulted in hypokalemia. Licorice contains a compound (glycyrrhizic acid) with similar physiologic effects to those of aldosterone, a hormone that increases urinary excretion of potassium. Low dietary intakes of potassium do not generally result in hypokalemia. However, recent research indicates that insufficient dietary potassium increases the risk of a number of chronic diseases (see Disease Prevention).
Adequate Intake (AI)
In 2004, the Food and Nutrition Board of the Institute of Medicine established an adequate intake level (AI) for potassium based on intake levels that have been found to lower blood pressure, reduce salt sensitivity, and minimize the risk of kidney stones.
The diets of western industrialized cultures are quite different from those of prehistoric cultures and the few remaining isolated primitive cultures. Among other differences, the daily intake of sodium chloride (salt) in western industrialized cultures is about 3 times higher than the daily intake of potassium on a molar basis, while salt intakes in primitive cultures are about 7 times lower than potassium intakes. The relative deficiency of dietary potassium in the modern diet may play a role in the pathology of some chronic diseases.
Several large epidemiological studies have suggested that increased potassium intake is associated with decreased risk of stroke. A prospective study of more than 43,000 men followed for 8 years found that men in the top quintile (1/5)of dietary potassium intake (averaging 4,300 mg/day) were only 62% as likely to have a stroke than those in the lowest quintile of potassium intake (averaging 2,400 mg/day). The inverse association was especially high in men with hypertension. However, a similar prospective study of more than 85,000 women followed for 14 years found a much more modest association between potassium intake and the risk of stroke. Another large study that followed more than 9,000 people for an average of 16 years found that potassium intake was inversely related to stroke only in black men and men with hypertension. However, black men and women reported significantly lower potassium intakes than white men and women (1,606 mg/day vs. 2,178 mg/day). More recent data from the same population indicates that those with potassium intakes higher than 1,352 mg/day were only 72% as likely to have a stroke as those with potassium intakes lower than 1,352 mg/day. Taken together, the epidemiological data suggest that a modest increase in fruit and vegetable intake (rich sources of dietary potassium), especially in those with hypertension and/or relatively low potassium intakes, could significantly reduce the risk of stroke.
Four cross-sectional studies have reported significant positive associations between dietary potassium intake and bone mineral density (BMD) in populations of premenopausal, perimenopausal, and postmenopausal women and elderly men. The average dietary potassium intakes of the study participants ranged from about 3,000 to 3,400 mg/day, while the highest potassium intakes exceeded 6,000 mg/day and the lowest intakes ranged from 1,400 to 1,600 mg/day. In all of these studies, BMD was also positively and significantly associated with fruit and vegetable intake. The only study to examine changes in BMD over time found that higher dietary potassium intakes (and fruit and vegetable intakes) were associated with significantly less decline in BMD at the hip in men, but not in women over a period of four years. Potassium-rich foods, such as fruits and vegetables are also rich in precursors to bicarbonate ions, which serve to buffer acids in the body. The modern western diet tends to be relatively low in sources of alkalai (fruits and vegetables) and high in sources of acid (fish, meats, cheeses). When the quantity of bicarbonate ions is insufficient to maintain normal pH, the body is capable of mobilizing alkaline calcium salts from bone in order to neutralize acids consumed in the diet and generated by metabolism (14). Increased consumption of fruits and vegetables reduces the net acid content of the diet and may preserve calcium in bones, which might otherwise be mobilized to maintain normal pH. Support for this theory was provided by a study of 18 postmenopausal women, which found that potassium bicarbonate supplementation decreased urinary acid and calcium excretion, while increasing biomarkers of bone formation and decreasing biomarkers of bone resorption.
Abnormally high urinary calcium (hypercalciuria) increases the risk of developing kidney stones. In individuals with a history of developing calcium-containing kidney stones, increased dietary acid load was significantly associated with increased urinary calcium excretion. Increasing dietary potassium (and alkalai) intake by increasing fruit and vegetable intake or by taking potassium bicarbonate supplements has been found to decrease urinary calcium excretion. Additionally, potassium deprivation has been found to increase urinary calcium excretion. A large prospective study of more than 45,000 men followed for 4 years found that men whose potassium intake averaged more than 4,042 mg/day were only half as likely to develop symptomatic kidney stones as men whose intake averaged less than 2,895 mg per day. A similar study that followed more than 90,000 women over a period of 12 years found that women in the highest quintile of potassium intake (averaging 3,458 mg/day) were only 65% as likely to develop symptomatic kidney stones as women in the lowest quintile of potassium intake (averaging 2,703 mg/day). In both these prospective studies, dietary potassium intake was derived almost entirely from potassium-rich foods, such as fruits and vegetables.
High blood pressure (hypertension)
A number of studies indicate that groups with relatively high dietary potassium intakes have lower blood pressures than comparable groups with relatively low potassium intakes. Data on more than 17,000 adults who participated in the Third National Health and Nutritional Examination Survey (NHANES III) indicated that higher dietary potassium intakes were associated with significantly lower blood pressures. The results of the Dietary Approaches to Stop Hypertension (DASH) trial provided further support for the beneficial effects of a potassium-rich diet on blood pressure. Compared to a control diet providing only 3.5 servings/day of fruits and vegetables and 1,700 mg/day of potassium, consumption of a diet that included 8.5 servings/day of fruits and vegetables and provided 4,100 mg/day of potassium lowered blood pressure by an average of 2.8/1.1 mm Hg (systolic BP/diastolic BP) in people with normal blood pressure and by an average of 7.2/2.8 mm Hg in people with hypertension. Increasing dietary calcium intake by 800 mg/day in the DASH trial lowered systolic and diastolic BP still further (see Calcium). More information about the DASH diet is available from the National Institutes of Health (NIH) Web site.
In 1997, a meta-analysis of 33 randomized controlled trials including 2,609 individuals assessed the effects of increased potassium intake, mostly in the form of potassium chloride (KCl) supplements, on blood pressure. Increased potassium intake (2,300-3,900 mg/day) resulted in slight but significant blood pressure reductions that averaged 1.8/1.0 mm Hg in people with normal blood pressure and 4.4/2.5 mm Hg in people with hypertension. Subgroup analysis indicated that the blood pressure-lowering effect of potassium was more pronounced in individuals with higher salt intakes and in trials where black individuals were a majority of the participants. A recent clinical trial in 150 Chinese men and women with borderline to mild hypertension found that moderate supplementation with 500 mg/day of potassium chloride for 12 weeks resulted in a significant 5 mm Hg reduction in systolic BP but not diastolic BP compared to placebo. Like many Western diets, the customary diet of this population was high in sodium and low in potassium.
The richest sources of potassium are fruits and vegetables. People who eat large amounts of fruits and vegetables have a high potassium intake (8-11 grams/day). A recent dietary survey in the U.S. indicated that the average dietary potassium intake is about 2,300 mg/day for adult women and 3,100 mg/day for adult men. The potassium content of some relatively potassium-rich foods is listed in milligrams (mg) in the table below. For more information on the nutrient content of foods you eat frequently, search the USDA food composition database.
Multivitamin/mineral supplements in the U.S. do not contain more than 99 mg of potassium per serving. Higher doses of supplemental potassium are generally prescribed to prevent and treat potassium depletion and hypokalemia. The use of more potent potassium supplements in potassium deficiency requires close monitoring of serum potassium concentrations. Potassium supplements are available as a number of different salts, including potassium chloride, citrate, gluconate, bicarbonate, aspartate and orotate. Because of the potential for serious side effects the decision to use a potent potassium supplement should be made in collaboration with one's health care provider (see Safety).
Abnormally elevated serum potassium concentrations are referred to as hyperkalemia. Hyperkalemia occurrs when potassium intake exceeds the capacity of the kidneys to eliminate it. Acute or chronic renal (kidney) failure, the use of potassium-sparing diuretics, and insufficient aldosterone secretion (hypoaldosteronism) may result in the accumulation of excess potassium due to decreased urinary potassium excretion. Oral doses greater than 18 grams taken at one time in individuals not accustomed to high intakes may lead to severe hyperkalemia, even in those with normal kidney function. Hyperkalemia may also result from a shift of intracellular potassium into the circulation, which may occur with the rupture of red blood cells (hemolysis) or tissue damage (e.g., trauma or severe burns). Symptoms of hyperkalemia may include tingling of the hands and feet, muscular weakness, and temporary paralysis. The most serious complication of hyperkalemia is the development of an abnormal heart rhythm (cardiac arrhythmia), which can lead to cardiac arrest. See Drug interactions for a discussion of the medications that increase the risk of hyperkalemia.
Adverse reactions to potassium supplements
Gastrointestinal symptoms are the most common side effects of potassium supplements, including nausea, vomiting, abdominal discomfort, and diarrhea. Intestinal ulceration has been reported after the use of enteric-coated potassium chloride tablets. Taking potassium with meals or taking a microencapsulated form of potassium may reduce gastrointestinal side effects. The most serious adverse reaction to potassium supplementation is hyperkalemia (see Toxicity). Individuals with abnormal kidney function and those on potassium-sparing medications (see Drug interactions) should be monitored closely to prevent hyperkalemia.
Linus Pauling Institute Recommendation
There is considerable evidence that a diet supplying at least 4.7 grams/day of potassium is associated with decreased risk of stroke, hypertension, osteoporosis, and kidney stones. Fruits and vegetables are among the richest sources of dietary potassium, and a large body of evidence supports the association of increased fruit and vegetable intakes with reduced risk of chronic disease. Consequently, the Linus Pauling Institute recommends increasing potassium intake to at least 4.7 grams/day by increasing consumption of potassium-rich foods, especially fruits, vegetables, and nuts.
Adults over the age of 65
A diet supplying at least 4.7 grams/day of potassium is also appropriate for healthy older adults since such diets are associated with decreased risk of stroke, hypertension, osteoporosis, and kidney stones. This recommendation does not apply to individuals who have been advised to limit potassium consumption by a health care professional.