Regulation of Potassium Concentrations

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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.

 

Function

 

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 .

 

Deficiency

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)

Alcoholism

Severe vomiting or diarrhea

Overuse or abuse of laxatives

Anorexia nervosa or bulimia

Magnesium depletion

 

 

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

 

Disease Prevention

 

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

(6).

 

The relative deficiency of dietary potassium in the modern diet may

play a role in the pathology of some chronic diseases.

 

Stroke

 

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) (7). 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 (8).

 

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 (9).

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 (10).

 

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.

 

Osteoporosis

 

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 (11-13). 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 (13).

 

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 (15).

 

Kidney stones

 

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 (16).

 

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 (17, 18). 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 (19).

 

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) (20).

 

In both these prospective studies, dietary potassium intake was

derived almost entirely from potassium-rich foods, such as fruits

and vegetables.

 

Disease Treatment

 

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 (21). 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 (22).

 

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 (23). 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 (24).

 

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

(25). Like many Western diets, the customary diet of this population

was high in sodium and low in potassium.

 

Sources

 

Food sources

 

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) (4). 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 (22).

 

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.

 

Food Serving Potassium (mg)

 

Banana 1 medium 467

Potato, baked with skin 1 medium 721

Prune juice 6 fluid ounces 530

Prunes, dried 1/2 cup 633

Orange juice 6 fluid ounces 354

Orange 1 medium 237

Tomato juice 6 fluid ounces 400

Tomato 1 medium 273

Raisins 1/2 cup 598

Raisin bran cereal 1 ounce 437

Artichoke, cooked 1 medium 425

Lima beans, cooked 1/2 cup 478

Acorn squash, cooked 1/2 cup (cubes) 448

Spinach, cooked 1/2 cup 419

Sunflower seeds 1 ounce 241

Almonds 1 ounce 211

Molasses 1 tablespoon 293

 

 

 

Supplements

 

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 (26). 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).

 

Safety

 

Toxicity (excess)

 

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 (4). 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 (27). 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 (5, 26).

 

Drug interactions

 

The following classes of medication are known to increase the risk

of hyperkalemia (elevated serum potassium) (27):

 

Medications Associated with Hyperkalemia

Medication Family

Specific medications

 

Potassium-sparing agents Spironolactone, triamterene, amiloride

Angiotensin converting enzyme (ACE) inhibitors Captopril,

enalapril, fosinopril

Nonsteroidal anti-inflammatory agents (NSAID) Indomethacin,

ibuprofen, ketorolac

Anti-infective agents Trimethoprim-sulfamethoxazole, pentamidine

Anticoagulant Heparin

Cardiac glycoside Digitalis

Anti-hypertensive agents Beta-blockers, alpha- and beta-blockers

Angiotensin receptor blockers Losartan, valsartan, irbesartan,

candesartan

 

 

 

The following medications are known to increase the risk of

hypokalemia (low serum potassium) (5):

 

Medications Associated with Hypokalemia

Medication family Specific medications

Beta-adrenergic agonists Epinephrine

Decongestants Psuedoephedrine, phyenylpropanolamine

Bronchodilators Albuterol, terbutaline, pirbuterol, isoetharine,

fenoterol, ephedrine, isoporterenol, metaproternenol, theophylline

Tocolytic (labor suppressing) agents Ritodrine, nylidrin

Diuretics Acetazolamide, thiazides, chlorthalidone, indapamide,

metolazone, quinethazone, bumetanide, ethycrinic acid, furosemide,

torsemide

Mineralocorticoids Fludrocortisone

Substances with mineralocorticoid effects Licorice, carbenoxolone,

gossypol

High-dose glucocorticoids

High-dose antibiotics Penicillin, nafcillin, carbenicillin

 

Other

Caffeine, phenopthalein, sodium polystyrene sulfonate

 

 

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 (28,29). Consequently, the Linus Pauling Institute

recommends increasing potassium intake to at least 4.7 grams/day by

increasing consumption of potassium-rich foods (see Sources),

especially fruits, vegetables, and nuts.

 

 

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.