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TABLE 1 Dietary Reference Intakes for Potassium by Life Stage Group DRI values (g/day) AIa ULb Life stage groupc 0 through 6 mo 0.4 7 through 12 mo 0.7 1 through 3 y 3.0 4 through 8 y 3.8 9 through 13 y 4.5 14 through 18 y 4.7 19 through 30 y 4.7 31 through 50 y 4.7 51 through 70 y 4.7 > 70 y 4.7 Pregnancy £18 y 4.7 19 through 50 y 4.7 Lactation £18 y 5.1 19 through 50 y 5.1 a AI = Adequate Intake. b UL = Tolerable Upper Intake Level. Data were insufficient to set a UL. In the absence of a UL, extra caution may be warranted in consuming levels above the recommended intake. c All groups except Pregnancy and Lactation represent males and females.
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PART III: POTASSIUM 371 POTASSIUM T he mineral potassium is the main intracellular cation in the body and is required for normal cellular function. The ratio of extracellular to intra- cellular potassium affects nerve transmission, muscle contraction, and vascular tone. Since data were inadequate to determine an Estimated Average Require- ment (EAR) and thus calculate a Recommended Dietary Allowance (RDA) for potassium, an Adequate Intake (AI) was instead developed. The AIs for potassium are based on a level of dietary intake that should maintain lower blood pressure levels, reduce the adverse effects of sodium chloride intake on blood pressure, reduce the risk of recurrent kidney stones, and possibly decrease bone loss. In healthy people, excess potassium above the AI is readily excreted in the urine; therefore a UL was not set. DRI values are listed by life stage group in Table 1. Fruits and vegetables, particularly leafy greens, vine fruit, and root veg- etables, are good food sources of potassium. Although uncommon in the gen- eral population, the main effect of severe potassium deficiency is hypokalemia. Hypokalemia can cause cardiac arrhythmias, muscle weakness, and glucose intolerance. Moderate potassium deficiency, which typically occurs without hypokalemia, is characterized by elevated blood pressure, increased salt sensi- tivity, an increased risk of kidney stones, and increased bone turnover. An inad- equate intake of potassium may also increase the risk of cardiovascular disease, particularly stroke. There is no evidence that a high intake of potassium from foods has ad- verse effects in healthy people. However, for individuals whose urinary excre- tion of potassium is impaired, a potassium intake below the AI is appropriate because adverse cardiac effects (arrhythmias) can occur as a result of hyperkale- mia (markedly elevated serum potassium concentration). Such individuals are typically under medical supervision. POTASSIUM AND THE BODY Function Potassium is the major intracellular cation in the body. Although the mineral is found in both the intracellular and the extracellular fluids, it is more concen- trated in the intracellular fluid (about 145 mmol/L). Even small changes in the
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DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 372 concentration of extracellular potassium can greatly affect the ratio between extracellular and intracellular potassium. This, in turn, affects neural transmis- sion, muscle contraction, and vascular tone. Absorption, Metabolism, Storage, and Excretion In unprocessed foods, potassium occurs mainly in association with bicarbonate- generating precursors like citrate and, to a lesser extent, phosphate. When po- tassium is added to foods during processing or to supplements, it is in the form of potassium chloride. Healthy people absorb about 85 percent of the dietary potassium that they consume. The high intracellular concentration of potassium is maintained by the sodium-potassium-ATPase pump. Because insulin stimulates this pump, changes in the plasma insulin concentration can affect extracellular potassium concentration and thus plasma concentration of potassium. About 77–90 percent of dietary potassium is excreted in the urine. This is because, in a steady state, the correlation between dietary potassium intake and urinary potassium content is high. The rest is excreted mainly in the feces, and much smaller amounts are lost through sweat. DETERMINING DRIS Determining Requirements In unprocessed foods, the conjugate anions of potassium are organic anions, such as citrate, which are converted in the body to bicarbonate. Bicarbonate acts as a buffer, neutralizing diet-derived acids such as sulfuric acid generated from sulfur-containing amino acids found in meats and other high-protein foods. When the intake of bicarbonate precursors is inadequate, buffers in the bone matrix neutralize excess diet-derived acids. Bone becomes demineralized in the process. The resulting adverse consequences are increased bone turnover and calcium-containing kidney stones. In processed foods to which potassium has been added, and in supplements, the conjugate anion is typically chloride, which does not act as a buffer. Because the demonstrated effects of potassium often depend on the ac- companying anion and because it is difficult to separate the effects of potassium from the effects of its accompanying anion, this publication focuses on nonchloride forms of potassium naturally found in fruits, vegetables, and other potassium-rich foods. Since data were inadequate to determine an EAR and thus calculate an RDA for potassium, an AI was instead developed. The AIs for potassium are based on a level of dietary intake that should maintain lower blood pressure
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PART III: POTASSIUM 373 levels, reduce the adverse effects of sodium chloride intake on blood pressure, reduce the risk of recurrent kidney stones, and possibly decrease bone loss. Special Considerations African Americans: Because African Americans have lower intakes of potas- sium and a higher prevalence of elevated blood pressure and salt sensitivity, this population subgroup would especially benefit from an increased intake of po- tassium. (In general terms, salt sensitivity is expressed as either the reduction in blood pressure in response to a lower salt intake or the rise in blood pressure in response to sodium loading.) Individuals with certain conditions: Individuals with Type I diabetes and indi- viduals taking cyclo-oxygenase-2 (COX-2) inhibitors or other nonsteroidal anti- inflammatory (NSAID) drugs should consume levels of potassium recommended by their health care professional. These levels may well be lower than the AI. Impaired urinary potassium excretion: Common drugs that can substantially impair potassium excretion are angiotensin converting enzyme (ACE) inhibi- tors, angiotensin receptor blockers (ARB), and potassium-sparing diuretics. Medical conditions associated with impaired urinary potassium excretion in- clude diabetes, chronic renal insufficiency, end-stage renal disease, severe heart failure, and adrenal insufficiency. Elderly individuals are at an increased risk of hyperkalemia because they often have one or more of these conditions or are treated with one of these medications. Because arrhythmias due to hyperkalemia can be life-threatening, the AI does not apply to people with the above medical conditions or to those taking drugs that impair potassium excretion. In such cases, a potassium intake below the AI is often appropriate. In addition, salt substitutes containing potassium chloride should be cautiously used by these individuals, for whom medical supervision is also advised. Criteria for Determining Potassium Requirements, by Life Stage Group Life Stage Group Criterion 0 through 6 months Average consumption from human milk 7 through 12 months Average consumption from human milk + complementary foods 1 through 18 y Extrapolation of adult AI based on energy intake 19 through >70 y Intake level to lower blood pressure, reduce the extent of salt sensitivity, and minimize the risk of kidney stones in adults
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DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 374 Pregnancy £ 18 through 50 y Age-specific value Lactation £ 18 through 50 y Age-specific values + average amount of potassium estimated in breast milk during the first 6 months (0.4 g/day) The UL The Tolerable Upper Intake Level (UL) is the highest level of daily nutrient intake that is likely to pose no risk of adverse effects for almost all people. In otherwise healthy individuals (i.e., individuals without impaired urinary potas- sium excretion due to a medical condition or drug therapy), there is no evi- dence that a high level of potassium from foods has adverse effects. Therefore, a UL for potassium from foods has not been set. However, supplemental potas- sium can lead to acute toxicity, as well as adverse effects due to chronic con- sumption (see “Excess Intake”). Although no UL for potassium was set, potas- sium supplements should only be provided under medical supervision. SOURCES OF POTASSIUM Foods Fruits and vegetables, particularly leafy greens, vine fruit (such as tomatoes, cucumbers, zucchini, eggplant, and pumpkin), and root vegetables, are good sources of potassium and bicarbonate precursors. Although meat, milk, and cereal products contain potassium, they do not contain enough bicarbonate precursors to adequately balance their acid-forming precursors, such as sulfur- containing amino acids. Nutrient tables of the citrate and bicarbonate content of foods are lacking, making it difficult to estimate the amount consumed of these other food components. Dietary Supplements The maximum amount of potassium found in over-the-counter, multivitamin- mineral supplements is generally less than 100 mg. Bioavailability This information was not provided at the time the DRI values for this nutrient were set.
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PART III: POTASSIUM 375 TABLE 2 Potential Interactions with Other Dietary Substances Substance Potential Interaction Notes POTASSIUM AFFECTING OTHER SUBSTANCES Sodium Potassium bicarbonate Supplemental potassium bicarbonate mitigates the chloride mitigates the pressor effect effects of dietary sodium chloride. The effects seem to of sodium chloride. Dietary be more prominent in African Americans, who have a potassium increases the higher prevalence of hypertension and of salt urinary excretion of sodium sensitivity and a lower intake of potassium than non- chloride. African Americans. Sodium: The sodium:potassium ratio Although blood pressure is inversely associated with potassium is typically more closely potassium intake and directly associated with sodium ratio associated with blood intake and the sodium:potassium ratio, the ratio pressure than with the intake typically is more influential. Given the interrelatedness of either substance alone. of sodium and potassium, the requirement for potassium may depend on dietary sodium intake. The incidence of kidney However, currently there are not enough data on stones has been shown to which to make recommendations. increase with an increased sodium:potassium ratio. Dietary Interactions There is evidence that potassium may interact with certain other nutrients and dietary substances (see Table 2). INADEQUATE INTAKE AND DEFICIENCY The adverse effects of inadequate potassium intake can result from a deficiency of potassium per se, a deficiency of the anion that accompanies it (e.g., citrate), or both. Severe potassium deficiency is characterized by hypokalemia, a condi- tion marked by a serum potassium concentration of less than 3.5 mmol/L. The adverse consequences of hypokalemia include cardiac arrhythmias, muscle weakness, and glucose intolerance. Moderate potassium deficiency, which typi- cally occurs without hypokalemia, is characterized by increased blood pres- sure, increased salt sensitivity, an increased risk of kidney stones, increased bone turnover, and a possible increased risk of cardiovascular disease, particu- larly stroke.
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DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 376 Processed foods and unprocessed foods differ in their composition of con- jugate anions, which in turn, can affect bone mineralization. In unprocessed foods, the conjugate anions of potassium are mainly organic anions, such as citrate, which are converted in the body to bicarbonate. Consequently, an inad- equate intake of potassium is also associated with a reduced intake of bicarbon- ate precursors. Bicarbonate acts as a buffer, neutralizing diet-derived noncarbonic acids such as sulfuric acid generated from sulfur-containing amino acids found in meats and other high-protein foods. If the intake of bicarbonate precursors is inadequate, buffers in the bone matrix neutralize the excess diet-derived acids. Bone becomes demineralized in the process. In processed foods to which po- tassium has been added, and in supplements, the conjugate anion is typically chloride, which does not act as a buffer. Excess diet-derived acid titrates bone, leading to increased urinary calcium and reduced urinary citrate excretion. The possible adverse consequences are increased bone demineralization and an increased risk of calcium-containing kidney stones. Special Considerations Climate and physical activity: Heat exposure and exercise can increase potas- sium loss, primarily through sweat, thereby increasing potassium requirements. Diuretics: Often used to treat hypertension and congestive heart failure, thiazide-type diuretics increase urinary potassium excretion and can lead to hypokalemia. For this reason, potassium supplements are often prescribed. Potassium-sparing diuretics prevent diuretic-induced potassium loss and are often concurrently used with thiazide-type diuretics. Individuals who take di- uretics should have their serum potassium levels regularly checked by their health care providers. Very low-carbohydrate, high-protein diets: Low-grade metabolic acidosis oc- curs with the consumption of very low-carbohydrate, high-protein diets to pro- mote and maintain weight loss. These diets, which may be adequate in potas- sium due to their high protein content, are inadequate as a source of alkali because fruits are often excluded from them. EXCESS INTAKE For healthy individuals, there is no evidence that a high level of potassium intake from foods can have adverse effects. However, potassium supplements can cause acute toxicity in healthy people. Chronic consumption of high levels of supplemental potassium can lead to hyperkalemia (markedly elevated serum
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PART III: POTASSIUM 377 potassium) in people with an impaired ability to excrete potassium. The most serious potential effect of hyperkalemia is cardiac arrhythmia. Gastrointestinal discomfort has been reported with some forms of potas- sium supplements. The specific product or vehicle in which the potassium supplement is provided is the critical determinant of the risk of gastrointestinal side effects. Special Considerations Problem pregnancy: High levels of potassium should be consumed with care by pregnant women with preeclampsia. The hormone progesterone, which is elevated during pregnancy, may make women with undetected kidney prob- lems or decreased glomerular filtration rate (a side effect of preeclampsia) more likely to develop hyperkalemia when potassium intake is high.
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DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 378 KEY POINTS FOR POTASSIUM ✓ Potassium is the main intracellular cation in the body and is required for normal cellular function. The ratio of extracellular to intracellular potassium levels affects neural transmission, muscle contraction, and vascular tone. ✓ The AIs for potassium are based on a level of dietary intake that should maintain lower blood pressure levels, reduce the adverse effects of sodium chloride intake on blood pressure, reduce the risk of recurrent kidney stones, and possibly decrease bone loss. ✓ Since data were inadequate to determine an EAR and thus calculate an RDA for potassium, an AI was instead developed. ✓ Individuals with Type I diabetes; individuals with chronic renal insufficiency, who may take certain medications; and individuals taking cyclo-oxygenase-2 (COX-2) inhibitors or other nonsteroidal anti-inflammatory (NSAID) drugs should consume levels of potassium recommended by their health care professional. These levels may well be lower than the AI. ✓ Because African Americans have lower intakes of potassium and a higher prevalence of elevated blood pressure and salt sensitivity, this population subgroup would especially benefit from an increased intake of potassium. ✓ In healthy individuals, excess potassium above the AI is readily excreted in the urine; therefore, a UL was not set. ✓ Good food sources of potassium include fruits and vegetables, particularly leafy greens, vine fruit, and root vegetables. ✓ Although uncommon in the general population, the main effect of severe potassium deficiency is hypokalemia, which can cause cardiac arrhythmias, muscle weakness, and glucose intolerance. ✓ Moderate potassium deficiency, which typically occurs without hypokalemia, is characterized by elevated blood pressure, increased salt sensitivity, an increased risk of kidney stones, and increased bone turnover.
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PART III: POTASSIUM 379 Chronic consumption of high levels of potassium can lead to 3 hyperkalemia in people with an impaired ability to excrete potassium, The most serious potential effect of hyperkalemia is cardiac arrhythmia. Elderly individuals are often at increased risk of hyperkalemia. 3