Potassium in nutrition and human health

To maintain life and health, the diet of humans must contain the chemical element,potassium, in its ionic form (K⁺), usually consumed as potassium salts of organic acids in food (e.g., potassium citrate), found most abundantly in non-grain plant foods (vegetables and fruits). In 2004-2006, and again in 2010, the Institute of Medicine of the National Academies of Science  and its Food and Nutrition Board  recommended that adult humans consume 4700 milligrams (mg) of potassium per day, or more, which, calculated from the atomic mass of potassium (39.1 mg per mmol), corresponds to 120 millimoles (mmol) potassium per day: 4700 mg/39.1 mg/mmol=120 mmol. That recommended intake of potassium substantially exceeds estimates from recent surveys of average intakes by the general population, raising the possibility that a persisting state of suboptimal body potassium content, and rate of throughput of potassium, prevails in the general population.   

Subsequent sections will discuss potassium intake recommendations for children and special groups, as well as more recent perspectives on the 'optimal' requirements for dietary potassium in humans.

General considerations

Potassium ranks as the most abundant cation (positive ion) inside animal cells (intracellular), and as such contributes critically in numerous important ways to the optimal functioning of cells and therefore to optimal functioning of the organ systems and individuals they compose. Among other metabolic functions, potassium plays a role in the synthesis of proteins and in the biochemical transformations required for carbohydrate metabolism.

Potassium plays an esential role in maintaining the electrical potential difference across the cell's plasma membrane, the intra- to extra-cellular electrical potential difference, typically referred to as the 'membrane potential'. That physicochemical regulatory function importantly enables normal transmission of information along nerves (nerve impulse transmission), normal contraction of muscle fibers, and normal functioning of the heart. The concentration of potassium inside cells (the intracellular fluid) exceeds that outside cells (the extracellular fluid) by an order of magnitude (~30 times), whereas the extracellular concentration of sodium exceeds that of its intracellular concentration by an order of magnitude (~10 times), the reverse of the situation with potassium. Those concentration differences between potassium ions and sodium ions generates the membrane potential, the inside potential negative with respect to the outside potential. A protein-based ion-pumping mechanism located within the lipid bilayer of the....

By influencing the electrical potential difference across the cell membrane, the ratio of the concentrations of potassium in intracellular fluid (ICF) to that in the cells' surrounding extracellular fluid (ECF) has important effects on the rate of transmission of electrical activity (pulses) along nerve fibers and skeletal muscle cells, which, among other things, affects the degree of contraction of the smooth muscles of arteries and arterioles (vascular tone). Inasmuch as extracellular potassium varies in the 3-6 mmol/L range, while intracellular potassium concentrations average about 145 mmol/L, small changes in extracellular potassium concentration have a greater effect on the ICF-to-ECF potassium concentration ratio than similar small changes in intracellular potassium concentration. Subsequent sections discuss the implication of changes in the ICF-to-ECF potassium concentration ratio in human physiology.

In healthy persons whose daily consumption of potassium does not vary greatly, the amount of potassium consumed equals the amount excreted, by the kidney and gastrointestinal tract predominantly. Physiologists refer to that equality as zero net external body potassium balance. Of the major electrolytes, potassium has the highest ratio of potassium consumed to the amount of potassium in the extracellular compartment, a characteristic that presents a challenge in maintaining extracellular potassium concentrations within a set range in the face of variations in daily potassium intake, a challenge met by efficient excretion and somewhat less efficient conservation, mediated by homeostatic mechanisms not completely elucidated.

Disturbances relating to body potassium deficiency may result from:

• prolonged inadequate consumption of potassium-containing foods;
• inappropriately large rates of excretion of potassium in urine;
• inappropriately large excretion rates of potassium in feces.

Disturbances relating to body potassium excess may result from:

• drugs and kidney diseases that impair the kidney’s ability to excrete potassium in urine;
• deficiency of hormones that act to promote kidney and gastrointestinal excretion of potassium.

Subsequent sections will elaborate on the above concepts.

Requirements for potassium consumption by humans

Humans must habitually consume potassium because the body does not store it (as it does fat, say), while the kidney continues to excrete it in the urine even when potassium intake ceases. Potassium-rich foods include leafy green vegetables, vine fruits (e.g., squash, tomatoes, cucumbers, etc.), root vegetables, and tree fruits (see below).

The Institute of Medicine of the National Academies of Science and its Food and Nutrition Board recommend as "Adequate Intake" (AI) of potassium, in mmol/day, as 77 and 97 for children ages 1-3 and 4-8 years, respectively, and as 115 and 120 for children 9-13 and 14-18 years, respectively. For adult men and women, ages 19 to >70 years, they recommend an AI of potassium as 120 mmol/day, and the same amount for pregnant women as young as 14 years, increasing to 130 mmol/day for lactating women.

The Institue of Medicine of the National Academies of Science claims:

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.

The claim reflects concerns about inadequate potassium consumption as

• contributing to hypertension (abnormally high arterial blood pressure) through its effects to constrict the small arteries (arterioles) that deliver blood to muscles and other organs, and to promote renal retention of sodium chloride);
• mitigating the effect of dietary sodium chloride ('salt') in contributing to hypertension, to kidney stone formation, and to osteoporosis (soft, fracture-prone bones).

 • Actual consumption of potassium by Americans, 2005 - 2010

The U.S. Department of Agriculture has released the results of the National Health and Nutrition Examination Survey (NHANES) data for 2005-2006, 2007-2008, and 2009-2010, giving the average values for the consumption of various nutrients, including potassium.  The table below shows the average values for potassium consumption by Americans (2005-2010) with the recommended amounts given in the preceding section.

Potassium Intake What We Eat in America 2005-2006, 2007-2008, 2009-2010 Years Gender Potassium mmol/day % Of Recom- mended 2005-2006 Men 81 68 2005-2006 Women 61 50         2007-2008 Men 78 65 2007-2008 Women 58 50         2009-2010 Men 81 68 2009-2010 Women 61 50 Recommended “Adequate Intake”, 120 mmol/day, identical for men and women, and therefore not adjusted for differences in body size or lean body mass between men and women. Because the Food and Nutrition Board indicated that eating ordinary foods imposed no danger of consuming excess potassium except in certain potassium non-tolerant conditions, most Americans could likely achieve “adequate intakes” or more, by doubling their potassium intake.

Note that average consumption of potassium by adults falls well below recommended amounts, with American women consuming half the recommended amount on average, and American men about two-thirds. Those findings do not indicate improvement in achieving "adequate intakes" over the findings reported for years 2003-2004. 

Children and adolescents showed a similar range of insufficiencies of potassium consumption in the two reports.  

More recent analyses find that most Americans under-consume vegetables and fruit, the richest food sources of potassium.

Without increasing total energy (calorie) intake, Americans could increase potassium consumption to achieve "adequate intake" by reducing intake of potassium-poor foods and increasing intake of potassium-rich foods.

Potassium Content of Foods

Understanding the biological effects of dietary potassium ions (cations) requires an associated understanding of the nature of the negatively charged ions (anions) that accompany potassium in foods, balancing potassium’s positive charge, thus maintaining electroneutrality. In natural diets not subjected to commercial processing that includes addition of potassium salts—typically potassium chloride—a variety of organic anions (e.g., citrate, fumarate) accompany the potassium ions in foods, in amounts sufficient to nearly balance the positive charge of the potassium ions (i.e., in near chemical equivalent amounts). Following their absorption by the gastrointestinal tract, the body converts a large fraction of those organic anions to bicarbonate (an acid-neutralizing substance, or base), as an end-product of metabolism. Thus, diets with differing amounts of potassium exert potassium-induced biological effects associated and often interacting with the effects of the differing amounts of acid-neutralizing base, bicarbonate, as generated by the body from the potassium-accompanying organic anions. Physiologists often cannot dissect out the specific effects of the co-ions potassium and bicarbonate, when, for example, a person increases their dietary intake of potassium-rich foods, which typically contain bicarbonate-generating organic anions in abundance (see Table 1 and accompanying text).

Table 1 shows the potassium content of the major food groups, indicating the relation of potassium content to the net acid (or bicarbonate) load supplied to the body by each food group (see comments following table). [NB: Because potassium ions have a single charge (univalent), 1 millimole (mmol) of potassium equals 1 milliequivalent (meq) of potassium.]

Table 1. Potassium Content of the Major Food Groups: Relation to the Net Acid Load Accompanying Potassium

Food Group # items/group Net Acid Load Potassium Content Protein Content Protein Content meq/100 kcal meq/100 kcal g/100 kcal g/100 meq potassium Acid-Producing Food Groups Fish 8 14.6 8.1 16.8 207 Meat 3 12.4 7.6 18.4 242 Poultry 2 7.8 4.7 13.4 287 Eggs 1 7.3 2.4 8.3 339 Shellfish 3 7.3 18.4 18.0 159 Cheese 9 3.3 0.8 7.1 982 Milk 4 1.3 6.4 5.7 90 Cereal Grains 7 1.1 2.6 3.2 153 Mean Values 6.9 6.4 11.4 308 Nearly-Neutral Food Groups Legumes 6 -0.4 12.6 10.6 100 Bicarbonate-Producing Food Groups Nuts 6 -1.1 3.8 25.0 86 Fresh Fruits 11 -5.2 9.4 1.6 16 Tubers 2 -5.4 11.8 2.2 18 Mushrooms 1 -11.2 62.3 25.7 41 Roots 5 -17.1 34.3 6.8 21 Vegetable (Vine) Fruits 1 -17.5 35.5 5.6 16 Leafy Greens 6 -23.4 43.5 10.0 24 Plant Stalks 1 -24.9 54.8 4.6 8 Mean Values -13.2 31.9 7.4 29

In Table 1, positive (+) and negative (–) values of net acid load represent acid-producing and bicarbonate-producing equivalents, respectively, in the units specified. Values of net acid load: calculated first for individual food items then averaged per food group, as per compositional values in:. Acid load calculations: as described in: Note that net acid-producing foods tend to have much higher ratios of protein-to-potassium than do net bicarbonate-producing foods (regression of net acid load against Protein/Potassium, r=0.48, p=0.05). Note the relatively low values of protein and potassium in the cereal grain group, of which whole grains comprised six of the seven items in the group.

Table 1 reveals a number of important aspects of food potassium:

• Per unit energy content (kilocalories, abbrev: kcal), non-cereal-grain plant foods provide the most abundant source of potassium.
• The top five plant-food sources of potassium (meq/kcal): root vegetables (celeriac, rutabaga, turnips, carrots, parsnips, sweet potato, potato, yams, onions); vegetable fruit (aka vine fruit) (tomatoes, zucchini, eggplant, cucumbers); leafy greens (spinach, lettuce, kale, chard); stalks (celery, broccoli stalks); mushrooms (not strictly a plant).
• The food sources richest in potassium also supply bicarbonate to the body, as indicated by negative values of "net acid load".
• The potassium content in acid-producing foods (animal-source foods and cereal grains) average about one-fifth that of plant-source foods, which do not contain sufficient quantities of bicarbonate-generating organic anions to neutralize the acid generated from protein and other sustances they contain.
• The ratio of protein-to-potassium in plant-source foods falls short of animal-source foods by a factor of 10.
• Legumes provide moderate amounts of potassium with little or no acid or bicarbonate load.

Table 2 lists selected food sources of potassium, showing amounts of potassium for standard portions, in descending order of amount of potassium per 100 kilocalorie of food source. Raw data for the calculations: taken from

Table 2

Food, Standard Amount Potassium (mg) Kilocalories Potassium (mmol) Potassium (mmol/100 kcal) Beet greens, cooked,1/2cup 655 19 17 88 Spinach, cooked,1/2cup 419 21 11 51 Tomato juice,3/4cup 417 31 11 34 Tomato paste,1/4cup 664 54 17 31 Tomato puree,1/2cup 549 48 14 29 Winter squash, cooked,1/2cup 448 40 11 29 Blackstrap molasses, 1 Tbsp 498 47 13 27 Tomato sauce,1/2cup 405 39 10 27 Cantaloupe,1/4medium 368 47 9 20 Carrot juice,3/4cup 517 71 13 19 Honeydew melon,1/8medium 365 58 9 16 Sweetpotato, baked, 1 potato (146 g) 694 131 18 14 Cod, Pacific, cooked, 3 oz 439 89 11 13 Apricots, dried, uncooked,1/4cup 378 78 10 12 Lima beans, cooked,1/2cup 484 104 12 12 Milk, non-fat, 1 cup 382 83 10 12 Yogurt, plain, non-fat, 8-oz container 579 127 15 12 Rockfish, Pacific, cooked, 3 oz 442 103 11 11 Clams, canned, 3 oz 534 126 14 11 Potato, baked, flesh, 1 potato (156 g) 610 145 16 11 Orange juice,3/4cup 355 85 9 11 Peaches, dried, uncooked,1/4cup 398 96 10 11 Halibut, cooked, 3 oz 490 119 13 11 Tuna, yellowfin, cooked, 3 oz 484 118 12 10 Bananas, 1 medium 422 105 11 10 Plantains, cooked,1/2cup slices 358 90 9 10 Prune juice,3/4cup 530 136 14 10 White beans, canned,1/2cup 595 153 15 10 Soybeans, green, cooked,1/2cup 485 127 12 10 Buttermilk, cultured, low-fat, 1 cup 370 98 9 10 Yogurt, plain, low-fat, 8-oz container 531 143 14 9 Kidney beans, cooked,1/2cup 358 112 9 8 Lentils, cooked,1/2cup 365 115 9 8 Split peas, cooked,1/2cup 355 116 9 8 2% milk, 1 cup 366 122 9 8 Prunes, stewed,1/2cup 398 133 10 8 Soybeans, mature, cooked,1/2cup 443 149 11 8 Rainbow trout, farmed, cooked, 3 oz 375 144 10 7 Yogurt, plain, whole milk, 8 oz container 352 138 9 7 Pork loin, center rib (roasts), lean, roasted, 3 oz 371 190 9 5 Pork chop, center loin, cooked, 3 oz 382 197 10 5

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The Paleolithic Perspective on the 'Optimal' Dietary Requirement of Humans

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Potassium deficiency in type 2 diabetes mellitus and in the metabolic syndrome

Potassium deficiency — or at least suboptimal body content of potassium — may play an important role in causing, sustaining or aggravating type 2 diabetes mellitus and/or metabolic syndrome.

The metabolic syndrome, a serious disturbance of body metabolism and physiology, consists of resistance of certain cell types of the body (e.g., fat cells, skeletal muscle cells) to the ability of the hormone insulin to promote cellular entry of the energy-rich molecule, glucose. Patients with the syndrome may show the following abnormalities: high blood pressure (or use of drugs to control hypertension); high levels of serum triglycerides; low levels of high-density lipoprotein (HDL) cholesterol; overweight, in particular visceral obesity (obesity manifested by abnormally increased abdominal girth); and, detectable levels of the protein, albumin, in the urine (microalbuminuria). The abnormalities of triglyceride levels typically associate with other blood fat disturbances (dyslipidemia) that foster atherosclerosis (buildup of plaques in artery walls that predispose to reduced blood flow to vital organs (e.g., the heart) and to formation of blood clots that can break off and plug vital vessels to the brain, causing stroke). The biochemical factors that promote clot formation are also stimulated in the metabolic syndrome, and the syndrome appears to be one of a chronic state of inflammation, the typical body response to tissue injury. Overweight and obese children show a strong correlation between biochemical markers of inflammation and the metabolic syndrome and insulin resistance, suggesting early-in-life involvement of inflammation related to overweight.

An etimated 50 million Americans have the metabolic syndrome.

Studies in humans using a technique called nuclear magnetic resonance spectroscopy found cellular potassium deficiency in patients with type 2 diabetes mellitus and in patients with hypertension. The use of such a state-of-the-art technique enabled discovery of intracellular potassium deficiency not likely expected from routine clinical tests.

In addition, the studies indicated more acidity in the cells of patients with hypertension, especially those also having diabetes.

A longitudinal study of nearly two thousand men and women in Finland (ages 35-64 years) found no evidence of an association of potassium intake (indexed as 24-hour urinary potassium excretion) and the incidence of type 2 diabetes. Higher sodium chloride intakes did predict the incidence of type 2 diabetes among the subjects. Yet, from the study data reported, one cannot tell if the authors performed the same type of data analysis for potassium as they did for sodium, nor did they examine whether the ratio of sodium-to-potassium had a stronger association with diabetes incidence than did sodium alone. If the latter, that might suggest that higher potassium intakes, to lower the sodium-to-potassium ratio, might mitigate or eliminate the association with diabetes incidence.

Another studied showed that a dietary pattern emphasizing fruit (a potassium-rich food), and deemphasizing foods not especially rich in potassium, reduced the risk of type 2 diabetes.

Studies of close to 500 women (teachers) in Iran showed that increasing intake of fruits and vegetables — potassium-and alkali-rich foods — proportionately decreased the chances of the participants having metabolic syndrome, by 30-35%. The investigators also found that higher fruit and vegetable intakes associated with lower levels of a conventional biomarker of inflammation, a common concomitant of the metabolic syndrome.

Patients with the adrenal gland disorder, primary aldosteronism, have excessively high levels of aldosterone, a hormone that acts on the kidney to cause it to retain sodium and waste body potassium in the urine. They have low levels of the fat-cell-secreting hormone, adiponectin, resulting in insulin resistance. The patients commonly have the metabolic syndrome. Among patients with the metabolic syndrome, the lower their potassium levels the lower their adiponectin levels and the greater their insulin resistance. Though only a study of correlation, the study provides further suspicion that potassium deficiency may play a role in the pathogenesis of the metabolic syndrome.

 • Clinical identification of the metabolic syndrome

• From: Source: National Cholesterol Education Program, Third Report of the Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III), National Heart, Lung, and Blood Institute, National Institutes of Health, May 2001, and the Grundy Report in 2004.

See Table 1, page 435 of Grundy et al.

RISK FACTOR   DEFINING LEVEL   Abdominal Obesity   Waist Circumference   Men   >102 cm (>40 in)   Women   >88 cm (>35 in)   Triglycerides   =/>150 mg/dL   HDL Cholesterol      Men   <40 mg/dL   Women   <50 mg/dL   Blood Pressure   =/>130 (systolic) / =/>85 mm (diastolic) Hg   Fasting Blood Glucose   =/>110 mg/dL

Overweight and obesity associate statistically with insulin resistance and the metabolic syndrome. But abdominal obesity assiciate more strongly with the metabolic risk factors than does an elevated body mass index (BMI), a qualified index of body fatness. Therefore, NHLBI recommends the simple measure of waist circumference to identify the body weight component of the metabolic syndrome. Some male patients develop multiple metabolic risk factors with waist circumferences only marginally increased, e.g., 94-102 cm (37-39 in). Such patients may have a strong genetic contribution to insulin resistance. They should benefit from changes to living a more healthful lifestyle — including attention to diet quantity and composition, and to exercise — similarly to men with categorical increases in waist circumference.

Potassium Intake, Blood Pressure Regulation, and Risk of Heart Disease and Stroke

Intervention-type research in humans has found that raising potassium intakes reduces blood pressure in the arteries (arterial hypertension). In both the population at large and in people with “high blood pressure” (aka “hypertension”), increasing potassium intake by 30-60 meq/day within the range of low (e.g., 30 meq/day) to high (e.g., 200 meq/day) intakes——either from food or prescribed supplements——tends to lower blood pressure. The degree of blood pressure-lowering depends on a variety of factors, including amount of increase in potassium intake and ancestry.

Because people with higher blood pressures have greater risks of death from heart disease (e.g., heart attacks) and stroke (blockage or leakage of blood vessel in the brain), dietary potassium’s effect in helping keep blood pressures lower in part justified setting the recommended intake of potassium at 120 meq/day---substantially higher than the population average---for American adults by the Institute of Medicine in 2005.

These correspondences in part helped justify the Institute of Medicine’s recommendation to American adults to increase their intake of potassium to 120 meq/day:

• Risk both for heart disease and stroke increases in people with hypertension

• Blood pressures decrease with higher potassium intakes.

• Higher potassium intakes reduce stroke risk independent of blood pressure.

The IOM makes no statement whether 120 meq/day potassium intake ‘’optimizes’’ cardiovascular health, but it sets no upper limit restrictions on potassium intake from food, which could reach 200-300 meq/day. Diets that potassium-rich include diets emphasizing the available abundant variety of potassium-rich vegetables and fruits, and deemphasizing fatty animal-source foods (like fatty hamburger meat) and high-fat-or-high-refined-carbohydrate foods with little-or-no additional nutrient content (like vegetable oil or pancake syrup)—diets considered health-fostering in many ways besides mitigating high blood pressure tissue injury.

Research has not determined optimal potassium intake ranges for maximal protection against heart disease and stroke and other detrimental effects of hypertension.

Because high sodium intake has also been implicated in the pathogenesis of hypertension and cardiovascular disease (CVD), investigators have considered the possibility that the relative amounts of sodium and potassium in the diet might be important. The Trials of Hypertension Prevention Collaborative Research Group report that in people with borderline or pre-hypertension, a higher ratio of sodium-to-potassium, estimated from 24-hour urinary excretion rates of the two ions, better estimates the risk of CVD than the intake of either considered separately:

In observational analyses of the mean urinary excretion during 1-1½ to 3 years, we found a suggested positive relationship of urinary sodium excretion and a suggested inverse relationship of urinary potassium excretion with risk of CVD, but neither was statistically significant when considered separately. Both measures strengthened when modeled jointly, with opposite but similar effects on risk. However, the sodium to potassium excretion ratio displayed the strongest and statistically significant association, with a 24% increase in risk per unit of the ratio that was similar for CHD [coronary heart disease] and stroke and was consistent across subgroups.

Dietary Potasium and Risk of Osteoporosis

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Dietary Potassium and Risk of Kidney Stones

[...in progress...]