Potassium

The average body contains about 140 g of potassium.

What it does in the body

Potassium has many functions in addition to those mentioned above. It is essential for protein synthesis and for the conversion of blood sugar into glycogen. It activates a number of enzymes, particularly those concerned with energy production. It stimulates normal movements of the intestinal tract.

Absorption and metabolism

Absorption of potassium from the diet is passive and does not require any specific mechanism. Absorption takes place in the small intestine as long as the concentration in gut contents is higher than that in the blood. If food moves rapidly through the bowel then absorption will not be sufficient.

The kidneys are the main regulators of body potassium, maintaining blood levels by controlling excretion, even as intake varies. Some potassium is excreted in sweat. Digestive juices contain significant amounts of potassium but most of this is re-absorbed in the lower gut.

Deficiency

Symptoms of severe potassium deficiency include fatigue, vomiting, abdominal distention, acute muscular weakness, paralysis, pins and needles, loss of appetite, low blood pressure, intense thirst, drowsiness, confusion and eventually coma. Muscle spasms, tetany, heart arrhythmias and muscle weakness can also be caused by increased nerve excitability associated with inadequate intake of potassium.

Causes of potassium deficiency include high sodium diets, surgical operations involving the bowel, extensive burns and injuries, diabetes, Cushing's syndrome, excessive excretion of aldosterone, chronic diarrhea which limits gut re-absorption of potassium, persistent vomiting, influenza, inflammatory bowel disease, anemia, ulcerative colitis, kidney disease, heart disease, chronic respiratory failure, prolonged fasting, therapeutic starvation, bizarre diets, anorexia nervosa, alcoholism and cystic fibrosis.

Several medications can also cause potassium deficiency. These include thiazide diuretics, long-term therapy with corticosteroids and adrenal hormones, laxatives, excessive intake of licorice and carbenoxolone, high dose sodium penicillin, intravenous infusions of glucose and salt solutions not containing potassium, ion exchange resins used to reduce blood cholesterol, and insulin.

The sudden death that can occur in fasting, anorexia nervosa or starvation is often a result of heart failure caused by potassium deficiency.

High blood pressure

Many population studies have found links between low potassium intakes and an increased risk of high blood pressure and death from stroke. Increasing the amount of potassium-rich foods in the diet can lead to a reduction in high blood pressure. The ratio of sodium to potassium in the diet appears to play an important role in the development of high blood pressure. The typical Western diet is low in potassium relative to sodium.

Potassium depletion causes the body to retain more fluid in response to a large dose of salt, and high levels of potassium may enhance the excretion of sodium, thus decreasing blood volume and blood pressure.

Sources

Good sources of potassium include fresh fruits, vegetables, soybean flour, shellfish, beans, wheat bran, salad, nuts, cereals, meat, milk, coffee and tea. Many food additives such as potassium iodate used in bread baking, also contain potassium. Potassium is easily lost in cooking and processing foods.

Beet greens, boiled 1 cup 1244 mg

French beans, raw ½ cup 1150 mg

Seeded raisins 1 cup 1136 mg

Snapper, grilled 1 fillet 887 mg

Mackerel, cooked, dry ½ fillet 859 mg

Prunes ½ cup 757 mg

Pistachios ½ cup 665 mg

Avocado ½ avocado 602 mg

Potatoes, fried regular order 541 mg

Potato chips 30g 523 mg

Potato flesh, baked 1 cup 490 mg

Peanuts ½ cup 488 mg

Ham 100g 510 mg

Orange juice 1 cup 471 mg

Melon 1 cup 470 mg

Halibut, grilled ½ fillet 490 mg

Lima beans, boiled ½ cup 461 mg

Apricots, dried 10 halves 482 mg

Bananas 1 fruit 451 mg

Milk 1 cup 424 mg

Green peas, boiled 1 cup 412 mg

Spinach, boiled ½ cup 398 mg

Barley ½ cup 395 mg

Beef 85g 395 mg

Recommended dietary allowances

No RDA has been set in the USA but the estimated minimum requirement for a healthy person is 2000 mg. The typical adult intake may be between 800 mg and 1500 mg. The RNI in the UK is 3500 mg and the RDA in Australia is 1950 to 5460 mg.

Supplements

Potassium supplements are usually in the form of tablets or solutions, often of potassium chloride. Amino acid chelate and protein complexes are also available and these complexes also replace the protein losses which accompany potassium excretion. Potassium is added to sports drinks to help replace that lost in heavy sweating.

Potassium supplements can be irritating to the stomach and should be taken after meals with a glass of water. Slow release or film-coated tablets have been associated with ulcers of the small intestine. The tablets should not be taken with alcohol as this may worsen stomach irritation.

Toxic effects of excess intake

Intakes of potassium in doses larger than 18 000 mg cause muscular weakness, low blood pressure, mental confusion and eventually heart attack. Potassium injection can be fatal. Lower doses can cause nausea, vomiting, diarrhea and abdominal cramps.

A healthy person cannot obtain toxic levels of potassium from the diet. Causes of potassium excess include insufficient production of adrenal gland hormones, acidosis, major infections, and shock after injury in which potassium leaks out of damaged cells into the blood. In severe kidney disease, potassium is not excreted, and excessive levels build up in the tissue.

Therapeutic uses of supplements

Potassium is one of the most commonly prescribed minerals. It is used in situations where body potassium is decreased, such as during diuretic drugs therapy.

High blood pressure

Many studies have found potassium supplements to have beneficial effects in the treatment of high blood pressure. Doses involved usually range from 2.5 to 5 g. In people with normal blood pressure, those who are salt sensitive or who have a family history of hypertension appear to benefit most from potassium supplementation. The greatest blood pressure-lowering effect of potassium supplements occurs in patients with severe hypertension. This effect is pronounced with prolonged potassium supplementation. Potassium may help to lower blood pressure in several ways, including enhancing sodium excretion, by directly dilating blood vessels, or lowering cardiovascular reactivity to body chemicals which constrict blood vessels.

A 1997 analysis of studies on the effects of potassium supplementation on blood pressure confirms that low intake of the mineral plays an important role in high blood pressure, and increasing intake is beneficial in treatment. Researchers at Johns Hopkins University looked at 33 randomized controlled trials with over 2069 participants in which potassium supplements were used. Positive effects were seen with a decrease in mean systolic pressure of 3.11 mm Hg and in diastolic pressure of 1.97 mm Hg. The effects were enhanced in those exposed to a high intake of sodium.1

In a study published in 1998 in the American Heart Association journal, Hypertension, researchers at the Harvard School of Public health tested the effects of potassium, calcium and magnesium supplements on 300 women (average age 39 years) whose dietary intakes of those minerals were low. The women had blood pressure in the normal range. The women were divided into five groups: the calcium (1200 mg per day), magnesium (336 mg per day) and potassium (1600 mg per day) groups; a group who received all three supplements; and a placebo group. The result showed that potassium supplements lowered blood pressure whereas calcium and magnesium supplements did not. The results also showed that those in the three supplements group had smaller falls in blood pressure than those in the potassium group. The researchers speculate that calcium and magnesium might in some way interfere with the blood pressure- lowering effect of potassium.2

Cardiovascular disease

High rates of potassium intake are associated with protection from cardiovascular disease, including stroke, in people in both developing and industrialized countries who eat diets high in unrefined whole grains and vegetables. Potassium may protect against cardiovascular diseases in a number of ways: by reducing free radical formation; proliferation of vascular smooth muscle cells; platelet aggregation; and blood clotting.3 Potassium supplements are used to treat heart arrhythmias.

Kidney stones

Higher potassium intakes may be beneficial in preventing kidney stones formation. Researchers at the Kaiser Permanente Medical Centers in Northern California have found that giving potassium-magnesium citrate to kidney stone sufferers reduces the risk of them developing further stones. The stones were of the calcium oxalate type. In the double-blind study reported in the Journal of Urology, 64 patients were given either a placebo or the potassium-magnesium citrate compound for up to three years. New kidney stones occurred in 63.6 per cent of the patients taking placebo, but in only 12.9 per cent of those taking the potassium-magnesium citrate compound.4

Other uses

Potassium supplements may be of benefit in early menopause to combat fatigue and mood swings. It can also be used to treat infant colic, allergies and headache. During and after diarrhea, potassium replacement may be necessary.

Interactions with other nutrients

Aside from the interactions with other electrolytes discussed above, potassium may have a role in maintaining normal calcium balance in the body as potassium decreases urinary loss of calcium.

Interactions with drugs

Diuretic drugs, particularly the thiazide variety, act by increasing the output of sodium and water from the kidneys but at the same time, potassium excretion is increased. Antibiotics taken on a long-term basis can deplete potassium. High intakes of alcohol, coffee and sugar may lead to potassium deficiency.

Cautions

Those with dehydration, heat cramps, ulcers, kidney disease or who are taking drugs which cause the kidney to retain potassium should avoid potassium supplements.

1 Whelton P K et al. Effects of oral potassium on blood pressure. JAMA 1997;277:1624-1632

2 Sacks FM, Willett WC, Smith A, Brown LE, Rosner B, Moore TJ. Effect on blood pressure of potassium, calcium, and magnesium in women with low habitual intake. Hypertension 1998 Jan;31(1):131-138

3 Young DB, Lin H, McCabe RD. Potassium's cardiovascular protective mechanisms. Am J Physiol 1995 Apr;268(4 Pt 2):R825-R837

4 Ettinger B et al. Potassium magnesium citrate is an effective prophylaxis against recurrent calcium oxalate nephrolithiasis. Journal of Urology 1997;158:2069-73