Potassium is the main positively charged ion found inside cells. It is actively pumped inside cells by millions of sodium-potassium pumps so that its concentration inside cells is 30 times greater than in the surrounding, extracellular fluid. This generates a small, negative, electrical charge across the cell membrane which is essential for life.
The flow of potassium in and out of cells allows muscles to contract, the heart to beat, nerves to conduct messages, and regulates the production of energy.
Because high or low potassium levels can affect vital functions, its concentration within the blood is tightly controlled within a narrow range.
The sodium-potassium pumps in kidney cells ensure the potassium is retained in the body in exchange for sodium, so that excess sodium is flushed from the body via the urine. This draws excess water away from the body, too, through the effects of osmosis, to reduce fluid retention and help maintain a normal blood pressure.
Excess dietary sodium is linked with high blood pressure in some people, whose kidneys are unable to process sodium as efficiently as others. As a result, a diet that is relatively high in potassium and low in sodium is linked with a lower risk of developing hypertension and of experiencing a stroke. In one study, over 80 per cent of people taking antihypertensive medication were able to halve their drug doses (under medical supervision) just by increasing their dietary intake of potassium.
Foods that contain potassium include seafood, fruit (particularly tomatoes and bananas), vegetables, whole grains and low-sodium potassium-enriched salts.
Most people do not need potassium supplements. Low levels of potassium can develop in people taking certain diuretics that do not have a potassium-sparing action. Symptoms that may be due to lack of potassium include poor appetite, fatigue, weakness, low blood glucose, muscle cramps, irregular or rapid heartbeat, constipation, irritability, pins and needles, drowsiness and confusion.
High potassium levels are rare as the body usually controls blood levels well. They can occur in people with kidney problems, or those who take excess potassium supplements, to produce symptoms such as irregular heartbeat, and muscle fatigue.
The EU RDA for potassium is 2000mg (ie 2 g). The upper safe level for long-term use from supplements is suggested as 3700mg.
Potassium supplements should not be taken by anyone who is taking a type of medication called an ACE inhibitor or who has kidney disease, except under medical advice.
By Dr Sarah Brewer, originally published on www.mylowerbloodpressure.com. Twitter: @DrSarahB