Potassium

Potassium is an essential mineral and electrolyte found mainly inside cells — about 98% of the body’s potassium is inside cells, with only about 2% in the blood and other fluids outside them. That distribution isn’t incidental: every cell actively maintains it, and it’s fundamental to how nerves fire, muscles contract, and the heart beats. Blood potassium is kept within a narrow range (about 3.5–5.0 mmol/L) — even modest deviations above or below it can cause symptoms, which is why the kidneys, adrenal glands, and hormones such as insulin and aldosterone work continuously to regulate it.

The Sodium-Potassium Pump

The mechanism behind most of potassium’s functions is the sodium-potassium pump (Na⁺/K⁺-ATPase), an enzyme embedded in the membrane of every cell. In each cycle, it moves three sodium ions out of the cell and two potassium ions in, using one molecule of ATP. This creates an electrochemical gradient across the cell membrane — a stored charge — that powers nerve signals, muscle contraction, and the transport of nutrients into cells. It’s one of the most energy-expensive processes in the body, estimated to use around 20–40% of the body’s energy at rest. When blood potassium falls too low or rises too high, this electrical balance is disturbed — which is why abnormal potassium levels affect the muscles and heart so quickly.

AI (Adequate Intake)

Potassium doesn’t have a formal RDA. Instead, it has an Adequate Intake (AI) — used when there isn’t enough evidence to set an RDA, but a target intake can still be defined.

Source: US National Academies (2019), via the NIH Office of Dietary Supplements. The daily value used on food labels is 4,700mg, based on an older, higher recommendation.

ODA (Optimal Daily Allowance)

3,500–4,700mg a day for most adults, from food. This is one of the few nutrients where aiming above the official intake is well supported: the World Health Organization recommends at least 3,510mg a day for adults to help control blood pressure and lower the risk of heart disease and stroke, and the potassium-to-sodium balance matters even more if your diet is high in salt. Get it from fruits, vegetables, legumes, nuts, and dairy rather than supplements. The exception: people with kidney disease, or who take medicines that raise potassium levels (see Interactions), may need to limit potassium — check with your doctor.

Found In (per 100g)

Per 100g, nuts, seeds, and dried fruit lead — dried apricots are among the very richest sources — but portion size changes the picture. Bananas are famous for potassium, yet a medium potato cooked in its skin, a cup of cooked lentils or beans, or a serving of cooked spinach provides as much or more. Avocados, tomatoes, oranges, melon, milk, and coconut water are also good sources. Boiling leaches some potassium into the cooking water, so steaming, baking, or using the cooking liquid keeps more of it.

Helps With

• Maintaining fluid and electrolyte balance in and around cells
• Healthy blood pressure — potassium helps the kidneys excrete sodium and relaxes blood vessel walls, blunting sodium’s blood-pressure-raising effect. In trials, increasing potassium lowered blood pressure, especially in people with high blood pressure
• Lower risk of stroke and cardiovascular disease — higher potassium intakes are linked with fewer strokes, and in a large 2021 trial in China (SSaSS), replacing regular salt with a potassium-enriched salt substitute reduced strokes by 14% and deaths by 12%
• Nerve signal transmission
• Muscle contraction and relaxation (including the heart)
• Preventing kidney stones — potassium citrate is a standard treatment for some types of kidney stones, and diets rich in fruit and vegetables are linked with fewer stones
• Bone health — potassium-rich fruits and vegetables, and potassium bicarbonate and citrate, reduce calcium loss in urine; effects on bone density in trials have been mixed

For Athletes and Active People

Potassium is lost in sweat, but in much smaller amounts than sodium — sweat typically contains several times more sodium than potassium. And during exercise, blood potassium actually rises, as working muscles release it; it then falls back afterwards as muscles take it back up. So, contrary to popular belief, exercise-associated muscle cramps are rarely caused by low potassium — they seem to be driven mainly by muscle fatigue. For most athletes, sweat losses are easily replaced by normal meals.

That said, a potassium-rich diet matters for long-term health and blood pressure, and genuine low potassium (hypokalemia) — usually from vomiting, diarrhea, diuretics, or very restrictive dieting rather than training — causes muscle weakness and fatigue, and raises the risk of dangerous heart rhythms. The best way to cover your needs after training is food rather than supplements: potatoes, beans, lentils, dried fruit, bananas, and yogurt deliver potassium alongside carbohydrate, protein, and other recovery nutrients.

One less obvious point: magnesium deficiency can keep potassium levels low even with adequate potassium intake, because low magnesium causes the kidneys to waste potassium. If low potassium isn’t responding to treatment, doctors check magnesium — the two have to be corrected together.

Insufficient Doses

Many people eat less potassium than recommended — mostly because of diets low in fruit, vegetables, and legumes and high in processed foods. Low intake rarely causes low blood potassium in healthy people, because the kidneys conserve it, but it contributes to higher blood pressure and cardiovascular risk over time. Clinically low blood potassium (hypokalemia) usually results from losses.

Risk of low blood potassium is higher in:

• People with frequent vomiting or diarrhea — digestive losses deplete potassium quickly
• People using diuretics — loop and thiazide diuretics increase potassium loss in urine
• People with conditions that raise aldosterone (such as primary aldosteronism) — this adrenal hormone increases potassium excretion
• People with alcohol dependence — poor diet combined with increased losses
• People with eating disorders that involve vomiting or laxative misuse — which can cause severe, dangerous potassium losses
• People with magnesium deficiency — low magnesium causes low potassium that won’t correct until magnesium is restored
• Very heavy sweaters doing prolonged exercise in the heat, in combination with poor intake — though sweat losses alone rarely cause low potassium

Symptoms of low blood potassium (hypokalemia):

• Fatigue and muscle weakness
• Muscle cramps and twitching
• Constipation
• Tingling or numbness
• Irregular heartbeat or palpitations
• In severe cases: paralysis and life-threatening heart rhythm problems

Because almost all of the body’s potassium is inside cells, a blood test doesn’t always reflect total body stores — doctors interpret results alongside symptoms, medicines, and other tests.

Excessive Doses

No upper limit has been set for potassium from food, because healthy kidneys excrete the excess efficiently. High blood potassium (hyperkalemia) is mainly a risk for people with reduced kidney function, people taking medicines that raise potassium (see Interactions), and people taking potassium supplements in large amounts.

Symptoms of hyperkalemia:

• Nausea and vomiting
• Muscle weakness, tingling, and fatigue
• Slow or irregular heartbeat
• In severe cases, cardiac arrest — often with few warning signs, which is why at-risk people have their levels monitored

Why potassium supplements are capped at 99mg: in the US, most over-the-counter potassium supplements contain no more than 99mg per dose — a tiny fraction of daily needs. The cap traces back to the 1960s, when concentrated potassium chloride tablets were found to cause ulcers in the small intestine, and the FDA required warnings on higher-dose tablets. Higher-dose potassium is available on prescription for treating deficiency, because doses large enough to correct low potassium need medical monitoring.

Different Types

• Potassium Chloride — the most common form, used in prescription supplements and in low-sodium salt substitutes. Effective but can irritate the stomach and has a bitter, metallic taste in larger amounts.
• Potassium Citrate — gentler on the stomach, and it makes urine less acidic, which is why it’s prescribed to prevent some types of kidney stones. A good general-purpose form.
• Potassium Gluconate — mild and well tolerated; common in over-the-counter supplements. Provides less potassium per gram than the chloride form.
• Potassium Bicarbonate — an option for people sensitive to chloride. Like citrate, it neutralizes acid, and in some studies it reduced calcium loss in urine — of possible interest for people on high-protein diets, though benefits for bone density aren’t established.
• Potassium Phosphate — used mainly in medical settings, including intravenously, often when phosphate also needs replacing; not a practical everyday supplement.

None of these forms are suitable for people with kidney disease, or for people taking medicines that raise potassium, without medical advice.

Which form for your goal:

How to Take It

The 99mg cap on most over-the-counter supplements makes it difficult — and usually unnecessary — to supplement potassium the way you might supplement magnesium or calcium. The better approach is to eat plenty of potassium-rich foods, particularly vegetables, fruits, legumes, nuts, and dairy.

If you do take a supplement, take it with food to reduce stomach irritation, and spread doses through the day. If you take ACE inhibitors, ARBs, potassium-sparing diuretics, or other medicines that raise potassium, or have any kidney condition, speak to a doctor before using potassium supplements or potassium-based salt substitutes — these combinations can push blood potassium to dangerous levels.

The balance of potassium to sodium in your diet matters as much as the amount of potassium. Eating fewer processed foods (high in sodium) and more whole foods (high in potassium) improves the balance without supplements for most people — and for those without kidney problems, a potassium-enriched salt substitute is a simple, evidence-backed swap.

Interactions

Loop diuretics (such as furosemide and bumetanide) and thiazide diuretics increase potassium loss. ACE inhibitors, ARBs, potassium-sparing diuretics (such as spironolactone and amiloride), and some other medicines — including NSAID painkillers taken regularly and the antibiotic trimethoprim — raise potassium levels and can cause hyperkalemia when combined with potassium supplements or potassium-based salt substitutes. Laxative misuse depletes potassium through digestive losses.

Synergy

• Works with sodium to maintain fluid balance and blood pressure — the two are best understood as a ratio, not as separate values.
• Works with magnesium for muscle contraction and nerve function, and magnesium is needed for the body to hold on to potassium.
• Works alongside calcium in blood pressure regulation and bone health — potassium-rich diets reduce calcium loss in urine.

Antagonistic Interactions

• High sodium intake counteracts potassium’s blood pressure benefits.
• Magnesium deficiency impairs the body’s ability to retain potassium.
• Chronic kidney disease reduces the body’s ability to excrete potassium, so even normal intakes can become a risk.
• Excess aldosterone (for example, from adrenal tumours) drives potassium loss regardless of intake.

Food values: USDA FoodData Central — pistachios, raw (Foundation Foods, FDC ID 2515379); raisins, dark, seedless (Foundation Foods, 2758980); almonds, raw (Foundation Foods, 2346393); pumpkin seeds (pepitas), raw (Foundation Foods, 2515380); sweet potato, baked (SR Legacy, 168483); spinach, boiled (SR Legacy, 168463); potatoes, microwaved in skin, flesh and skin (SR Legacy, 170094); edamame, prepared (SR Legacy, 168411); kidney beans, cooked (SR Legacy, 173740); Atlantic salmon, farmed, cooked (SR Legacy, 175168); lentils, cooked (SR Legacy, 172421); black beans, cooked (SR Legacy, 173735); banana, ripe (Foundation Foods, 1105314); broccoli, boiled (SR Legacy, 169967); yogurt, plain, low-fat (SR Legacy, 170886); orange juice, not from concentrate, not fortified (Foundation Foods, 2003597). Adequate Intakes from the US National Academies, via the NIH Office of Dietary Supplements. % Daily Values use the FDA’s current Daily Value of 4,700mg.