Potassium is an electrolyte that keeps your cells, nerves, and muscles working properly. It’s the most abundant positively charged ion inside your cells, concentrated about 35 times higher there than in your blood. That steep difference across cell membranes is what allows your nerves to fire, your heart to beat rhythmically, and your muscles to contract on command. Most adults need between 2,600 and 3,400 mg per day, and falling short affects everything from energy levels to heart rhythm.
How Potassium Powers Your Cells
Nearly every cell in your body contains a tiny pump that constantly shuttles sodium out and potassium in. This pump uses energy to move three sodium ions out for every two potassium ions it pulls in, creating an electrical charge across the cell membrane. That charge, roughly negative 95 millivolts at rest, is like a loaded spring. When a nerve signal arrives or a muscle needs to contract, the cell releases that stored charge in a rapid burst called an action potential.
Without enough potassium to maintain this gradient, cells in excitable tissues like nerves and muscles can’t reset after firing. The result is weakness, cramping, and in severe cases, paralysis. Your body treats potassium levels in the blood as a tightly controlled priority, keeping them between 3.5 and 5.0 mmol/L at all times.
Potassium and Your Heart
Your heart is especially sensitive to potassium levels. The negative resting charge that potassium creates in heart muscle cells keeps them stable between beats, preventing them from firing prematurely. When blood potassium drops too low, this stabilizing effect weakens. Heart cells become more excitable, calcium builds up inside them, and the risk of dangerous irregular rhythms climbs. Low potassium can trigger a type of rapid, chaotic heartbeat that, in the worst case, leads to cardiac arrest.
Too much potassium is equally dangerous for the heart. As levels rise above 5.5 mmol/L, the electrical signals that coordinate each heartbeat start to distort. At levels between 6.5 and 7.5 mmol/L, the signal that triggers each heartbeat can disappear entirely. Above 8.0 mmol/L, the heart’s electrical activity becomes severely disorganized, and cardiac arrest can follow quickly. The mortality rate for severe, untreated high potassium approaches two-thirds.
Blood Pressure and Stroke Risk
Potassium works in direct opposition to sodium when it comes to blood pressure. Sodium pulls water into your blood vessels, raising pressure. Potassium helps your body flush excess sodium and relaxes blood vessel walls. The CDC notes that consuming too much sodium and too little potassium raises blood pressure, and that increasing potassium intake can lower blood pressure in people with hypertension. That reduction in blood pressure also lowers the risk of heart disease and stroke.
This is one reason diets rich in fruits and vegetables, like the DASH eating plan, are consistently linked to better cardiovascular health. These foods are naturally high in potassium and low in sodium, shifting the balance in a favorable direction.
How Your Kidneys Control Potassium
Your kidneys are the main regulators of potassium balance. They adjust how much potassium you excrete based on signals from a hormone called aldosterone, produced by your adrenal glands. When potassium levels rise, aldosterone increases. It acts on the filtering tubes in your kidneys in three ways: it activates pumps that pull more potassium into kidney cells, it increases sodium reabsorption to create an electrical gradient that drives potassium out into your urine, and it makes kidney cell membranes more permeable to potassium so more of it can pass through.
This system works well in healthy kidneys, but kidney disease impairs potassium excretion. People with reduced kidney function can accumulate potassium to dangerous levels, which is why recommended intake guidelines don’t apply to them without medical guidance.
Bone Health and Calcium Retention
Potassium plays a less obvious but meaningful role in keeping bones strong. The typical Western diet, heavy in meat and refined grains, generates a mild but chronic acid load in the body. To buffer that acidity, the body draws alkaline minerals from bone, gradually weakening it over time. Potassium-rich foods, particularly fruits and vegetables, supply alkaline salts that neutralize this acid without pulling from bone stores.
Potassium also helps your kidneys hold onto calcium rather than excreting it. Studies have found that potassium bicarbonate reduces urinary calcium loss in healthy men, and potassium citrate does the same in men with kidney stones. Research in older Korean adults found that women with the highest potassium intake had significantly greater bone mineral density at the hip and spine compared to those with the lowest intake. Postmenopausal women in the highest intake group had a 32% lower risk of osteoporosis at the lumbar spine.
Signs of Low Potassium
Mild low potassium (3.0 to 3.5 mmol/L) often produces no obvious symptoms. As levels drop below 3.0 mmol/L, you may notice muscle weakness, cramps, fatigue, heart palpitations, constipation, or abdominal discomfort. Below 2.5 mmol/L, significant muscle weakness sets in, and the risk of life-threatening heart rhythm problems and respiratory muscle paralysis rises sharply. Common causes include prolonged vomiting or diarrhea, heavy sweating, and certain medications like diuretics.
Signs of High Potassium
Mild elevations above 5.0 mmol/L are often silent. Symptoms typically appear above 6.0 mmol/L and include muscle weakness, tingling, and nausea. The most serious concern is the effect on heart rhythm: progressive electrical changes show up on an electrocardiogram as potassium rises, starting with tall, peaked T waves and potentially ending in cardiac arrest at very high levels. High potassium most commonly affects people with kidney disease, those on certain blood pressure medications, or people taking potassium supplements inappropriately.
How Much You Need
The adequate daily intake for adult men (ages 19 and older) is 3,400 mg. For adult women, it’s 2,600 mg, rising to 2,900 mg during pregnancy and 2,800 mg during breastfeeding. Children’s needs range from 2,000 mg at ages 1 to 3 up to 2,300 to 3,000 mg during adolescence. Most people in Western countries fall short of these targets.
Best Food Sources of Potassium
Bananas get the most attention, but they’re far from the richest source. A medium baked potato with the skin delivers 919 mg, more than double the 362 mg in a small banana. A small baked salmon fillet provides 763 mg, and a half cup of cooked spinach offers 591 mg. Other strong sources include:
- Cantaloupe: 417 mg per cup
- Low-fat milk: 388 mg per cup
- Pinto beans: 373 mg per half cup
- Chicken breast: 359 mg per medium piece
- Edamame: 338 mg per half cup
- Baby carrots: 320 mg per 10 carrots
- Raisins: 270 mg per quarter cup
- Broccoli: 268 mg per half cup, cooked
- Orange: 237 mg per medium fruit
A diet built around whole fruits, vegetables, beans, dairy, and fish can easily meet the daily target without supplements. Over-the-counter potassium supplements are intentionally limited to small doses because large amounts taken at once can spike blood levels dangerously. For most people, food is the safest and most effective way to get enough.