Potassium

What it is

Potassium is an electrolyte that helps nerves, muscles and the heart work, and balances fluid in your body. It is plentiful in bananas, potatoes, beans, spinach, yoghurt, fish and many fruits and vegetables.

Many adults get less than the recommended 3,500 mg a day. Higher potassium intake from food is linked with lower blood pressure. Supplements are marketed for cramps, blood pressure and energy.

Unlike most minerals, potassium has a real risk of causing harm quickly at high doses, because it directly affects heart rhythm.

How it works

Potassium sits mainly inside cells and works with sodium to create the electrical charge that nerves and muscles use. The kidneys keep blood potassium in a narrow range. If the kidneys can not clear it, levels rise and can trigger dangerous heart rhythms.

What the evidence says

• Strong Correcting low potassium (hypokalaemia)
  Usually prescribed and monitored by doctors after blood tests, for example with diuretics or after severe diarrhoea.
• Moderate Lower blood pressure (dietary potassium)
  Eating more potassium-rich foods, or switching to lower-sodium salt substitutes, modestly lowers pressure for many; tablets are less well studied.
• Weak Muscle cramps
  Cramps are rarely due to low potassium in healthy people.
• Moderate Kidney stone prevention (potassium citrate)
  Prescribed for particular stone types, under medical supervision.
• Limited Exercise performance
  Replaced through normal food and fluids; no benefit from extra tablets.

Evidence ratings are our plain-English summary of how much good human research exists, not a promise of results. How we rate evidence.

Dosage and timing

• Most people should get potassium from food rather than tablets.
• Over-the-counter products in the UK are usually low dose; higher-dose products are prescription only.
• Take with plenty of water and a meal to reduce stomach irritation.
• Do not use potassium-based salt substitutes liberally if you take certain blood pressure medicines or have kidney disease.

Forms and what to look for

• Potassium chloride: common in prescribed products and salt substitutes; can irritate the stomach.
• Potassium citrate: used for urinary stones and acidity.
• Potassium gluconate: gentle, low dose, found in supplements.
• Electrolyte mixes: contain small to moderate amounts; read the label.
• Whole foods: bananas, beans, potatoes and leafy greens do most of the job.

What to expect, and when

• If you were genuinely low, muscle weakness and cramps ease within days under medical care.
• For blood pressure, diet changes take weeks to show.
• You will not feel energy changes in healthy people.

Side effects

• Nausea, vomiting, stomach pain
• Diarrhoea
• Throat or bowel irritation or ulcers from solid tablets
• High potassium: muscle weakness, tingling, irregular heartbeat, palpitations, cardiac arrest

Interactions

• ACE inhibitors, ARBs, spironolactone, eplerenone and other potassium-sparing drugs can raise potassium
• NSAIDs such as ibuprofen can reduce potassium clearance
• Trimethoprim, heparin and some immunosuppressants raise potassium
• Digoxin: both low and high potassium affect risk

Who should avoid it

• Anyone with kidney disease
• People taking ACE inhibitors, ARBs or potassium-sparing diuretics
• People with heart rhythm problems or adrenal conditions
• Anyone with diabetes complications affecting kidneys, unless supervised

Risks and safety

• Hyperkalaemia can cause life-threatening heart rhythm disturbances, sometimes with little warning.
• High-dose potassium is prescription only in the UK for this reason.
• Not a WADA-prohibited substance.
• Salt substitutes (potassium chloride) are a hidden source for people on interacting medicines.

Buying well: quality and testing

• Stick with reputable brands that list mg per serving.
• Avoid imported high-dose products.
• Read electrolyte mix labels for potassium content.
• If a doctor prescribes potassium, follow the exact instructions.

Bottom line

For most people, more fruit, veg, beans and potatoes is the best way to boost potassium. Supplements are for medical situations; if you have kidney problems or take blood pressure tablets, check with a clinician before adding any.