Potassium: What It Does, How Much You Need and Who Should Be Careful

Potassium is the main mineral inside your cells, where it sets the electrical charge that nerves and muscles run on. Adults need 3,500 mg a day, almost all of it from food, and healthy kidneys match what leaves to what comes in. It matters most for people whose kidneys or medicines cannot shed it.^{1, 2} This page is part of the Wellgard electrolyte guide.

Evidence at a glance

• Trials: 22 randomised trials pooled in 2013 (1,606 people) and 32 in a 2020 dose-response analysis (1,764 people); 11 cohort studies of 127,038 people for stroke.^{3, 4}
• Largest single trial: 353 adults with high-normal blood pressure, 60 mmol of potassium chloride a day for 6 months.⁵
• Strongest measured outcome: systolic pressure 3.49 mmHg lower, an effect seen in hypertension, and 7.16 mmHg lower at 90 to 120 mmol a day.³
• Not tested: the 2020 analysis's trials gave 30 to 140 mmol a day (about 1.2 to 5.5 g); none tested a 300 mg serving.⁴

Sources checked on 13 October 2026.

What does potassium do in the body?

Potassium is the most abundant charged mineral inside cells. A pump in every cell wall pushes potassium in and sodium out, and the difference across the wall is the voltage that lets nerves signal and muscles, including the heart, contract.^{2, 6} The NHS says potassium "helps control the balance of fluids in the body" and helps the heart muscle work properly.¹ Balance is held by the kidneys, which raise or lower how much they pass in urine to match intake; about 90% of the potassium you eat leaves that way, about 10% in stool and very little in sweat.^{2, 6}

Three health claims are authorised for potassium in Great Britain, each for a food or supplement providing at least 15% of the 2,000 mg reference intake, so 300 mg, per serving: "Potassium contributes to normal functioning of the nervous system", "Potassium contributes to normal muscle function" and "Potassium contributes to the maintenance of normal blood pressure".^{7, 8}

How much potassium do you need a day?

"Adults (19 to 64 years) need 3,500mg of potassium a day," says the NHS, adding that you should be able to get it all from your daily diet.¹ That is about 90 mmol. Good sources, it says, include bananas, beans and pulses, nuts and seeds, fish and meat.¹

Is one banana a day enough? No single food is: a banana gives about a tenth of the 3,500 mg. A jacket potato, a glass of milk, a salmon fillet and a banana together come to about 2,300 mg.⁹

Can potassium lower blood pressure?

In people with high blood pressure, yes, by a modest amount. A 2013 review for the World Health Organization pooled 22 trials of 1,606 people: extra potassium lowered systolic pressure by 3.49 mmHg and diastolic by 1.96 mmHg, "an effect seen in people with hypertension but not in those without". At 90 to 120 mmol a day (about 3.5 to 4.7 g) systolic pressure fell 7.16 mmHg. The authors graded this high-quality evidence, found no harm to kidney function or blood fats, and in 11 cohort studies linked higher intake with a 24% lower stroke risk (moderate quality).³

More is not always better. A 2020 analysis of 32 trials found a U-shape: the fall weakened above an extra 30 mmol a day (about 1.2 g), and above about 80 mmol (3.1 g) pressure rose again in people taking blood-pressure medicines.⁴ In the largest single trial, 353 adults with high-normal pressure took 60 mmol a day: diastolic pressure was 1.8 mmHg lower at 3 months and 0.3 mmHg at 6 months, with no significant change in systolic.⁵

Potassium contributes to the maintenance of normal blood pressure at 300 mg a serving or more; the figures above are trial figures.⁷ Any change to a blood-pressure medicine is for the prescriber.

How much potassium is too much?

The NHS says "3,700mg or less of potassium supplements a day is unlikely to have obvious harmful effects", and that too much can cause stomach pain, feeling sick and diarrhoea.¹ The serious version is hyperkalaemia, a blood potassium usually defined as 5.5 mmol/L or more against a normal range of about 3.5 to 5.0. It is often silent or vague (weakness, nausea, muscle pain, tingling) and its danger is the heart: it can cause rhythm disturbances and cardiac arrest.^{10, 11} A high result is managed by the clinician who finds it, from diet changes to medicines.¹⁰

Who should be careful with potassium?

People with chronic kidney disease, because damaged kidneys pass less potassium. The NHS says that with kidney disease "it's important to avoid taking potassium supplements".^{10, 12} Kidney teams also teach that boiling vegetables draws some potassium into the water, and that salt substitutes are a hidden source.¹⁰

People on medicines that hold potassium back: ACE inhibitors such as ramipril, angiotensin receptor blockers such as losartan, and spironolactone or amiloride. The NHS ramipril page lists spironolactone, amiloride and potassium among medicines that can increase the amount of potassium in your blood.¹³ The caution has a history: after a trial led doctors to add spironolactone to ACE inhibitors in heart failure, hyperkalaemia admissions among older Ontario patients on ACE inhibitors rose from 2.4 per 1,000 in 1994 to 11.0 in 2001.¹⁴

Older people. "Older people should not take potassium supplements unless advised to by a doctor," because ageing kidneys clear it less well.¹ If any of this applies, ask the pharmacist or the prescriber before using any potassium-containing product; the same caution sits on electrolytes, kidneys and blood pressure.

How do you read potassium on a label?

Look for potassium as the element, in milligrams, not the weight of the compound. By molecular weight, potassium chloride is about 52% potassium and potassium citrate about 36 to 38%, so 500 mg of potassium chloride supplies about 260 mg of potassium.

Food supplies most people's potassium, as the NHS says; where a formula carries 300 mg or more a serving it may say that potassium contributes to normal muscle function, and that is the line to look for.^{1, 7} For "best potassium supplement", use a checklist: potassium as the element, the 300 mg claim line, the servings a day against 3,700 mg from supplements, and the warnings printed for kidney disease and medicines. How to read an electrolyte label applies the same method to sodium and magnesium.

What we don't know

• How well the body absorbs potassium from different foods has barely been measured.⁶
• The blood-pressure rise above about 80 mmol a day rests on few high-dose trials.⁴
• Whether extra potassium lowers blood pressure without hypertension is unproven: the 2013 pooled trials found no effect there, and the largest trial's early fall had gone by 6 months.^{3, 5}
• The 24% lower stroke risk comes from cohort studies, which cannot show that potassium caused it.³

Frequently asked questions

What are the signs of low potassium?

Below the normal 3.5 mmol/L, symptoms usually appear only under about 3.0: leg cramps, weakness and constipation, and in severe cases rhythm disturbances. Common causes are prolonged vomiting or diarrhoea, laxative overuse and diuretics: a blood test diagnoses it (see signs of low potassium).¹¹

Does potassium help cramp?

Potassium contributes to normal muscle function at 300 mg a serving or more. Cramp during exercise is another matter: in 210 Ironman triathletes, the 43 who cramped had the same blood electrolytes as those who did not, and a faster pace and a history of cramp predicted it, so potassium is not a promise against cramp.^{7, 15}

Is potassium lost in sweat?

Very little. About 90% of potassium leaves in urine; sodium is the mineral sweat carries, set against the day in how much salt a day.⁶

Can you take potassium with magnesium?

Yes, with the kidney and medicine cautions above. Both have authorised wordings at 15% of their reference intakes (300 mg potassium, 56.25 mg magnesium). Low magnesium often accompanies low potassium in people on diuretics.^{7, 11} What is magnesium good for? covers magnesium.

Does potassium cause dizziness?

Dizziness is not a headline sign of low or high potassium, but both can disturb heart rhythm.^{10, 11} The NHS says call 999 for palpitations with chest pain, shortness of breath or "feeling faint or fainting".¹⁶ Otherwise, see a GP.

Sources

1. NHS. Vitamins and minerals: others. Page last reviewed 3 August 2020 (review overdue); checked 13 October 2026. nhs.uk.
2. Palmer BF. Review. Clinical Journal of the American Society of Nephrology, 2015. PubMed 24721891.
3. Aburto NJ, et al. Pooled analysis of 22 randomised trials, 1,606 people, and 11 cohort studies, 127,038 people. BMJ, 2013. PubMed 23558164.
4. Filippini T, et al. Dose-response analysis of 32 randomised trials, 1,764 people (total from the full text), each at least 4 weeks. Journal of the American Heart Association, 2020. PubMed 32500831.
5. Whelton PK, et al. Randomised trial, 353 adults with high-normal blood pressure, 6 months. Annals of Epidemiology, 1995. PubMed 7795836.
6. Stone MS, et al. Review. Nutrients, 2016. PubMed 27455317.
7. Department of Health and Social Care. Great Britain nutrition and health claims register, potassium. gov.uk.
8. Regulation (EU) No 1169/2011 as it applies in Great Britain, Annex XIII. legislation.gov.uk.
9. Public Health England. Composition of Foods Integrated Dataset (CoFID), 2021. gov.uk.
10. Sarnowski A, et al. Review; definition, symptoms and diet points from the full text. International Journal of Nephrology and Renovascular Disease, 2022. PubMed 35942480.
11. Kardalas E, et al. Review; normal range, symptoms and causes from the full text. Endocrine Connections, 2018. PubMed 29540487.
12. NHS. Chronic kidney disease: treatment. Page last reviewed 22 March 2023 (review overdue); checked 13 October 2026. nhs.uk.
13. NHS. Taking ramipril with other medicines and herbal supplements. Page last reviewed 18 March 2026. nhs.uk.
14. Juurlink DN, et al. Population time-series, more than 1.3 million adults aged 66 and over, 1994 to 2001. New England Journal of Medicine, 2004. PubMed 15295047.
15. Schwellnus MP, Drew N, Collins M. Prospective cohort, 210 Ironman triathletes. British Journal of Sports Medicine, 2011. PubMed 21148567.
16. NHS. Heart palpitations. Page last reviewed 17 March 2026. nhs.uk.

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