Potassium

Potassium is the main positively charged ion inside cells. It works in close partnership with sodium (the main one outside cells) to keep fluid balance steady, conduct nerve signals, and pace muscle contractions, including the heartbeat. Higher dietary potassium intake is associated with lower blood pressure in the general population, and the NHS Eatwell Guide leans on this when it nudges people towards more fruit, vegetables, pulses, and unprocessed staples.

The reason most UK adults are short is structural. Potassium tracks the plant-food and unprocessed-food parts of the diet. When the bulk of calories come from refined and processed foods (which have had potassium-rich potato skin, bran, and bean liquor stripped or never included) intake drops well below the 3,500mg reference. The fix is the same fix recommended for fibre and for blood pressure: more potatoes, beans and lentils, leafy greens, fruit, and fish.

Sodium and potassium are also in a tug of war for blood-pressure control. UK shoppers eat too much sodium (salt) and too little potassium. Closing one half of the gap helps the other, which is why dietary advice for blood pressure pairs less salt with more potassium-rich food.

Potassium is in a wide range of foods, but it concentrates in unprocessed plant foods (potatoes with the skin, pulses, leafy greens, fruit), oily fish, and dairy. Values per 100g come from USDA SR Legacy and McCance and Widdowson 7th edition; the site's food entries currently store macros only, so the per-nutrient values here are from those reference datasets. Percentages of the adult RNI use 3,500mg as the basis.

Practical: a baked jacket potato is one of the most efficient potassium meals on a UK budget. Most of the potassium sits in and just under the skin, so eating the skin is the point.

The UK Reference Nutrient Intake (RNI) for potassium is set by SACN (1991 Dietary Reference Values). Values are mg per day.

Low dietary potassium is common in UK adults but rarely shows as classic deficiency signs from food alone. True clinical low potassium in the blood (hypokalaemia) is more commonly caused by other things: persistent vomiting or diarrhoea, certain water tablets (diuretics), eating disorders, or the use of laxatives. When it does occur, signs include:

• Muscle weakness or cramps
• Constipation
• Fatigue
• An irregular heartbeat (palpitations) in severe cases

If you have persistent vomiting, diarrhoea, or use water tablets and notice these symptoms, see a GP. A simple blood test gives a clear answer.

The bigger UK story is dietary shortfall, not clinical deficiency. Most adults sit below the 3,500mg reference for a long-running reason: not enough plant food and too many processed staples. The cardiovascular consequence is small per day but cumulative over years.

Potassium from food is not a realistic risk for the general population. The issue is supplements, and certain medical conditions.

NHS supplement guidance: taking 3,700mg or less of potassium supplements a day is unlikely to have obvious harmful effects. Higher doses can cause stomach pain, nausea, and diarrhoea.

People who need to limit potassium (do not follow the general advice on this page):

• Chronic kidney disease, particularly later stages and dialysis. Damaged kidneys cannot clear excess potassium, and a high intake risks dangerous blood levels.
• People on potassium-sparing diuretics (such as spironolactone or amiloride), ACE inhibitors, or angiotensin-receptor blockers (ARBs), especially if combined.
• Some types of heart failure where serum potassium is being monitored.

If you are in one of these groups, your kidney team, cardiologist, or GP gives you the right intake for your situation. Renal dietitians provide personalised "foods to limit" lists that take into account portion size and how you cook (for example boiling and discarding the cooking water reduces the potassium in potatoes).

Potassium supplements are not recommended for the general UK population. The NHS line is clear: get potassium from food.

• Most UK adults can close the gap to 3,500mg by eating more potatoes (with the skin), pulses, leafy greens, fruit, and unprocessed staples.
• If you are taking water tablets, ACE inhibitors, ARBs, or treatment for any heart or kidney condition, do not start a potassium supplement without GP advice.
• People with chronic kidney disease may be advised to take a potassium binder; that is a prescription medicine, not a food supplement, and is managed by the renal team.

The Eatwell Guide naturally lands UK adults at a reasonable potassium intake when it is actually followed: a third of the plate vegetables, a third starchy carbohydrate (potatoes count), some pulses or fish, some dairy or alternatives.

• Salt and blood pressure: Salt and sodium covers the other half of the sodium-potassium balance and the UK 6g salt target.
• What the UK official position looks like in practice: The Eatwell Guide.
• The big plant-food sources for potassium: Potato, Lentils, Spinach, Banana.

• NHS. Vitamins and minerals: Potassium. nhs.uk/conditions/vitamins-and-minerals/others. Adult RNI and supplement guidance.
• SACN. Dietary Reference Values for Food Energy and Nutrients for the United Kingdom. Department of Health Report on Health and Social Subjects 41 (1991). Source of the age-banded RNIs.
• Public Health England. McCance and Widdowson's The Composition of Foods, 7th summary edition (2015).
• USDA Agricultural Research Service. FoodData Central, SR Legacy release. fdc.nal.usda.gov.
• NHS. Chronic kidney disease: Diet advice. Reference for the renal-restriction note above.

This page is reference information for UK shoppers. It is not medical advice. People with kidney conditions or on blood-pressure medicines should follow personalised advice from their renal team or GP.