Potassium

Potassium is the main intracellular cation. It maintains membrane potential, drives the Na⁺/K⁺-ATPase pump that keeps cells alive, and is required for muscle contraction and cardiac rhythm. Chronic intake shortfalls are one of the largest population-scale nutrient problems in the developed world; acute derangements are life-threatening.

Daily requirements

• Adult men (IOM AI): 3,400 mg/day.
• Adult women (IOM AI): 2,600 mg/day.
• DASH-diet target for blood pressure: ~4,700 mg/day.
• Actual US intake (median): ~2,300 mg/day — well below the AI for both sexes.
• No IOM upper limit for healthy adults — but supplements over 99 mg per dose require prescription in the US because of hyperkalaemia risk.

Blood pressure — the DASH evidence

The DASH-Sodium trial demonstrated that raising dietary potassium (via fruits, vegetables, and low-fat dairy) while cutting sodium reduces systolic BP by 8–14 mm Hg in hypertensive adults — larger than most single antihypertensive drugs. The 2021 Chinese SSaSS trial showed KCl-based salt substitute (75% NaCl / 25% KCl) reduced stroke, cardiovascular events, and death in 21,000 rural adults over 5 years.

The banana myth

A medium banana has 422 mg potassium — respectable, but not exceptional. A baked potato with skin has 926 mg. A cup of white beans has 1,189 mg. Bananas are famous for potassium mostly because they were the food doctors could dependably recommend to K-deficient hospital patients decades ago; they're not the densest source.

Hyperkalaemia — when potassium becomes dangerous

Serum potassium above 5.5 mmol/L causes peaked T waves on ECG; above 6.5 mmol/L causes broadened QRS and risk of ventricular fibrillation. Groups who should NOT freely increase potassium intake or use salt substitutes:

• Chronic kidney disease stage 3B or worse (eGFR < 45)
• Anyone on an ACE inhibitor, ARB, or ARNI (sacubitril/valsartan)
• Anyone on spironolactone, eplerenone, amiloride, or triamterene
• Type 4 renal tubular acidosis, Addison's disease, hypoaldosteronism

High-potassium foods

• Baked potato with skin (1 medium): 926 mg
• White beans (1 cup cooked): 1,189 mg
• Lentils (1 cup cooked): 731 mg
• Cooked spinach (1 cup): 839 mg
• Sweet potato (1 medium baked): 542 mg
• Salmon (3 oz): 534 mg
• Avocado (½ fruit): 487 mg
• Banana (1 medium): 422 mg
• Yoghurt (1 cup plain): 380 mg
• Coconut water (1 cup): 600 mg