Sodium, potassium and blood pressure: the balance that matters

When clients come to me worried about their blood pressure, the conversation almost always starts with salt. That's a sensible place to begin, but it's only half the story. Blood pressure is governed by a balance between two minerals: sodium, which we tend to eat far too much of, and potassium, which most of us don't get nearly enough of.

Why blood pressure is worth your attention

High blood pressure is often called the "silent" risk factor because it rarely causes symptoms, yet it quietly drives much of the world's burden of stroke, heart attack and kidney disease. The encouraging news is that blood pressure is remarkably responsive to what we eat, so I treat the dinner plate as a genuine part of cardiovascular care — alongside, not instead of, anything your doctor prescribes.

The sodium story: too much, and mostly hidden

Reducing salt genuinely lowers blood pressure. A Cochrane systematic review and meta-analysis found that a modest, longer-term cut in salt intake reduced systolic blood pressure by around 4.2 mmHg and diastolic by about 2.1 mmHg, with larger falls in people who already have hypertension.^[1] Here's what surprises people: the salt you can see is rarely the problem. When researchers tracked where sodium actually comes from, they found roughly 70% was already present in commercially processed and restaurant foods before it reached the table.^[2] Bread, processed meats, sauces, stocks and packaged snacks are the quiet heavyweights — you can't fix this with the salt shaker alone.

The mineral we forget: potassium

If sodium tends to raise blood pressure, potassium helps bring it down, partly by helping the kidneys excrete sodium and by relaxing blood-vessel walls. A large systematic review and meta-analysis in the BMJ found that increasing potassium reduced systolic blood pressure by about 3.5 mmHg in adults, with the benefit concentrated in those with hypertension, and higher intake associated with a 24% lower risk of stroke — with no adverse effect on kidney function in people with normal kidneys.^[3] This is why I encourage thinking about the sodium-to-potassium ratio, not sodium alone.

What a balanced pattern looks like: the DASH evidence

The clearest demonstration comes from the landmark DASH-Sodium trial in the New England Journal of Medicine. A dietary pattern rich in vegetables, fruit, legumes, nuts and low-fat dairy (naturally high in potassium, lower in sodium) lowered blood pressure; combining it with sodium reduction produced the largest reductions, especially in people with hypertension.^[4] It isn't sodium or potassium — it's the whole pattern working together.

Salt substitutes: a clever lever for some

One elegant approach is a potassium-enriched salt substitute. The Salt Substitute and Stroke Study (SSaSS), in over 20,000 people with a history of stroke or high blood pressure, found that replacing regular salt with a substitute reduced rates of stroke, major cardiovascular events and death.^[5] But these substitutes are not for everyone.

An essential safety note

Potassium is a "more is better" mineral only when your kidneys and medications allow it. If you have chronic kidney disease, or take certain blood-pressure medicines (ACE inhibitors, ARBs or potassium-sparing diuretics), deliberately increasing potassium — including via salt substitutes — can push blood potassium to dangerous levels. Please check with your GP, kidney specialist or dietitian first.

Practical steps

• Cook from scratch more often — the single most effective way to cut hidden sodium.^[2]
• Crowd the plate with potassium-rich plants — leafy greens, beans, lentils, potatoes, tomatoes, banana, avocado and yoghurt.^[3][4]
• Read the label, not the shaker — favour lower-sodium products.
• Consider a potassium-enriched salt substitute if your doctor confirms it's safe for you.^[5]

References

1. He FJ, Li J, MacGregor GA. Effect of longer term modest salt reduction on blood pressure: Cochrane systematic review and meta-analysis of randomised trials. BMJ. 2013;346:f1325. PubMed
2. Harnack LJ, Cogswell ME, Shikany JM, et al. Sources of Sodium in US Adults From 3 Geographic Regions. Circulation. 2017;135(19):1775-1783. PubMed
3. Aburto NJ, Hanson S, Gutierrez H, Hooper L, Elliott P, Cappuccio FP. Effect of increased potassium intake on cardiovascular risk factors and disease: systematic review and meta-analyses. BMJ. 2013;346:f1378. PubMed
4. Sacks FM, Svetkey LP, Vollmer WM, et al. Effects on blood pressure of reduced dietary sodium and the Dietary Approaches to Stop Hypertension (DASH) diet. N Engl J Med. 2001;344(1):3-10. PubMed
5. Neal B, Wu Y, Feng X, et al. Effect of Salt Substitution on Cardiovascular Events and Death. N Engl J Med. 2021;385(12):1067-1077. PubMed