Potassium and blood pressure: what the trial evidence actually shows

Increasing potassium intake reliably lowers blood pressure in people who already have hypertension — by around 3 to 7 mm Hg systolic depending on the dose — but does little for those whose pressure is already normal [s2]. In the one large randomised trial to follow this through to hard outcomes, swapping ordinary table salt for a potassium-enriched substitute cut the rate of stroke, major cardiovascular events and death, which is the strongest evidence yet that the effect is real and worth having [s3].

The blood-pressure effect, and its size

The World Health Organization recommends increasing potassium intake from food to help control blood pressure and reduce cardiovascular risk in adults, a recommendation built on the same pooled trial evidence [s1]. The quantitative backbone is a 2013 systematic review that meta-analysed 22 randomised controlled trials in 1,606 adults [s2]. Higher potassium intake reduced systolic blood pressure by 3.49 mm Hg (95% confidence interval 1.82 to 5.15) and diastolic pressure by 1.96 mm Hg (0.86 to 3.06), an effect seen in people with hypertension but not in those without it [s2]. The reduction was larger where intake reached 90 to 120 mmol a day — a systolic fall of 7.16 mm Hg (1.91 to 12.41) — with no clear dose-response beyond that [s2].

Crucially, the same review found no evidence that higher potassium harmed kidney function, blood lipids or catecholamine concentrations in adults, which addresses a common worry about pushing intake up [s2]. In children, three controlled trials and one cohort study suggested a non-significant systolic reduction of 0.28 mm Hg, so the paediatric case is not made [s2].

From pressure to actual events

A number on a cuff is a surrogate; what a reader wants to know is whether more potassium prevents strokes and deaths. On the observational side the 2013 review already pointed that way, linking higher potassium intake to a 24% lower risk of incident stroke (risk ratio 0.76, 0.66 to 0.89), while associations with overall cardiovascular disease (0.88, 0.70 to 1.11) and coronary heart disease (0.96, 0.78 to 1.19) were not statistically significant [s2].

The Salt Substitution and Stroke Study (SSaSS) then tested it head-on. This open-label trial randomised 600 villages in rural China — 20,995 people with a history of stroke or who were 60 or older with high blood pressure — to a salt substitute of 75% sodium chloride and 25% potassium chloride, or to regular salt [s3]. Over a mean 4.74 years, the rate of stroke was 29.14 events per 1,000 person-years with the substitute against 33.65 with regular salt (rate ratio 0.86; 95% confidence interval 0.77 to 0.96) [s3]. Major cardiovascular events fell from 56.29 to 49.09 per 1,000 person-years (rate ratio 0.87; 0.80 to 0.94), and death from any cause from 44.61 to 39.28 (rate ratio 0.88; 0.82 to 0.95) [s3]. The substitute is a two-way intervention — more potassium and less sodium at once — so it does not isolate potassium, but as a real-world swap it is exactly the change most people would make.

The safety line that matters

Potassium is not a free lunch for everyone. The kidneys clear excess potassium, so people with chronic kidney disease, or on medicines such as ACE inhibitors, ARBs or potassium-sparing diuretics that limit its excretion, can accumulate it to dangerous levels — hyperkalaemia, which can disturb heart rhythm. SSaSS is reassuring here but with a caveat: the rate of serious adverse events attributed to hyperkalaemia was not significantly higher with the substitute than with regular salt (3.35 versus 3.30 per 1,000 person-years; rate ratio 1.04; 0.80 to 1.37) [s3]. The reassurance applies to a general older population; it was not a trial of people with advanced kidney disease, for whom potassium-enriched salt can be the wrong choice.

How to read this

The honest summary is a real but conditional benefit. More dietary potassium lowers blood pressure meaningfully in people who have hypertension, barely moves it in those who do not, and — in the form of a potassium-for-sodium salt swap — has now been shown to cut strokes and deaths in a large trial [s2][s3]. The one group who should not act on this without medical advice are people with impaired kidney handling of potassium [s3]. This sits alongside the sodium side of the same equation, the dietary pattern with the best trial record for blood pressure, the DASH diet, the question of what counts as high blood pressure, and the salt-and-kidney-disease evidence.

This article is informational and not dietary or medical advice; decisions about potassium intake, salt substitutes or blood-pressure treatment — especially with any kidney condition — should be made with a qualified clinician.