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Potassium: The Blood Pressure Mineral Most People Miss

8 min read

High blood pressure is common among UK adults, and almost all of the dietary advice points to one thing: cut the salt. Potassium is the other half of that story, and it gets far less attention. This mineral works against sodium inside the body, helping the kidneys clear it and easing the tension in the walls of your arteries.

The average British plate is heavy on sodium from processed food and light on potassium from fruit and vegetables. The evidence that shifting this balance matters is unusually strong for a nutrition topic. Some trials measured blood pressure directly. One trial of 20,995 people went further and tracked strokes and deaths for almost five years. The findings are consistent. Here is what the research shows, how much potassium you need, and where to get it.

14%
Lower stroke rate with a potassium salt substitute
SSaSS trial (NEJM, 2021)
3.5
mmHg lower systolic blood pressure, pooled across adults
Aburto meta-analysis (BMJ, 2013)
3,500
mg of potassium a day for adults, from food
NHS guidance for adults
12%
Lower death rate over 4.7 years with the salt substitute
SSaSS trial (NEJM, 2021)

How potassium lowers blood pressure

Sodium and potassium pull in opposite directions. The first holds water in the bloodstream, which raises the volume and the pressure pushing against your artery walls. Potassium helps the kidneys pass sodium out in the urine and relaxes the smooth muscle lining the blood vessels, so the pressure eases. That is why the balance between the two matters as much as the amount of either one.

Modern diets have tilted that ratio the wrong way. Processed and packaged food loads the plate with sodium, while fruit, vegetables and beans, the main potassium sources, are often crowded out. The World Health Organization points to this imbalance as a reason to raise potassium from food, and it recommends at least 90 mmol a day, which is about 3,510 mg. The NHS sets a similar target of 3,500 mg a day for adults aged 19 to 64. Many people fall short of it.

What the blood pressure trials found

The clearest read on blood pressure comes from a WHO-commissioned review by Aburto and colleagues, published in the BMJ in 2013. It pooled 22 randomised controlled trials covering 1,606 adults. Higher potassium intake lowered systolic pressure by about 3.5 mmHg and diastolic pressure by about 2.0 mmHg. That reduction appeared in people with high blood pressure, and not in those whose pressure was already normal. In the trials where intake reached 90 to 120 mmol a day, the systolic drop was larger, around 7 mmHg, though that estimate was less certain.

Blood pressure drop with more potassiumPooled across adults, millimetres of mercury (mmHg)Systolic3.5 mmHg lowerDiastolic2.0 mmHg lowerPooled effect across 22 randomised trials
Source: Aburto NJ and colleagues, BMJ, 2013. Pooled across adults; the fall concentrated in those with hypertension.

The same review looked at longer outcomes from 11 cohort studies covering more than 127,000 people. Higher potassium intake was linked to a 24 percent lower risk of stroke. That figure comes from observational cohorts, which track associations rather than prove cause, so the open question was whether a deliberate change would do the same. Links with overall cardiovascular disease and coronary heart disease pointed the same way but did not reach statistical significance, so stroke is where the signal was strongest.

The trial that tracked strokes and deaths

Lower blood pressure is useful only if it prevents real events. The Salt Substitute and Stroke Study, led by Neal and colleagues and published in the New England Journal of Medicine in 2021, tested exactly that. It enrolled 20,995 adults across 600 villages in rural China, all of whom had a history of stroke or were aged 60 or older with raised blood pressure. Half the villages replaced ordinary table salt with a substitute made of 75 percent sodium chloride and 25 percent potassium chloride. The rest carried on with regular salt.

Over almost five years, swapping a quarter of the salt for potassium cut the rate of stroke by 14 percent, major cardiovascular events by 13 percent, and death from any cause by 12 percent.
Fewer strokes, CV events and deathsReduction with a potassium salt substitute, percent lower rate14%Stroke13%CV events12%Death20,995 adults, mean follow-up 4.7 years
Source: Neal B and colleagues (SSaSS), New England Journal of Medicine, 2021.

The safety result was reassuring. Serious problems from high blood potassium, the main worry with this approach, occurred at a similar rate in both groups. This was a food-level swap in a high-risk, older population, so it does not prove the same benefit in younger, healthy people. It does show that nudging the sodium-to-potassium ratio at the dinner table can change hard outcomes, not just numbers on a monitor.

Who this helps, and who should be careful

The blood pressure benefit concentrates in people who already have raised pressure. In the BMJ review, those with normal pressure saw little change, so more potassium is not a reason to expect a lower reading if yours is already healthy. The effect is also larger when sodium intake is high, which fits the idea that potassium is working against that excess.

There is an important exception. The kidneys clear potassium from the blood, so anyone with reduced kidney function can build up dangerous levels. People with chronic kidney disease, and anyone taking medicines that raise potassium such as ACE inhibitors, angiotensin receptor blockers or potassium-sparing diuretics, should not load up on potassium or switch to a salt substitute without medical advice. The NHS also advises that older people avoid potassium supplements unless a doctor recommends them, because ageing kidneys clear it less well. For most other people, getting potassium from food rather than pills keeps intake in a safe range.

How to get more potassium

Food is the sensible route, and the choices are ordinary. The NHS lists bananas, vegetables such as broccoli, parsnips and Brussels sprouts, beans and pulses, nuts and seeds, fish, and lean meat as good sources. Build meals around these rather than relying on one food.

1. Fill half the plate with vegetables and pulses
Beans, pulses, broccoli and fish all carry useful amounts, and a varied plate reaches the 3,500 mg target more easily than any single food.
2. Cut the sodium at the same time
Most sodium hides in bread, processed meat, sauces and ready meals. Eating less of it shifts the sodium-to-potassium ratio from both sides at once.
3. Consider a potassium salt substitute
A substitute that replaces part of the sodium with potassium is the swap tested in the 2021 trial. Use it only if your kidneys are healthy and your doctor is content with it.
4. Keep it from food, not supplements
Whole foods deliver potassium alongside fibre and other nutrients, and it is hard to take in too much from food alone. Potassium pills are a medical decision, not a casual habit.

Common mistakes

The first is treating bananas as the whole answer. One banana provides useful potassium, but it is a small share of the daily target, and vegetables, beans and fish do more of the work across a day. The second is chasing potassium while ignoring sodium, which leaves the ratio barely changed. The third is reaching for supplements to hit a number quickly. That is where the risk of excess sits, and it is the one route the NHS flags for caution.

Frequently asked questions

Does potassium help if my blood pressure is already normal?
Probably not much. In the BMJ review, the fall in pressure showed up in people with hypertension, not in those with normal readings. It also works harder when sodium intake is high, so the benefit is largest for people eating a salty, low-potassium diet.
How much potassium do I need a day?
The NHS sets 3,500 mg a day for adults aged 19 to 64, and the World Health Organization suggests at least 3,510 mg. Both expect you to reach it from food rather than supplements.
Are potassium salt substitutes safe?
In the 2021 SSaSS trial, serious high-potassium events were no more common with the substitute than with regular salt in the population studied. Salt substitutes are not suitable for some people, though. Anyone with kidney disease or on potassium-raising medicines should check with a doctor first.
Which foods have the most potassium?
The NHS names bananas, broccoli, parsnips, Brussels sprouts, beans and pulses, nuts and seeds, fish, and lean meat. Variety across these beats leaning on one food.
Should I take a potassium supplement for my blood pressure?
For most people the answer is to use food, not pills. Supplements carry a real risk of excess, the NHS advises older adults to avoid them unless told otherwise, and the trial evidence is built on food-level intake. Treat supplements as a medical decision.

The bottom line

Potassium is an overlooked lever in blood pressure control. Across randomised trials it lowered pressure in people with hypertension, and in a 20,995-person trial a potassium salt substitute cut strokes and deaths over almost five years. The practical move is the familiar one: more vegetables, beans and whole foods, and less processed salt. Keep potassium coming from your plate, and if you have kidney trouble or take blood pressure medicines, make any salt-substitute change a conversation with your doctor.

Want your nutrition built around real evidence?
DT Fitness London builds personal training and nutrition plans on the research, not on headlines. Book a consultation at www.dtfitnesslondon.com and we will set targets that fit your health and your week.

Sources

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