One study review found that eating an extra two to three servings of fruit or vegetables per day – which are high in potassium – was beneficial.
A lower salt intake would increase the benefits further, researchers said.
A stroke charity said a healthy diet was key to keeping stroke risk down.
While the increase of potassium in diets was found to have a positive effect on blood pressure, it was also discovered to have no adverse effects on kidney function or hormone levels, the research concluded.
As a result, the World Health Organisation has issued its first guidelines on potassium intake, recommending that adults should consume more than 4g of potassium (or 90 to 100mmol) per day.
The BMJ study on the effects of potassium intake, produced by scientists from the UN World Food Programme, Imperial College London and Warwick Medical School, among others, looked at 22 controlled trials and another 11 studies involving more than 128,000 healthy participants.
The results showed that increasing potassium in the diet to 3-4g a day reduced blood pressure in adults.
This increased level of potassium intake was also linked to a 24% lower risk of stroke in those adults.
Researchers said potassium could have benefits for children’s blood pressure too, but more data was needed.
Salt solution
A separate study on salt intake, led by researchers at the Wolfson Institute of Preventive Medicine, Queen Mary, University of London, analysed the results of 34 previous trials involving more than 3,000 people.
It found that a modest reduction in salt intake for four or more weeks caused significant falls in blood pressure in people with both raised and normal blood pressure. This happened in both men and women, irrespective of ethnic group.
Lower blood pressure levels are known to reduce the risk of stroke and heart disease.
Graham MacGregor, professor of cardiovascular medicine at Queen Mary, who led the study, said that the “modest reduction” in salt intake was equivalent to halving the amount of salt we consume each day.
“In the UK on average our dietary salt intake is 9.5g, so we are talking about bringing this down to 6g, or if you’re very careful you can get it down to the recommended 5g – but it’s very difficult because of the amount of salt already in the food we buy.
“Bread is the biggest source of salt in our diet.”
Long-term target
He added that a further reduction in salt intake to 3g per day would have a greater effect on blood pressure and should become the long-term target for population salt intake.
Getting people to eat more fruit and vegetables containing potassium was equally important, he said.
“Salt and potassium work in opposing ways. So a combination of lower salt and higher potassium in our diets has a bigger effect than changing just one of those factors alone.”
Clare Walton, research communications officer at the Stroke Association, said high blood pressure was the single biggest risk factor for stroke.
“We know that making changes to your diet can go a long way to keeping your blood pressure under control.
“This research suggests that reducing your salt intake and eating more potassium-rich foods such as bananas, dates and spinach could reduce blood pressure and keep your risk of stroke down.”
The World Health Organisation recommends that adults should not consume more than 5g of salt a day (about one teaspoon).
The UK National Institute for Health and Care Excellence (NICE) recommends that salt intake should be reduced to 3g a day in the UK adult population by 2025.