A study involving scientists from Imperial College London found those who ate higher amounts of salt had higher blood pressure – no matter how healthy their overall diet.
They warned their findings suggest people should monitor their salt intake, while food manufacturers should lower the salt content in their products.
High blood pressure affects more than one in four adults in the UK, and increases the risk of a number of conditions including heart attacks and stroke. It is thought to have a number of causes, including age, weight and eating too much salt.
It was thought the vitamins and minerals in fruit and vegetables might in some way affect blood vessels, enabling them to lower blood pressure, and that eating high amounts of fruit and vegetables might help counteract the effect of high salt on blood pressure.
However, while these foods do tend to lower blood pressure, the new research suggests they do not counteract the adverse influence of salt intake.
The study, which is published in the journal Hypertension, analysed the diets of more than 4,000 people from the US, UK, Japan and China using data from the INTERMAP study.
The team assessed concentrations of sodium and potassium in the participants’ urine samples, while they assessed their intake of more than 80 nutrients that may be linked to low blood pressure, including vitamin C, fibre, and omega-3 fatty acids.
The researchers found a correlation between high blood pressure and higher salt intake, even in people who were eating a high amount of potassium and other nutrients. The researchers estimated salt intake by analysing sodium in the urine, as well as analysing dietary data.
The recommended upper limit of adult salt intake in the UK is 6g a day – around one teaspoon.
The study found that average salt intake across the study was 10.7g a day. The average intake for the UK was 8.5g, while the intake for the USA, China and Japan were 9.6g, 13.4g and 11.7g respectively.
Increasing salt intake above this average amount was linked to an increase in blood pressure. An increase of an additional 7g (1.2 teaspoons) of salt above the average intake was associated with an increase in systolic blood pressure of 3.7 mmHg.
Joint lead author Dr Queenie Chan, from Imperial College London’s School of Public Health, said the research shows the importance of reducing salt intake.
She said: “We currently have a global epidemic of high salt intake – and high blood pressure.
“This research shows there are no cheats when it comes to reducing blood pressure. Having a low salt diet is key – even if your diet is otherwise healthy and balanced.
“As a large amount of the salt in our diet comes from processed food, we are urging food manufacturers to take steps to reduce salt in their products.”
Scientists acknowledged that because the data was collected over only four days, it provides information from a snapshot of time.
They said they now hope to focus on longer term studies involving a greater number of people.