Healthy diet 'doesn't protect against too much salt'
Eating plenty of fruit and vegetables does not prevent heart attacks and strokes triggered by salt, according to new research.
It was thought healthy foods in some way protected the cardiovascular system against the damage too much of the seasoning can cause.
But a study of more than 4,600 people has found those with high salt intake had higher blood pressure - irrespective of the rest of their diet.
Joint lead author Dr Queenie Chan, of Imperial College London, 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."
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 believed to have a number of causes including age, weight and eating too much salt.
Dr Chan and colleagues, whose findings are published in Hypertension, are now advising people to monitor their consumption and for food manufacturers to lower the salt content in their products.
Fruit and vegetables are rich in vitamins and minerals that can lower blood pressure by boosting the body's vessels and arteries.
But the latest study suggests they do not counteract the adverse influence of a salty diet.
It analysed data from the INTERMAP study from 1997 to 1999 where the diets of 4,680 people, aged 40 to 59, from the UK, Japan, China and the US were tracked over over four days.
Two urine samples were taken along with measurements of height, weight and blood pressure.
This allowed the researchers to assess concentrations of sodium, the main component of salt, and potassium which is found in green leafy vegetables and has been linked to lower blood pressure.
Dietary data was also used to assess the volunteers' intake of over 80 nutrients that may be linked to low blood pressure including vitamin C, fibre and omega-3 fatty acids many of which are found in fruit, vegetables and whole grains.
Blood pressure link
The researchers identified a link between high blood pressure and higher salt intake, even in those consuming the most potassium and other nutrients.
The recommended amount of salt in the UK is no more than six grams a day - about a teaspoon. The current average is 8.1g, over two grams more.
The daily average during the study, which was carried out at a time when people were eating even more salt than today - with the UK 8.5g and the US, Japan and China 9.6, 11.7 and 13.4 respectively.
Increasing consumption above these amounts were linked to a increased blood pressure - with an additional seven grams (1.2 teaspoons) of salt associated with a rise in the 'systolic' measurement of 3.7 mmHg.
This is the first of the two numbers that relates to the force with which the heart pumps blood around the body. The second, called 'diastolic', is the resistance to blood flow in the arteries.
Ideally, blood pressure should be between 90/60 and 120/80 mmHg. But just a small reduction can reduce the risk of conditions such as stroke.
Added Dr Chan: "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."
The team acknowledge that because the data was collected over four days, it provides information from a snapshot of time. They now hope to focus on longer term studies, with a greater number of people.
Mhairi Brown, a nutritionist at CASH (Consensus Action on Salt and Health), said: "This robust and extremely well conducted study demonstrates once again the overwhelming importance of reducing our salt intake to stop the devastating effects that high blood pressure has on our health causing strokes and heart disease - the biggest cause of death in the UK.
"By reducing our reliance on processed food we can lower the amount of salt we eat, as well as increasing our intake of healthier nutrients.
"We shouldn't overlook the importance of increasing the amount of potassium we eat, from fruits and vegetables, to protect our general health."
The British Heart Foundation says high blood pressure affects around 16 million people in the UK. An estimated seven million of those are undiagnosed, as there are rarely any symptoms.
It says: "High blood pressure significantly increases the risk of coronary heart disease, stroke and kidney disease."
It advises: "Don't cook with salt or add any to your food at the table, and cut down on processed foods, which contain a lot of salt."
Last year a study of 4,630 men and women aged 25 to 64 who were followed for more than a decade found high salt intake doubled risk of heart failure.