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A healthy diet may not offset the effects of a high
salt intake on blood pressure, suggests a new study.
The research, from scientists at a number of
institutions, including Imperial College London and
Northwestern University, analysed the diets of over
4,000 people.
The results, published in the journal Hypertension,
showed that people eating higher amounts of salt had
higher blood pressure, no matter how healthy a
person's overall diet.
The scientists behind the research are now advising
people to monitor their salt intake and for food
manufacturers to 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's thought to have a number of causes, including
age, weight and eating too much salt.
It's thought that vitamins and minerals in fruit and
vegetables might in some way affect blood vessels,
enabling them to lower blood pressure.
Previously, experts believed 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.
In the paper, the team studied data from the
so-called INTERMAP study. In this study, which was
conducted between 1997-1999, scientists tracked the
diets of 4,680 people, aged 40-59, from the USA, UK,
Japan and China.
The volunteers were tracked over four days, and two
urine samples were taken during this time.
Measurements of height, weight and blood pressure
were also taken. The study data has since been used
for numerous research projects.
In the latest paper the team assessed concentrations
of sodium and potassium in the urine samples.
Sodium is the main component of salt, while
potassium, which is found in green leafy vegetables,
has been linked to lower blood pressure.
The team also used dietary data 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 these nutrients are found in fruit,
vegetables and whole grains.
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 was 9.6g, China 13.4g and Japan
11.7g.
Increasing salt intake above this average amount was
linked to an increased 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.
Blood pressure is measured in two numbers - the
first, called systolic pressure, measures the force
the heart pumps blood around the body. The second
number, called diastolic pressure, is the resistance
to blood flow in the arteries.
Ideally, blood pressure should be between 90/60 and
120/80 mmHg. However, reducing blood pressure by
just a small amount can reduce the risk of
conditions such as stroke.
Dr Queenie Chan, joint lead author of the research
from the School of Public Health at Imperial, said
the research shows the importance of cutting salt
intake.
"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."
She added: "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.
For more information
Hypertension
Relation of Dietary Sodium (Salt) to Blood Pressure
and Its Possible Modulation by Other Dietary Factors
Link...
Imperial College London
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School of Public Health
Link...
Northwestern University
Link...
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