Does cutting down on salt help people with high blood pressure?

By Lilian Anekwe

BMJ Group News

What do we know already?

High amounts of salt in the diet can raise blood pressure. So doctors usually recommend that people avoid salt as much as possible, particularly if they have high blood pressure.

But recently a review of studies suggested that reducing salt alone may not be enough to make a difference to your chances of avoiding a heart attack or stroke.

Worryingly, this review also indicated that, for people with heart failure, cutting down on salt might increase their chances of dying. But this finding came from just one fairly small study, so we need more evidence to be sure that it was not just a chance finding.

This latest review looked at good-quality studies that compared people who had been randomly assigned to follow either a low-salt or high-salt diet. People who had a low-salt diet consumed around 3 grams of salt every day, while those who had a high-salt diet had around 4 grams.

The researchers compared people’s blood pressure, as well as the levels of fats (lipids) in their blood. High blood pressure and high levels of some kinds of lipids, such as LDL cholesterol and triglycerides, can increase people’s risk of a heart attack or stroke.

What does the new study say?

People who followed a reduced-salt diet had lower blood pressure than those who consumed more salt - around 1 percent lower if their blood pressure was normal to begin with and 3.5 percent lower if their blood pressure was high.

However, overall cholesterol was 2.5 percent higher in the low-salt group than in the high-salt group. People following a low-salt diet also had a higher level of bad (LDL) cholesterol, but this difference was not more than we would expect by chance. There was no difference in the amount of good (HDL) cholesterol.

However, people in the low-salt group did have 7 percent higher levels of triglycerides.

How reliable is the research?

The researchers looked at 167 good-quality studies, which looked at more than 65,000 people in total. Combining data from lots of studies in this way gives more reliable results.

But some of the studies included in the review were very short, with many lasting less than four weeks. It may take much longer than this to see what difference reducing salt intake can make. Also, we don’t know how people reduced the amount of salt in their diet. It may be that other changes in their diet affected their blood pressure and lipid levels.

The researchers found that the effects were different in white people, black people, and Asian people, and may be different for men and women. We need more research about the effect of reducing salt in these different people.

What does this mean for me?

These findings suggest that reducing salt might not have an overall beneficial effect on health, given the relatively small reduction in blood pressure and the increase in cholesterol.

But weighing up the effect of reducing salt on people’s health is complicated, and while these findings provide new insight, this isn’t the whole picture.

What we do know is that reducing salt on its own is unlikely to lower your blood pressure much, or prevent heart attacks and strokes. This needs a healthy diet, exercise, and often drugs to treat any existing heart conditions.