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New ways of reducing salt intake needed to make a long-term impact on blood pressure

September 20, 2002

Research has revealed that reducing salt intake in people`s diets only has a slight effect on reducing blood pressure in the long-term.

The research, which was carried out by the University of Manchester and the MRC Health Services Research Unit at the University of Bristol, concludes that alternative ways of reducing salt intake are needed to achieve long-term reductions in blood pressure.

Academics carried out trials where people were advised to reduce their salt intake for six months or more. The results revealed that after one to five years, reducing salt intake resulted in lower blood pressure, but the effect was small.

Lee Hooper from the University of Manchester said: "These trials gave very intensive advice on salt reduction, including weekly seminars and workshops, regular feedback on salt reduction achieved and long-term contact via newsletters and meetings. This intensity of input is not realistic in usual medical practice, but even so the effects on blood pressure were small. We need to find other ways of reducing salt intake if we are to achieve long-term reductions in blood pressure.

"Doctors, dieticians and other healthcare workers often encourage people to cut down on their salt intake. This may be to help reduce raised blood pressure or as part of a preventative healthy eating routine. There is already good evidence that this helps reduce blood pressure short term. But what is less certain is the long-term effects."

Commenting on the research, Shah Ebrahim, Professor of Epidemiology of Ageing at Bristol University, said: "Doctors and nurses are expected to advise people to reduce their salt intake, but such advice appears to have little effect due to the inherent difficulty people have in changing their diets and sticking with them.

"This is partly because most salt comes from processed and ready made foods. Efforts by the government to reduce hidden salt in foods such as bread and cereals may be more effective as no dietary change is necessary.

"At a population level even small reductions in blood pressure can reduce numbers of strokes and heart attacks".

One of the most useful findings of the research was that people who were on medication to control their blood pressure are more likely to be able to come off that medication (under medical supervision) while keeping their blood pressure controlled if they adopt a lower salt diet.

George Davey Smith, Professor of Clinical Epidemiology at Bristol University, said: "Given the public health importance of the issue, and the efforts that are going into reducing salt in processed foods, we were surprised by the lack of data linking efforts to reduce salt to clinical disease. We need more research in this area and also on the effect of salt on later health of infants and children, as these effects may be distinct from effects in adults."

While people in the studies appeared to have reduced their salt intake by about a quarter, one year after low salt advice was given, they may only have been being very careful on the days that salt intake was assessed.

This would explain the relatively small effect of this reduction on blood pressure. Even so, over the years, measured salt intake increased back towards normal.

There is little information from these studies of effects on health as a result of low salt dietary advice. One would expect that reducing blood pressure even a little might reduce strokes and heart disease, but it would be helpful to have some definite evidence of this.

Bristol, University of