Dietary salt reduction- scientists question long-term impact on blood pressure

New research in the UK suggests that reducing the salt intake in people's diets may only have a slight effect on reducing blood pressure in the long term.

The research, carried out by Manchester University in the UK together with the MRC Health Services Research Unit at Bristol University, concludes that alternative ways of reducing salt intake are needed toachieve long-term reductions in blood pressure.

Scientists carried out trials whereby people wereadvised to reduce their salt intake for six months ormore. The results revealed that after one to five years,reducing salt intake resulted in lower blood pressure, butthe effect was small.

Lee Hooper at Manchester University said: "These trials gave very intensive advice on salt reduction, including weekly seminars and workshops, regular feedback on salt reduction achieved and longterm contact via newsletters and meetings.​

Thisintensity 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 weare to achieve long term reductions in blood pressure,"​ he continued.

"Doctors, dietitians and other healthcare workers oftenencourage people to cut down on their salt intake. Thismay be to help reduce raised blood pressure or as partof a preventative healthy eating routine. There is alreadygood evidence that this helps reduce blood pressureshort term. But what is less certain is the long termeffects."​

Professor Shah Ebrahimat the University of Bristol added: "Doctors and nurses areexpected to advise people to reduce their salt intake,but such advice appears to have little effect due to theinherent difficulty people have in changing their diets andsticking with them."​

"This is partly because most salt comes from processedand ready made foods. Efforts by the government toreduce hidden salt in foods such as bread and cerealsmay be more effective as no dietary change isnecessary,"​ he added.

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

According to the research findings people who were on medication to control their bloodpressure are more likely to be able to come off thatmedication (under medical supervision) while keepingtheir blood pressure controlled if they adopt a lower saltdiet.

Professor George Davey Smith at Bristol University said: "Given the public health importance of theissue, and the efforts that are going into reducing salt inprocessed foods, we were surprised by the lack of datalinking efforts to reduce salt to clinical disease.​

Weneed more research in this area and also on the effect ofsalt on later health of infants and children, as theseeffects may be distinct from effects in adults."​

In a statement this week the scientists write that while people in the studies appeared to have reducedtheir salt intake by about a quarter, one year after lowsalt advice was given, they may only have been very careful on the days that salt intake was assessed. This would explain the relatively small effect of thisreduction on blood pressure. According to the results, over the years,measured salt intake increased back towards normal.

The researchers involved in the study are calling for more studies into this area in order to achieve some concrete evidence on the effects on health of low salt dietary advice.

Full findings are published in the 20 September issue of the British Medical Journal​. Leading researcher on the study, Lee Hooper, can be contacted at lee.hooper@man.ac.uk.