April 14, 2014

expert reaction to new study on salt reduction and health

Researchers publishing in BMJ Open report the 15% fall in dietary salt intake over the past decade in England is likely to have had a key role in the 40% drop in deaths from heart disease and stroke over the same period. A before the headlines analysis accompanied these comments.

Professor Rod Taylor, Chair of Health Services Research & Academic Lead, Exeter Clinical Trials Support Network, University of Exeter Medical School, said:

“The study certainly adds to the existing body of observational evidence supporting the health benefit of salt reduction and in particular contributes UK specific data. However, as noted by the authors themselves, observational studies cannot be regarded as a definitive source evidence of the effectiveness of dietary salt reduction, this particular study needing to be interpreted in the context of potential ecological fallacy.” 

Prof David Spiegelhalter, Winton Professor of the Public Understanding of Risk, University of Cambridge, said:

“The authors themselves say that the observed 2.7 mm Hg reduction in systolic BP would be predicted to reduce stroke by approximately 11% and heart attacks by 6%. Even making the large assumption that the whole drop in blood pressure was due to salt reduction, this does not, to me, represent the claimed ‘substantial contribution’ to the observed 40% reduction in deaths from stroke and heart disease.”

Prof Patrick Wolfe, Professor of Statistics, University College London (UCL), said:

“A key issue is that the authors ‘assumed that the changes in BP [blood pressure] from 2003 to 2011, after adjusting for the above variables which included almost all other major factors known to be related to BP, were largely attributable to the changes in population salt intake which occurred during the same period’. However, plausibility of assumption does not equal evidence. On this basis, I do not think that this study has much to add to what we already know. Designed experiments provide much more valuable information than observational studies such as this.”

Victoria Taylor, Senior Dietician at the British Heart Foundation, said:

“There is a wealth of evidence that links a high salt consumption to raised blood pressure, a risk factor for coronary heart disease and stroke. This study is interesting as it looks at what impact salt reduction strategies might have had on stroke and heart disease deaths through reductions in blood pressure. While the reductions in average intakes of salt are a positive change, we mustn’t forget that they are still well above the recommended maximum of 6g a day for adults. As most of the salt we eat is already in our food, it is important that the food industry now works towards meeting the new salt reduction targets to make sure that we can continue to reduce the salt in our diet.”

‘Salt reduction in England from 2003 to 2011: its relationship to blood pressure, stroke and ischaemic heart disease mortality’ by MacGregor et al. published in BMJ Open on Monday 14 April.